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Relationship between Fish Size and Metabolic Rate in the Oxyconforming Inanga Galaxias maculatus Reveals Size-Dependent Strategies to Withstand Hypoxia

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Abstract

Abstract The relationship between metabolic rate and body size in animals is unlikely to be a constant but is instead shaped by a variety of intrinsic (i.e., physiological) and extrinsic (i.e., environmental) factors. This study examined the effect of environmental oxygen tension on oxygen consumption as a function of body mass in the galaxiid fish, inanga (Galaxias maculatus). As an oxyconformer, this fish lacks overt intrinsic regulation of oxygen consumption, eliminating this as a factor affecting the scaling relationship at different oxygen tensions. The relationship between oxygen consumption rate and body size was best described by a power function, with an exponent of 0.82, higher than the theoretical values of 0.66 or 0.75. The value of this exponent was significantly altered by environmental Po2, first increasing as Po2 decreased and then declining at the lowest Po2 tested. These data suggest that the scaling exponent is species specific and regulated by extrinsic factors. Furthermore, the external Po2 at which fish lost equilibrium was related to fish size, an effect explained by the scaling of anaerobic capacity with fish mass. Therefore, although bigger fish were forced to depress aerobic metabolism more rapidly than small fish when exposed to progressive hypoxia, they were better able to enact anaerobic metabolism, potentially extending their survival in hypoxia.

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... Hypoxia tolerance, or the ability of an animal to cope with low environmental oxygen, can be measured as the critical oxygen tension (P crit , sometimes also referred to as limiting oxygen level, LOL), which is defined as the lowest oxygen level at which aerobic metabolism is independent of the ambient partial pressure of oxygen (Grieshaber et al., 1994;Harrison et al., 2018;Hochachka & Somero, 2002;Urbina & Glover, 2013). Under declining oxygen levels and down to P crit , fishes can sustain oxygen uptake rates to fuel their standard metabolic rate (SMR), the minimum rate of oxygen uptake needed to sustain life in a resting, post-absorptive state at a given temperature. ...
... Since the pioneering work of Prosser (Prosser, 1955), there has been debate in the literature about the size-dependency of hypoxia tolerance in fish. Body mass profoundly influences oxygen consumption rates in fishes, both within species (during ontogeny) and across species (Clarke & Johnston, 1999;Killen et al., 2010;Rubalcaba et al., 2020;Urbina & Glover, 2013). Both the capacity for oxygen supply to tissues and metabolic oxygen demand scale with body mass, but if the exact scaling relationship is different, a mismatch in supply and demand occurs such that hypoxia tolerance should vary with size Killen et al., 2016;Rubalcaba et al., 2020;Urbina & Glover, 2013). ...
... Body mass profoundly influences oxygen consumption rates in fishes, both within species (during ontogeny) and across species (Clarke & Johnston, 1999;Killen et al., 2010;Rubalcaba et al., 2020;Urbina & Glover, 2013). Both the capacity for oxygen supply to tissues and metabolic oxygen demand scale with body mass, but if the exact scaling relationship is different, a mismatch in supply and demand occurs such that hypoxia tolerance should vary with size Killen et al., 2016;Rubalcaba et al., 2020;Urbina & Glover, 2013). However, several studies comparing species report no clear effect of mass on P crit in fishes (Nilsson & Östlund-Nilsson, 2008;. ...
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Aerobic metabolism generates 15-20 times more energy (ATP) than anaerobic metabolism , which is crucial in maintaining energy budgets in animals, fueling metabolism, activity, growth and reproduction. For ectothermic water-breathers such as fishes, low dissolved oxygen may limit oxygen uptake and hence aerobic metabolism. Here, we assess, within a phylogenetic context, how abiotic and biotic drivers explain the variation in hypoxia tolerance observed in fishes. To do so, we assembled a database of hypoxia tolerance, measured as critical oxygen tensions (P crit) for 195 fish species. Overall, we found that hypoxia tolerance has a clear phylogenetic signal and is further modulated by temperature, body mass, cell size, salinity and metabolic rate. Marine fishes were more susceptible to hypoxia than freshwater fishes. This pattern is consistent with greater fluctuations in oxygen and temperature in freshwater habitats. Fishes with higher oxygen requirements (e.g. a high metabolic rate relative to body mass) also were more susceptible to hypoxia. We also found evidence that hypoxia and warming can act synergistically, as hypoxia tolerance was generally lower in warmer waters. However, we found significant interactions between temperature and the body and cell size of a fish. Constraints in oxygen uptake related to cellular surface area to volume ratios and effects of viscosity on the thickness of the boundary layers enveloping the gills could explain these thermal dependencies. The lower hypoxia tolerance in warmer waters was particularly pronounced for fishes with larger bodies and larger cell sizes. Previous studies have found a wide diversity in the direction and strength of relationships between P crit and body mass. By including interactions with temperature, our study may help resolve these divergent findings, explaining the size dependency of hypoxia tolerance in fish.
... However, the fishes Fundulus grandis and Galaxias maculatus show a concave downward relationship between b and oxygen level (and L) [121,122]. By lowering L, mild hypoxia may increase the importance of V-related tissue maintenance demand, but more severe hypoxia may not only lower L still further, but also directly affect the ability of the organism to uptake oxygen through body surfaces, thus increasing the importance of SA on metabolic scaling. ...
... The b values for G. maculatus conform nicely to this interpretation (b ~ 1 at mild hypoxia, and b ~ 2/3 at severe hypoxia; see Figure 5), but the b values for F. grandis are quite low at all oxygen levels (0.37 to 0.62 [121]). Oxygen levels may also differentially affect the relative importance of aerobic vs. anaerobic metabolism in small vs. large individuals with relatively high vs. low SA/V ratios, respectively (also see [121,122]). ...
... The metabolic scaling exponent (b ± 95% confidence intervals) of the fish Galaxias maculatus shows a concave downward relationship with oxygen level (data from[122] and M. Urbina, personal communication), as predicted by the metabolic-level boundaries hypothesis (see text). The dotted horizontal lines indicate scaling in relation to volume (b = 1) and surface area (b = 2/3). ...
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Both the slope and elevation of scaling relationships between log metabolic rate and log body size vary taxonomically and in relation to physiological or developmental state, ecological lifestyle and environmental conditions. Here I discuss how the recently proposed metabolic-level boundaries hypothesis (MLBH) provides a useful conceptual framework for explaining and predicting much, but not all of this variation. This hypothesis is based on three major assumptions: (1) various processes related to body volume and surface area exert state-dependent effects on the scaling slope for metabolic rate in relation to body mass, (2) the elevation and slope of metabolic scaling relationships are linked, and (3) both intrinsic (anatomical, biochemical and physiological) and extrinsic (ecological) factors can affect metabolic scaling. According to the MLBH, the diversity of metabolic scaling relationships occurs within physical boundary limits related to body volume and surface area. Within these limits, specific metabolic scaling slopes can be predicted from the metabolic level (or scaling elevation) of a species or group of species. In essence, metabolic scaling itself scales with metabolic level, which is in turn contingent on various intrinsic and extrinsic conditions operating in physiological or evolutionary time. The MLBH represents a “meta-mechanism” or collection of multiple, specific mechanisms that have contingent, state-dependent effects. As such, the MLBH is Darwinian in approach (the theory of natural selection is also meta-mechanistic), in contrast to currently influential metabolic scaling theory that is Newtonian in approach (i.e., based on unitary deterministic laws). Furthermore, the MLBH can be viewed as part of a more general theory that includes other mechanisms that may also affect metabolic scaling.
... Previous respirometry studies on Galaxiidae species have used a closed respirometry procedure [42,43,44,45] based on that of Sloman et al. (2006) [46]. This system allows the use of relatively small respirometers (min = 0.065 L) which has proven the most practical for measuring metabolism in small (often 0.4 g), slowly respiring Galaxiidae species, whose oxygen consumption rates can be otherwise difficult to detect relative to measurement error, in larger respirometers [47,48]. ...
... However, a test of the effect of carbon dioxide accumulation using closed respirometry in another galaxiid fish, showed that elevated carbon dioxide had no impact on oxygen consumption [45]. Consequently, this closed system has provided reliable results over multiple independent studies on Galaxiidae species [42,43,44], including studies done in semi-closed respirometers [49]. To ensure our results were comparable to these studies on Galaxiidae, we used identical closed respirometry methods found therein based on the work of Sloman and colleagues (2006). ...
... Mudfish SMR is 1.7-2.4 times lower than other members of the Galaxiidae family, including Galaxias brevipinnis (0.102 mg O 2 g -1 h -1 ), Galaxias vulgaris (0.117 mg O 2 g -1 h -1 ) and Galaxias maculatus (0.141 mg O 2 g -1 h -1 ) which, like kōkopu, typically inhabit normoxic flowing streams and rivers and struggle to survive hypoxia and drought [42,55,56]. As our study suggests, such an environment is better suited to species with high aerobic scope which could enhance growth, reproductive potential and swimming ability. ...
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Differences in population density between species of varying size are frequently attributed to metabolic rates which are assumed to scale with body size with a slope of 0.75. This assumption is often criticised on the grounds that 0.75 scaling of metabolic rate with body size is not universal and can vary significantly depending on species and life-history. However, few studies have investigated how interspecific variation in metabolic scaling relationships affects population density in different sized species. Here we predict inter-specific differences in metabolism from niche requirements, thereby allowing metabolic predictions of species distribution and abundance at fine spatial scales. Due to the differences in energetic efficiency required along harsh-benign gradients, an extremophile fish (brown mudfish, Neochanna apoda) living in harsh environments had slower metabolism, and thus higher population densities, compared to a fish species (banded kōkopu, Galaxias fasciatus) in physiologically more benign habitats. Interspecific differences in the intercepts for the relationship between body and density disappeared when species mass-specific metabolic rates, rather than body sizes, were used to predict density, implying population energy use was equivalent between mudfish and kōkopu. Nevertheless, despite significant interspecific differences in the slope of the metabolic scaling relationships, mudfish and kōkopu had a common slope for the relationship between body size and population density. These results support underlying logic of energetic equivalence between different size species implicit in metabolic theory. However, the precise slope of metabolic scaling relationships, which is the subject of much debate, may not be a reliable indicator of population density as expected under metabolic theory.
... The specific respiration rates of G. maculatus obtained in this study ranged from 0.0017-0.0087 g O 2 g −1 d −1 and were in agreement with values produced over more limited ranges of temperatures or body masses (Encina-Montoya et al. 2011;Milano et al. 2013;Urbina & Glover 2013). In previous studies, the respiration rate for G. maculatus had been estimated for fixed temperatures and varying masses. ...
... Ríos (1979) determined the allometric relationship between oxygen consumption and body size (on the order on 0.1-2 g) at 15°C for lake and river populations of G. maculatus as R (mL O 2 h −1 ) = 0.25 W 0.61 (lake) and R = 0.269 W 0.60 (river), finding no significant differences between the slopes for both populations. More recently, Encina-Montoya et al. (2011) reported b = 0.612 for G. maculatus at 12°C (0.02-1.5 g), whereas Urbina & Glover (2013) reported b = 0.82 at 14°C (0.14-11.28 g). Our estimate of RB was −0.31 when fit simultaneously to body mass and temperature. ...
... After converting RB in this study from a specific rate (g O 2 g −1 d −1 ) to an absolute rate by adding 1.0, a value of 0.69 (g O 2 d −1 ) was produced in units comparable to the other studies. The allometric slope from our study, while accounting for a broad range of temperatures and an ecologically relevant range of body masses, was similar to two of the three studies (Ríos 1979;Encina-Montoya et al. 2011) conducted at single temperatures, but deviated more from the study that included a much broader range of body masses, including extremely large individuals (Urbina & Glover 2013). While this potential shift in the allometry of respiration associated with larger sizes deserves further attention, most G. maculatus landlocked populations are predominantly composed of sizes approximately 80 mm (2-3 g) or smaller. ...
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Body mass and temperature are primary determinants of metabolic rate in ectothermic animals. Oxygen consumption of post-larval Galaxias maculatus was measured in respirometry trials under different temperatures (5–21 °C) and varying body masses (0.1– >1.5 g) spanning a relevant range of thermal conditions and sizes. Specific respiration rates (R in g O 2 g −1 d −1) declined as a power function of body mass and increased exponentially with temperature and was expressed as: R = 0.0007 * W −0.31 * e 0.13 * T. The ability of this model to predict specific respiration rate was evaluated by comparing observed values with those predicted by the model. Our findings suggest that the respiration rate of G. maculatus is the result of multiple interactive processes (intrinsic and extrinsic factors) that modulate each other in 'meta-mechanistic' ways; this would help to explain the species' ability to undergo the complex ontogenetic habitat shifts observed in the lakes of the Andean Patagonic range. ARTICLE HISTORY
... O 2 consumption was measured in fish via closed box respirometry (Urbina et al., 2012;Urbina and Glover, 2013). At cessation of the Zn exposure, fish were placed individually into 0.25 L Schott glass bottles and covered with plastic mesh so water could flow in. ...
... Random assortment of fish into treatment groups resulted in a significant size difference between groups. To account for this the scaling relationship between size and metabolic rate in inanga (from Urbina and Glover, 2013) was used to normalise all O 2 consumption values to a 1 g fish. Following respirometry, fish were euthanised with an anaesthetic overdose (1 g L −1 3-aminobenzoic acid ethylester; MS-222) followed by severing of the spinal cord. ...
... whether environmental variables modify the mass exponent). Studies on this topic have shown that temperature (Glazier 2005;Killen et al. 2010;Verberk and Atkinson 2013;Carey and Sigwart 2014) and oxygen tension (Urbina and Glover 2013) influence the mass exponent. Our study is one of the first that explores the effects of oxygen tension on the mass scaling of a crustacean species. ...
... In our study, we clearly demonstrate that oxygen tension alters the metabolic scaling in P. laevigatus; scaling exponents increase with increasing oxygen tension up to 9-14 kPa before declining again. Interestingly, Urbina and Glover (2013) showed that scaling exponents peaked at intermediate oxygen tensions in inanga Galaxias maculatus in a similar way. Although our limited data set does not allow for detailed inferences about the mechanistic basis of the observed response, it does show that physiological responses to low oxygen exposure co-vary with size and life-stage. ...
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For aquatic breathers, hypoxia and warming can act synergistically causing a mismatch between oxygen supply (reduced by hypoxia) and oxygen demand (increased by warming). The vulnerability of these species to such interactive effects may differ during ontogeny due to differing gas exchange systems. This study examines respiratory responses to temperature and hypoxia across four life-stages of the intertidal porcelain crab Petrolisthes laevigatus. Eggs, megalopae, juveniles and adults were exposed to combinations of temperatures from 6 to 18 °C and oxygen tensions from 2 to 21 kPa. Metabolic rates differed strongly across life-stages which could be partly attributed to differences in body mass. However, eggs exhibited significantly lower metabolic rates than predicted for their body mass. For the other three stages, metabolic rates scaled with a mass exponent of 0.89. Mass scaling exponents were similar across all temperatures, but were significantly influenced by oxygen tension (the highest at 9 and 14 kPa, and the lowest at 2 kPa). Respiratory responses across gradients of oxygen tension were used to calculate the response to hypoxia, whereby eggs, megalopae and juveniles responded as oxyconformers and adults as oxyregulators. The thermal sensitivity of the metabolic rates (Q10) were dependent on the oxygen tension in megalopae, and also on the interaction between oxygen tension and temperature intervals in adults. Our results thus provide evidence on how the oxygen tension can modulate the mass dependence of metabolic rates and demonstrate changes in respiratory control from eggs to adults. In light of our results indicating that adults show a good capacity for maintaining metabolism independent of oxygen tension, our study highlights the importance of assessing responses to multiple stressors across different life-stages to determine how vulnerability to warming and hypoxia changes during development.
... Furthermore, Nilsson and Östlund-Nilsson (2008) showed that P crit did not correlate with body mass in juvenile and adult damselfish (Pomacentridae) ranging between 10 mg and 40 g but that smaller fish were much less tolerant to hypoxia below P crit , owing to their limited capacity for meeting ATP demand through anaerobic metabolism. These findings were further supported in G. maculatus (Urbina and Glover, 2013). These results illustrate the benefit of considering P crit alongside other methods of determining hypoxia tolerance, such as measurements of tissue-specific lactate accumulation and determinations of the loss of equilibrium of 50% of the fish, in order to assess overall hypoxia tolerance (Urbina and Glover, 2013;Speers-Roesch et al., 2013;Claireaux and Chabot, 2016). ...
... These findings were further supported in G. maculatus (Urbina and Glover, 2013). These results illustrate the benefit of considering P crit alongside other methods of determining hypoxia tolerance, such as measurements of tissue-specific lactate accumulation and determinations of the loss of equilibrium of 50% of the fish, in order to assess overall hypoxia tolerance (Urbina and Glover, 2013;Speers-Roesch et al., 2013;Claireaux and Chabot, 2016). ...
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Hypoxia is a common occurrence in aquatic habitats, and it is becoming an increasingly frequent and widespread environmental perturbation, primarily as the result of anthropogenic nutrient enrichment and climate change. An in-depth understanding of the hypoxia tolerance of fishes, and how this varies among individuals and species, is required to make accurate predictions of future ecological impacts and to provide better information for conservation and fisheries management. The critical oxygen level (Pcrit) has been widely used as a quantifiable trait of hypoxia tolerance. It is defined as the oxygen level below which the animal can no longer maintain a stable rate of oxygen uptake (oxyregulate) and uptake becomes dependent on ambient oxygen availability (the animal transitions to oxyconforming). A comprehensive database of Pcrit values, comprising 331 measurements from 96 published studies, covering 151 fish species from 58 families, provides the most extensive and up-to-date analysis of hypoxia tolerance in teleosts. Methodologies for determining Pcrit are critically examined to evaluate its usefulness as an indicator of hypoxia tolerance in fishes. Various abiotic and biotic factors that interact with hypoxia are analysed for their effect on Pcrit, including temperature, CO2, acidification, toxic metals and feeding. Salinity, temperature, body mass and routine metabolic rate were strongly correlated with Pcrit; 20% of variation in the Pcrit data set was explained by these four variables. An important methodological issue not previously considered is the inconsistent increase in partial pressure of CO2 within a closed respirometer during the measurement of Pcrit. Modelling suggests that the final partial pressure of CO2 reached can vary from 650 to 3500 µatm depending on the ambient pH and salinity, with potentially major effects on blood acid–base balance and Pcrit itself. This database will form part of a widely accessible repository of physiological trait data that will serve as a resource to facilitate future studies of fish ecology, conservation and management.
... This is particularly important in aquatic animals since they have to cope with changes in dissolved oxygen concentrations throughout the different stages of their life cycle as they move between different bodies of water. Such fluctuations in oxygen availability will at some point affect the capacity of organisms to uptake and utilize oxygen (Urbina and Glover 2013). Most aquatic animals are oxyregulators, meaning that they can maintain oxygen consumption (MO 2 ) constant down to a certain oxygen level, which varied depending on the organism (Prosser and Brown 1973). ...
... This likely shows P. pugnax is equally adapted to hypoxia during its whole ontogeny, as a result of the prevalent and stable hypoxic conditions within its burrows. Whole animal anaerobic capacity, however, is expected to scale with body mass, as a bigger animal holds more tissue able to anaerobically metabolize (Sloman et al. 2006;Urbina and Glover 2013). There are cases where the relationship between body mass and anaerobic metabolism behaves similarly to aerobic metabolism, such as that of E. mucronata, which shows an increase in the specific activity of LDH per unit of mass throughout its development (González and Quiñones 2002). ...
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Metabolic scaling is a well-known biological pattern. Theoretical scaling exponents near 0.67 and 0.75 are the most widely accepted for aerobic metabolism, but little is known about the scaling of anaerobic metabolism. Furthermore, metabolic scaling has been mainly evaluated in organisms primarily relying on aerobic pathways. Here we evaluate both aerobic and anaerobic metabolic scaling in Parastacus pugnax, a burrowing freshwater crayfish endemic to Chile, which inhabits waters with low pO2 (~ 1 mg O2 L⁻¹, measured in this study). We determined the metabolic rate, total oxidative capacity (Electron Transport System: ETS), critical oxygen tension (Pcrit) and muscular Lactate dehydrogenase (LHD) and Malate dehydrogenase (MDH) enzymatic activities (proxies of anaerobic metabolism) over a wide range of P. pugnax sizes (0.24–42.93 g wet mass). Aerobic metabolism scaled with crayfish size with an exponent of 0.78, remarkably similar to the 0.73 which scaled the ETS, the enzymatic complex behind respiration. Critical partial pressure of oxygen (Pcrit) was calculated as 15.6 ± 2.9 mmHg, showing that aerobic metabolism was efficiently maintained until ~ 10% air saturation. Below this threshold, P. pugnax switched to anaerobic metabolism, evidenced by a reduction in aerobic metabolism and ETS activity under chronic low oxygen conditions. None of the activities of MDH, LDH, their ratio (MDH/LDH), nor Pcrit scaled with crayfish size, indicating that these animals are equally adapted to hypoxic environments throughout their whole ontogeny. Given the particularities of its habitat, the information presented here is valuable for a proper management and successful conservation.
... Establishing optimum sampling times to control circadian rhythm influences on the metabolome is also suggested.224 Among the intrinsic variables, body size, activity state, sex and age all influence the metabolome.[225][226][227] Therefore, unless they are the area of interest, they should be controlled for via sample group matching or through modelling of confounding variables during downstream statistical analyses. ...
... Therefore, unless they are the area of interest, they should be controlled for via sample group matching or through modelling of confounding variables during downstream statistical analyses. Activity state is difficult to control at an individual level, but should be a consideration to reduce metabolic biases among samples.[225][226][227] Concerning non-invasive sampling, standard protocols have been established to allow cross-study comparisons. ...
Article
Salmonids are the third major farmed finfish species after carps and tilapines, and thus contribute to global food fish production. However, as the aquaculture industry continues to grow, several challenges have emerged. Left unchecked, current problems will hinder aquaculture development. Metabolomics is one of the powerful biotechnological tools that will contribute to solving some of the pressing problems. This review aims to summarise findings and identify gaps from studies that used metabolomics in farmed salmon research. We extracted methodological information for comparison, highlighted analytical platform usages and identified most studied salmonids and sample types. We reviewed key articles to highlight the latest research themes. From the identified research gaps, future perspectives regarding potential use of metabolomics to solve issues in ecotoxicology, thermotolerance, nutrition, post‐harvest quality, health and disease, and husbandry practices are provided. The survey also highlighted improvements in execution of metabolomics protocols in aquaculture.
... Under chronic hypoxia, teleost fish reduce aerobic scope for activity by decreasing the maximum metabolic rate (MO 2 max, maximum rate of oxygen consumption), whereas standard metabolic rate (SMR; minimal rate of oxygen consumption) is maintained for facilitation of essential functions (Domenici et al., 2017). However, there are species-specific differences in these relationships, which also change with fish size and age (Urbina and Glover, 2013) and are indicative of tolerance/sensibility to hypoxia conditions. ...
... Glucose energy stores released into plasma in exercised normoxic fish may have been depleted in hypoxic fish prior to exercise, as indicated by elevated plasma lactate in resting Cojinoba subjected to hypoxia. Circulating red blood cell concentration, which can be increased through splenic contraction as a rapid response to immediate need for oxygen (Richards, 2009;Speers-Roesch et al., 2013;Urbina and Glover, 2013), may have been affected by lysis in extreme stress (Burgos-Aceves et al., 2019;Wedemeyer and Yasutake, 1977) in the present study, as indicated by observations of red plasma in fish exercised to fatigue in hypoxia. It is possible that high lactate concentration led to hemolysis via osmolarity imbalance (Black, 1958;Speers-Roesch et al., 2013). ...
Article
Understanding environmental constraints and associated physiological adaptations of culture organisms is key for the implementation of off-shore grow-out facilities. In the southeast Pacific Ocean along the coasts of Chile and Peru, seasonal upwelling events lead to hypoxic conditions, which are projected to increase in both frequency and intensity with climate change. Aquaculture operations must take into account the physiological adaptability of a species for environmental conditions. For Cojinoba (Seriolella violacea, Guichenot, 1848), a native target species for aquaculture diversification in northern Chile, little is known in regard to physiological capacity for hypoxia. Therefore, hypoxia tolerance studies were conducted followed by measurement of resting and active metabolism and associated energy facilitation in response to hypoxia in juvenile Cojinoba. Hypoxia tolerance studies found they were resilient to dissolved oxygen levels of 1.0 mg O2 Lˉ¹ for 8 h. Swimming metabolism studies exposed Cojinoba to normoxia (7.5 mg O2 Lˉ¹) or hypoxia (1.0 mg O2 Lˉ¹), and quantified minimum metabolic rate (MO2 min), active metabolic rate (MO₂ max), critical swimming speed (Ucrit) and associated energetic metabolites and hematological variables. In hypoxia, there was a decrease in MO₂ max (34%) leading to a large (82%) decrease in aerobic metabolic scope. MO2 min decreased as well by 12%, with lactate increasing presumably to temporarily maintain basic metabolic function. In addition, Ucrit decreased by 53% in hypoxia, although tail beat frequency was similar in normoxia and hypoxia up to a velocity of 40 cm s⁻¹. Moreover, although erythrocyte concentration increased in hypoxia, hemolysis was observed in exercised fish in this condition. There was a notable increase (5-fold compared to normoxia) in lactate levels of exercised fish in the hypoxia group, which suggests a quick conversion to anaerobic metabolic pathways to maintain energy balance when swimming in hypoxic environments. Therefore, Cojinoba have adaptive responses that may facilitate survival during severe hypoxic events although overall physiological performance is diminished.
... The scaling coefficients and the scaling exponents for all of these relationships are listed in Table 3. Slopes from the regressions were not statistically different between bester and beluga, but were statistically higher in the case of sterlet sturgeon. Additionally, it can be observed that large fish consume more oxygen, which is reflected in higher metabolic rates than small fish, but on a unit weight basis, small fish will consume more oxygen than larger fish [41]. Table 3. Relationship between oxygen uptake and mass of sturgeon species. ...
... The results of the present study, and other similar studies (Table 4), emphasize the lessening of metabolism with the increase of body weight. However, the metabolic rate variation does not depend only on weight but rather on of a series of intrinsic and extrinsic factors [41]. For example, some authors consider that a lower metabolic rate of some sturgeon species could partially be assigned to their depressed swimming ability [45]. ...
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In the present study, oxygen consumption of two sturgeon species, beluga (Huso huso), sterlet (Acipenser ruthenus), and their hybrid reared in a recirculating aquaculture system were compared over body intervals from 54–107 g to determine the interspecific variation of metabolic rate. Metabolic rates were measured using the intermittent-flow respirometry technique. Standard oxygen consumption rates (SMR, mg O2 h−1) of sterlet were 30% higher compared with beluga and 22% higher compared with bester hybrid. The routine metabolic rate (RMR, mg O2 h−1) averaged 1.58 ± 0.13 times the SMR for A. ruthenus, 1.59 ± 0.3 for H. huso, and 1.42 ± 0.15 for the hybrid bester. However, the study revealed no significant differences (p > 0.05) between mean values of SMR and RMR for beluga and bester hybrid. The scaling coefficient reflected a closed isometry for the hybrid (b = 0.97), while for the purebred species the coefficient of 0.8 suggests a reduction in oxygen consumption with increasing body mass. These findings may contribute to understanding the differences in growth performances and oxygen requirements of the studied species reared in intensive aquaculture system.
... The results of the fourth week (Figure 3), along with the downward trend in the DO 2 consumption observed throughout the study, suggest that a better adaptation to acidic conditions is achieved when fish has a greater body weight. The relationship between the metabolic rate and the body size of fish varies according to intrinsic and extrinsic factors, such as the animal physiology and environmental conditions, respectively (Urbina & Glover, 2013). . Consumption of dissolved oxygen by juvenile tilapia after four hours inside respirometers. ...
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The present work aimed at determining the tolerance of Nile tilapia juveniles to highly acidic rearing waters and the effects of water acidity on the quality of tank effluents. The experimental design consisted of four treatments with different water pH values (4.12 ± 0.84; 5.13 ± 0.74; 6.14 ± 0.64 and 8.06 ± 0.48), with five replicates each. No exchange of water was performed throughout the study, only water replenishment to maintain the initial level. Variables of water quality, soil, growth performance, metabolism and effluents were monitored for eight weeks. Despite the lower total ammonia nitrogen (TAN) concentration in the pH 8 tanks, their levels of non-ionized ammonia (NH3) were the highest ones. At the end, the lowest body weight of fish was observed in the pH 8 tanks. There was a significant improvement in feed conversion ratio (FCR) and protein efficiency ratio (PER) due to to water acidification. There were reduced concentrations of NH3 in the acidified tanks’ effluents. It was concluded that the gradual water acidification up to pH 4 can improve the Nile tilapia juveniles’ growth performance. © 2015, Eduem - Editora da Universidade Estadual de Maringa. All rights reserved.
... For instance, in the study by which suggested G. maculatus to be an oxygen conformer, they also found their experimental fish to show a lactate build-up, indicative of anaerobiosis occurring in progressive hypoxia, as well as showing regulatory responses as increased levels of haemoglobin and increased ventilation (Urbina et al., 2011). Lastly, if SMR is not established in normoxia Urbina & Glover, 2013), defining whether a fish is an oxygen regulator or conformer is rationally challenging. It is well known that to establish an accurate estimate of SMR a fish needs to be resting in the respirometer for a considerable time prior to data collection Keys, 1930b;Snyder et al., 2016;Steffensen, 2002). ...
Article
This study investigated the oxygen consumption of the putative oxygen conformer marbled swamp eel Synbranchus marmoratus during progressive hypoxia. Earlier studies have not reached agreement on whether S. marmoratus is a conformer or regulator. Our results support the view that S. marmoratus is an oxygen regulator, like most bony fishes. This article is protected by copyright. All rights reserved.
... However, since the exposed zone had higher speed currents (1.29 ± 0.35 m s −1 ) and oxygen availability (7.2 ± 1.5 mg O 2 L −1 ) than the sediments of the protected zone (0.37 ± 0.02 m s −1 , 4.5 ± 1.0 mg O 2 L −1 ), the exposed zone might be better able to recycle the nutrients inputs from the salmon farming activities. Oxygen undoubtedly is crucial to aquatic life (Hochachka, 1980;Urbina and Glover, 2013) and its availability is likely to cause differences not only in the degradation rates of organic matter, but also in the macro faunal composition. In fact changes at community structure and escape behavioral responses to hypoxia have been commonly documented in fish (Urbina et al., 2011), but also in marine benthic invertebrates (Riedel et al., 2008). ...
Article
The impacts of any activity on marine ecosystems will depend on the characteristics of the receptor medium and its resilience to external pressures. Salmon farming industry develops along a constant gradient of hydrodynamic conditions in the south of Chile. However, the influence of the hydrodynamic characteristics (weak or strong) on the impacts of intensive salmon farming is still poorly understood. This one year study evaluates the impacts of salmon farming on the marine sediments of both protected and exposed marine zones differing in their hydrodynamic characteristics. Six physico-chemical, five biological variables and seven indexes of marine sediments status were evaluated under the salmon farming cages and control sites. Our results identified a few key variables and indexes necessary to accurately evaluate the salmon farming impacts on both protected and exposed zones. Interestingly, the ranking of importance of the variables and the temporality of the observed changes, varied depending on the hydrodynamic characteristics. Biological variables (nematodes abundance) and environmental indexes (Simpson's dominance, Shannon's diversity and Pielou evenness) are the first to reflect detrimental impacts under the salmon farming cages. Then the physico-chemical variables such as redox, sulphurs and phosphorus in both zones also show detrimental impacts. Based on the present results we propose that the hydrodynamic regime is an important driver of the magnitude and temporality of the effects of salmon farming on marine sediments. The variables and indexes that best reflect the effects of salmon farming, in both protected and exposed zones, are also described.
... Oxygen consumption was determined by closed respirometry, a technique already employed by Urbina and Glover (2013) in G. maculatus. Fish (n = 12 for 'Summer' conditions and n = 11 for 'Winter' conditions) were transferred to individual chambers (517.4 ml each, a volume large enough to allow spontaneous fish movements), made of translucent plastic material. ...
Article
The puyen Galaxias maculatus is a fast-growing species, and the studied population at the southernmost extreme of the species' distribution (54°S) has the shortest growing season among the South American populations (least daylight hours and lowest temperatures), as well as the largest size. Thus, it offers an opportunity to study the effects of strong seasonal variation. The energy allocation pattern on a diadromous population of the species and the influence of ‘Winter’ (4 °C, light:dark photoperiod of 7:17) and ‘Summer’ (10 °C, light:dark photoperiod of 17:7) experimental conditions on the bioenergetics of the species were studied using both physiological and biochemical indicators. Somatic growth, energy density, food consumption, oxidative metabolism and oxygen consumption were measured.
... According to this, O. nigricans showed a decrease in its K and ED with higher AT, promoting then the selection of lower PTs in relation to the experienced AT. On the contrary, diadromous G. maculatus in freshwater decreased its K and ED with decreasing AT. Urbina & Glover (2013) and Boy et al. (2017) suggested that this species has the capability to sustain the metabolic rate under a broad range of external conditions at the expense of obtaining energy from somatic reserves. However, the lowest AT appeared to be the least favourable to support the energetic demands, explaining the selection of higher PT at 2°C. ...
Article
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The aim of this work was to analyze the thermal responses of Odontesthes nigricans, Eleginops maclovinus and diadromous Galaxias maculatus, key species in estuarine areas of the Beagle Channel (Tierra del Fuego, Argentina), under a climate change scenario. We hypothesized that in the southernmost limit of the species’ distribution, individuals are more likely to be affected by indirect consequences of climate change rather than direct temperature mortality. Their thermal tolerance limits were assessed using the Critical Thermal Methodology and their preferred temperatures, using a thermal gradient. Additionally, the Fulton’s condition factor and the energy density of individuals were analyzed as a proxy of the condition of fishes acclimated to different temperatures. Results showed that species analyzed have the ability to acclimate to the different temperatures, intermediate to large tolerance polygons and positive relationships between preferred and acclimation temperatures, indicating their eurythermic nature. Thus, O. nigricans, E. maclovinus and diadromous G. maculatus populations from Tierra del Fuego could experience enhanced performances because of moderate warming being and, as it was hypothesized, be influenced by indirect consequences of climate change (habitat degradation or changes in trophic structure) since they are living in environments that are widely cooler than their maximum tolerance.
... Hypoxia tolerance has been generally shown to be a size-independent trait in fish (Nilsson and Östlund-Nilsson 2008), although there are exceptions (Pan et al. 2016). There is, however, some evidence of species-specific allometric relationships of several traits (e.g., acceleration, metabolic capacity, and metabolic enzyme activity) that may significantly influence sprint performance (Goolish 1991;Norton et al. 2000;Everett and Crawford 2010;Vandamm et al. 2012;Urbina and Glover 2013;Gerry et al. 2016). Overall, because of the small size range of our fish, relatively short time intervals between tests, and a lack of statistical indication of any effects, we concluded that influences of individual size and growth do not merit further discussion. ...
Article
Annual hypoxia in the Chesapeake Bay has expanded to the point where Darwinian fitness of juvenile striped bass (Morone saxatilis) may depend on their ability to perform in low-oxygen environments. The locomotion they use in predator/prey dynamics relies primarily on white (type II) muscle that is powered by anaerobic metabolic pathways and has generally been thought to be immune to aquatic hypoxia. We tested the sprint performance of 15 juvenile striped bass twice under acute hypoxia (20% air saturation [AS]) 5 wk apart and once under normoxia (>85% AS) in between. Average sprint performance was lower under the first hypoxia exposure than in normoxia and increased in the second hypoxia test relative to the first. The rank order of individual sprint performance was significantly repeatable when comparing the two hypoxia tests but not when compared with sprint performance measured under normoxic conditions. The maximum sprint performance of each individual was also significantly repeatable within a given day. Thus, sprint performance of striped bass is reduced under hypoxia, is phenotypically plastic, and improves with repetitive hypoxia exposures but is unrelated to relative sprint performance under normoxia. Since energy to fuel a sprint comes from existing ATP and creatine phosphate stores, the decline in sprint performance probably reflects reduced function of a part of the reflex chain leading from detection of aversive stimuli to activation of the muscle used to power the escape response.
... This is consistent with the significantly positive effect of DO on the occurrence of juvenile fishes, though there was no significant effect on adult occurrence. Evidence generally suggests that bigger fishes are better equipped than smaller fishes to tolerate periods of suboptimal oxygen conditions (Urbina and Glover 2013). This is attributed to larger stores of glycogen available for anaerobic metabolism, and greater reservoirs for the accumulation of toxic anaerobic end products (Almeida-Val et al. 2000, Nilsson and Östlund-Nilsson 2004, Everett and Crawford 2009). ...
... The average weight of groups B and C were 0.35 ± 0.00 g, hence, the number of fish in each aquarium has the largest quantity (A=344 fish, B=239 fish, and C=116 fish). Urbina and Glover (2013) stated that smaller fish require more oxygen, compared to larger fish. The survival of fish is also influenced by fluctuated temperature. ...
Article
The growth rate highly varies in nurseries of eel. Variations in size lead to competition in obtaining feed, this causes stunting of smaller fish. This situation leads to high production costs due to poor feed utilization efficiency. Grading needs to be done periodically to improve nursery production performance. Water quality is controlled by a recirculation system that can support production performance through the degradation of toxic compounds. This study aims to analyze the production and nursery performance of graded eel (Anguilla bicolor bicolor) that graded in the same batch in a recirculation system. Completely randomized design (CRD) consisting of three treatments with four replications was used in this research. The treatments included nursery of graded eels for 60 days in three groups of initial weight size, namely 0,35±0,00 g (A); 0,50±0,00 g (B); and 1,04±0,00 g (C). There were 344 eels (A), 239 eels (B), and 116 eels (C) in each replication. The best nursery production performance was obtained in the treatment of 1,04±0,00 g, and the best nursery business performance was obtained in the treatment of 0,50±0,00 g.
... burrowsius in water was low (2·4 ± 0·4 μmol O 2 g −1 h −1 ) compared with previous reports in other galaxiids such as G. nigrostriata (c. 21 μmol O 2 g −1 h −1 ; Thompson & Withers, 1999) and G. maculatus (semi-closed respirometry 9·3 ± 2·1 μmol O 2 g −1 h −1 , ; closed respirometry c. 9·32 μmol O 2 g −1 h −1 , Urbina & Glover, 2013), but are in agreement with a previous report for this species (c. 1·73 μmol O 2 g −1 h −1 ; Meredith et al., 1982). ...
Article
The Canterbury mudfish Neochanna burrowsius was found to be a pseudo-aestivating galaxiid with a low metabolic rate and significant cutaneous oxygen uptake (c. 43%) in both air and water. Another galaxiid, inanga Galaxias maculatus, had a higher metabolic rate in both media but the proportion of oxygen uptake met by cutaneous respiration rose significantly from 38 to 63% when the fish were exposed to air. Besides its important role in oxygen uptake, the skin of both species also contributed significantly to excretion of carbon dioxide in air, indicating the critical role of the integument as a respiratory tissue. In air, G. maculatus may increase cutaneous gas exchange to meet metabolic demands owing to the reduced utility of the gills, but as emersed G. maculatus were only able to maintain metabolic rates at c. 67% of that measured in water, this strategy probably only permits short-term survival. By contrast, the low and unchanging metabolic rate in water and air in N. burrowsius is a feature that may facilitate tolerance of long periods of emersion in the desiccating environments they inhabit.
... physiology) and extrinsic factors (i.e. environmental parameter) (Urbina & Glover, 2013). Scabra et al. (2016) reported that the oxygen consumption level of elver with size of 10 g/ind was 0.36 mg O2/g/ hour. ...
Article
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p align="center"> ABSTRACT This study aimed to analyze the effect of water temperature on the physiological condition and growth performance of freshwater eel elver Anguilla bicolor bicolor (McClelland, 1844). This study was conducted in March 2017 at the Physiology Laboratory of Aquatic Animal, Faculty of Fisheries and Marine Sciences, Bogor Agricultural University. The study used a completely randomized design with five different levels of temperature (22<sup>°</sup>C, 24<sup>°</sup>C, 26<sup>°</sup>C, 28<sup>°</sup>C, and 30<sup>°</sup>C) as treatments with two replications. The size of elver was 2‒3 g. Fish were fed with 1 mm pellet containing 45% of protein. The feeding level was 7 % of fish biomass and the feeding frequency was two times a day. The results showed that temperatures range from 24‒30<sup>°</sup>C could be used for freshwater eel elver rearing and 28‒30<sup>°</sup>Cwere the best temperatures to support survival and growth performance of eel elver. A temperature of 24<sup>°</sup>C was the best temperature that could reduce the metabolism rate and did not cause stress on the elver. Keywords: elver, physiological conditions, growth performance, metabolism, temperature ABSTRAK Penelitian dengan tujuan menganalisis pengaruh suhu terhadap kondisi fisiologis dan kinerja pertumbuhan elver ikan sidat ( Anguilla bicolor bicolor McClelland, 1844) telah dilakukan pada bulan Maret 2017 di Laboratorium Fisiologi Hewan Air FPIK IPB. Penelitian menggunakan rancangan acak lengkap dengan lima perlakuan suhu berbeda (22<sup>°</sup>C, 24<sup>°</sup>C, 26<sup>°</sup>C, 28<sup>°</sup>C, dan 30<sup>°</sup>C) dengan masing-masing dua ulangan. Ukuran benih yang digunakan 2‒3 g. Pakan yang diberikan berupa pellet berukuran 1 mm dengan kadar protein 45%. Jumlah pakan yang diberikan (FR) adalah 7% dari biomassa ikan dan diberikan dua kali sehari. Hasil penelitian menunjukkan bahwa kisaran suhu 24‒30<sup>°</sup>C dapat digunakan dalam pemeliharaan elver ikan sidat, dan suhu 28‒30<sup>°</sup>C merupakan suhu yang sangat baik untuk mendukung kelangsungan hidup dan pertumbuhan elver ikan sidat. Suhu media 24<sup>°</sup>C adalah suhu terbaik yang dapat menekan laju metabolisme dengan tidak menyebabkan stres pada elver ikan sidat. Kata kunci: elver , kondisi fisiologis, kinerja pertumbuhan, metabolisme, suhu </p
... Oxygen is the fuel that drives metabolism. According to a study by Urbina and Glover, (2012), fish under hypoxic conditions will attempt to maintain oxygen consumption however at a point, this measure will decline with the fall in the partial pressure of oxygen. The study shows that the cost of increasing gill ventilation under the low oxygen saturation threshold eventually becomes exhaustive and counteractive, and fish resort to oxyconformation by reducing oxygen demand and uptake. ...
Research
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In order to get access to limited resources in the environment, the Oreochromis niloticus has been observed to resort to agonistic interactions, the winner of such interaction generally being a high-ranking individual in the observed group. This study investigated the effects of dominance hierarchies on behavior and physiological responses within three groups of Nile tilapia in an experimental setup consisting of clear glass aquaria. Several trials were run to observe how scale loss, gill ventilation rates and aggression with reducing oxygen levels, as well as food deprivation 72 hours were influenced by hierarchy expression in the different social groupings and how that affected observed growth and biological indices and hematological evaluations of dominant and subordinate fish. The results of this study provide evidence to the fact that out of the practice of graded culture must therefore be adopted in order to reduce the effects of hierarchies in aquaculture production of Nile tilapia.
... Additionally, fish size and its growth rate are intrinsically linked to its metabolic rate. Slow metabolism species usually reach larger sizes as they do it a slower growth rate, while high metabolic species grow faster, but will be limited to smaller sizes due to the inherent limitations linked to higher metabolic activities (Clarke and Johnston 1999;Urbina and Glover 2013;Rosenfeld et al. 2015). In conclusion the two identified groups of batoids are very likely to be impacted in different ways by fishing (i.e. ...
Article
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Life-history traits provide a way to estimate the vulnerability of both individuals and populations of a species to disturbance (e.g., overexploitation, climate change). Life-history traits compilations for species of batoids in the Northeast Atlantic (NEA) and the Mediterranean Sea (MED) are scarce, outdated, and generally limited to a local or a regional scale. A literature review compiling values of 10 life-history traits describing the growth, reproductive and feeding strategies of 14 batoids in the NEA and the MED was performed. Via a principal components analysis (PCA) the main drivers of variance and (groups of) similar species were identified. Significant data gaps were revealed for natural mortality and lifespan, for most of the life-history traits of small-eyed ( Raja microocellata ), shagreen ( Leucoraja fullonica ), and sandy ( Leucoraja circularis ) ray, and specifically for the English Channel and Bay of Biscay. The common skate complex ( Dipturus batis complex ) and white ( Rostroraja alba ) skate were found to be different from the rest of the species due to their larger sizes, relatively slow growth, and late maturity, which may make them more vulnerable to overexploitation, while the Raja spp. and Leucoraja spp. rays tend to be smaller species growing at faster rates. Growth and reproductive life-history should be considered as vulnerability to disturbance proxies, be used to update/establish management measures (i.e. minimum size) and enhance the stock assessment predictive ability (i.e. length based-indicators). Future research should be directed towards filling important regional data gaps and providing robust estimation for unreported parameters, such as natural mortality.
... Several fish species are known to survive under very low DO concentrations because under progressive hypoxia, the adult fish are forced to depress aerobic and enacted anaerobic www.nature.com/scientificreports/ metabolism to extend their survival 37 . Nonetheless, larger body-size adults tend to have higher oxygen demand, and therefore, when expose to acute hypoxia, larger body-size adults may be more sensitive to oxygen deficits 38 . ...
Article
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Fish kills, often caused by low levels of dissolved oxygen (DO), involve with complex interactions and dynamics in the environment. In many places the precise cause of massive fish kills remains uncertain due to a lack of continuous water quality monitoring. In this study, we tested if meteorological conditions could act as a proxy for low levels of DO by relating readily available meteorological data to fish kills of grey mullet (Mugil cephalus) using a machine learning technique, the self-organizing map (SOM). Driven by different meteorological patterns, fish kills were classified into summer and non-summer types by the SOM. Summer fish kills were associated with extended periods of lower air pressure and higher temperature, and concentrated storm events 2–3 days before the fish kills. In contrast, non-summer fish kills followed a combination of relatively low air pressure, continuous lower wind speed, and successive storm events 5 days before the fish kills. Our findings suggest that abnormal meteorological conditions can serve as warning signals for managers to avoid fish kills by taking preventative actions. While not replacing water monitoring programs, meteorological data can support fishery management to safeguard the health of the riverine ecosystems.
... There is also evidence that larger individuals are more prone to oxygen limitation in some fish species (Burleson, Wilhelm, & Smatresk, 2001;Robb & Abrahams, 2003;Reid et al., 2013), but it is difficult to generalize this to all fish, given the many different strategies for coping with hypoxia (Chapman & McKenzie, 2009). Indeed, fish may deal with hypoxic stress in a size-dependent manner, with larger animals relying more on anaerobic metabolism (Goolish, 1989;Urbina & Glover, 2013;Lv et al., 2018). On the relatively short timescales typical for hypoxia-tolerance assays, larger fish could supplement their energy needs with anaerobic metabolism; on longer timescales of growth and development, a lower aerobic scope of larger fish in warm waters could reduce growth. ...
Article
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Body size is central to ecology at levels ranging from organismal fecundity to the functioning of communities and ecosystems. Understanding temperature-induced variations in body size is therefore of fundamental and applied interest, yet thermal responses of body size remain poorly understood. Temperature–size (T–S) responses tend to be negative (e.g. smaller body size at maturity when reared under warmer conditions), which has been termed the temperature–size rule (TSR). Explanations emphasize either physiological mechanisms (e.g. limitation of oxygen or other resources and temperature-dependent resource allocation) or the adaptive value of either a large body size (e.g. to increase fecundity) or a short development time (e.g. in response to increased mortality in warm conditions). Oxygen limitation could act as a proximate factor, but we suggest it more likely constitutes a selective pressure to reduce body size in the warm: risks of oxygen limitation will be reduced as a consequence of evolution eliminating genotypes more prone to oxygen limitation. Thus, T–S responses can be explained by the ‘Ghost of Oxygen-limitation Past’, whereby the resulting (evolved) T–S responses safeguard sufficient oxygen provisioning under warmer conditions, reflecting the balance between oxygen supply and demands experienced by ancestors. T–S responses vary considerably across species, but some of this variation is predictable. Body-size reductions with warming are stronger in aquatic taxa than in terrestrial taxa. We discuss whether larger aquatic taxa may especially face greater risks of oxygen limitation as they grow, which may be manifested at the cellular level, the level of the gills and the whole-organism level. In contrast to aquatic species, terrestrial ectotherms may be less prone to oxygen limitation and prioritize early maturity over large size, likely because overwintering is more challenging, with concomitant stronger end-of season time constraints. Mechanisms related to time constraints and oxygen limitation are not mutually exclusive explanations for the TSR. Rather, these and other mechanisms may operate in tandem. But their relative importance may vary depending on the ecology and physiology of the species in question, explaining not only the general tendency of negative T–S responses but also variation in T–S responses among animals differing in mode of respiration (e.g. water breathers versus air breathers), genome size, voltinism and thermally associated behaviour (e.g. heliotherms).
... Given the greater energy yield of aerobic metabolism, we expect anaerobic metabolism (e.g., anaerobic glycolysis) to merely support activity levels above routine metabolic rates for short periods of time, as opposed to completely supporting metabolic expenditure throughout the daytime distribution under hypoxic conditions [17]. However, the large body size of sixgill sharks and consequent lower mass-specific metabolic rate may allow for greater glycogen stores and a slower accumulation of deleterious anaerobic end-products (e.g., lactate and hydrogen ions [H + ]) compared to smaller species [76][77][78]. In addition, sixgill sharks may possess mechanisms for enhanced oxygen extraction and transport, which could enable them to maintain aerobic metabolic rates at the observed low oxygen conditions (i.e., low critical oxygen threshold, P crit ) [17,18]. ...
Article
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Diel vertical migration is a widespread behavioral phenomenon where organisms migrate through the water column and may modify behavior relative to changing environmental conditions based on physiological tolerances. Here, we combined a novel suite of biologging technologies to examine the thermal physiology (intramuscular temperature), fine-scale swimming behavior and activity (overall dynamic body acceleration as a proxy for energy expenditure) of bluntnose sixgill sharks (Hexanchus griseus) in response to environmental changes (depth, water temperature, dissolved oxygen) experienced during diel vertical migrations. In the subtropical waters off Hawai‘i, sixgill sharks undertook pronounced diel vertical migrations and spent considerable amounts of time in cold (5–7°C), low oxygen conditions (10–25% saturation) during their deeper daytime distribution. Further, sixgill sharks spent the majority of their deeper daytime distribution with intramuscular temperatures warmer than ambient water temperatures, thereby providing them with a significant thermal advantage over non-vertically migrating and smaller-sized prey. Sixgill sharks exhibited relatively high rates of activity during both shallow (night) and deep (day) phases and contrary to our predictions, did not reduce activity levels during their deeper daytime distribution while experiencing low temperature and dissolved oxygen levels. This demonstrates an ability to tolerate the low oxygen conditions occurring within the local oxygen minimum zone. The novel combination of biologging technologies used here enabled innovative in situ deep-sea natural experiments and provided significant insight into the behavioral and physiological ecology of an ecologically important deepwater species.
... Our results highlighted that pH decreased with fish weight whereas Lac, Glu and pCO 2 increased. This is in accordance with numerous studies where larger fish are shown to require more energy, resulting in higher secretion of Glu (Barton, 2002), higher production of Lac along with a pCO 2 increase, and a pH decrease (Omlin et al., 2014;Urbina and Glover, 2013). Consequently, blood parameter variations observed throughout the study can result from several phenomena and further research is needed to clarify the importance of each of them. ...
... One species deserves special mention. The inanga (Galaxias maculatus) has been reported to be an oxyconformer in studies that used both closed systems and intermittent-flow systems (Urbina et al., 2012;Urbina and Glover, 2013). The fish is especially interesting because it is scaleless and obtains about 1/3 of its O 2 in normoxic water cutaneously. ...
Article
The critical O2 tension (Pcrit) is the lowest PO2 at which an animal can maintain some benchmark rate of O2 uptake (ṀO2 ). This PO2 has long served as a comparator of hypoxia tolerance in fishes and aquatic invertebrates, but its usefulness in this role, particularly when applied to fishes, has recently been questioned. We believe that Pcrit remains a useful comparator of hypoxia tolerance provided it is determined using the proper methods and hypoxia tolerance is clearly defined. Here, we review the available methods for each of the three steps of Pcrit determination: (1) measuring the most appropriate benchmark ṀO2 state for Pcrit determination (ṀO2,std, the ṀO2 required to support standard metabolic rate); (2) reducing water PO2 ; and (3) calculating Pcrit from the ṀO2 versus PO2 curve. We make suggestions on best practices for each step and for how to report Pcrit results to maximize their comparative value. We also discuss the concept of hypoxia tolerance and how Pcrit relates to a fish's overall hypoxia tolerance. When appropriate methods are used, Pcrit provides useful comparative physiological and ecological information about the aerobic contributions to a fish's hypoxic survival. When paired with other hypoxia-related physiological measurements (e.g. lactate accumulation, calorimetry-based measurements of metabolic depression, loss-of-equilibrium experiments), Pcrit contributes to a comprehensive understanding of how a fish combines aerobic metabolism, anaerobic metabolism and metabolic depression in an overall strategy for hypoxia tolerance.
... Most aquatic organisms maintain a relatively constant oxygen consumption rate with decreasing ambient oxygen concentration until the [O2] crit is reached (Perry et al., 2009;Rogers et al., 2016). There are exceptions such as Inanga (Galaxias maculatus) where oxygen consumption decreases linearly from a normoxic through to a hypoxic environment, indicating that it is a true oxyconformer (Pörtner and Grieshaber, 1993;Urbina and Glover, 2013). Decreasing environmental oxygen past the [O2] crit provokes behavioral (Kramer, 1987), physiological (Barton and Zwama, 1991;Claireaux and Chabot, 2016;Pörtner and Peck, 2010), molecular (Richards, 2009;Soitamo et al., 2001) and genetic (Nikinmaa and Rees, 2005;Wenger, 2000) responses which can help to mitigate oxygen delivery by conserving energy to maintain aerobic ATP production. ...
Article
Low concentrations of dissolved oxygen are one of the most limiting abiotic factors in land-based and marine aquaculture, impacting the welfare of target-species. Yellowtail Kingfish (Seriola lalandi) (YTK) is a high energy demanding species and its commercial aquaculture is rapidly expanding globally yet no information on its hypoxia tolerance is available. YTK is commonly cultured in sea pens, in which abiotic factors such as temperature and ambient oxygen can fluctuate substantially. The move away from marine fish oils to more sustainable terrestrial oil sources in aquafeeds implies a change in fatty acid intake. This shift in fatty acid concentrations and temperature fluctuations can impart physiological effects, impacting the animals stress tolerance. The critical oxygen threshold is a common method to quantify the lower, tolerated threshold of oxygen concentrations for an organism. This study assessed the critical oxygen threshold in fasted, juvenile YTK with respect to acclimation temperature (15 °C & 20 °C) and dietary lipid source (fish oil & poultry oil). Additionally, observations on the visual and behavioral hypoxia responses in YTK were made. This study demonstrated that YTK could regulate their oxygen consumption down to 2.92-1.84 mg dissolved oxygen L-1, but this strongly depends on the acclimation temperature, and to a lesser extent dietary oil source. At dissolved oxygen concentrations below this level, YTK became oxyconformers, unable to maintain an optimum rate of oxygen uptake. Warmer acclimation temperatures led to significantly less hypoxia tolerance compared to YTK held in cooler temperatures. Dietary oil source had no significant effect on the critical oxygen threshold; however, YTK fed a poultry-oil based diet displayed less hypoxia tolerance and greater deviation around the mean, attributing the non-significant difference to YTK fed a fish oil-based diet. Additionally, hypoxia triggered behavioral responses were initiated earlier in YTK fed the poultry oil diet. First behavioral responses, after passing the critical oxygen threshold, were attempted aquatic surface respiration, increased opercular frequency, and gulping, followed by darkening of skin coloration. We recommend rapid oxygenation of the rearing system if dissolved oxygen levels approach 2.92 mg L-1 at 20 °C or at first sign of these changes. Further onset, such as rush or rest behavior, may rapidly lead to the final stages of hypoxia. These results expand knowledge on YTK physiology and behavioral responses to low dissolved oxygen environments and provide information for farm managers to ensure adequate levels of dissolved oxygen throughout rearing, handling, bathing or transportation procedures.
... Water was pumped past the sensor at 50 ml/ min, with the sensor measuring the pO 2 (partial pressure of oxygen) every 2 s. Oxygen electrodes were calibrated daily with fully aerated water (100% oxygen saturation) and a saturated sodium sulfite solution (0% oxygen saturation) (Urbina and Glover, 2013). The second system was a loop to periodically flush the chamber in order to reset the water to the desired pO 2 . ...
Article
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Hypoxia is one of the major threats to biodiversity in aquatic systems. The association of hypoxia with nutrient-rich effluent input into aquatic systems results in scenarios where hypoxic waters could be contaminated with a wide range of chemicals, including metals. Despite this, little is known about the ability of fish to respond to hypoxia when exposures occur in the presence of environmental toxicants. We address this knowledge gap by investigating the effects of exposures to different levels of oxygen in the presence or absence of copper using the three-spined sticklebacks (Gasterosteus aculeatus) model. Fish were exposed to different air saturations (AS; 100%, 75% and 50%) in combination with copper (20 μg/L) over a 4 day period. The critical oxygen level (Pcrit), an indicator of acute hypoxia tolerance, was 54.64 ± 2.51% AS under control conditions, and 36.21 ± 2.14% when fish were chronically exposed to hypoxia (50% AS) for 4 days, revealing the ability of fish to acclimate to low oxygen conditions. Importantly, the additional exposure to copper (20 μg/L) prevented this improvement in Pcrit, impairing hypoxia acclimation. In addition, an increase in ventilation rate was observed for combined copper and hypoxia exposure, compared to the single stressors or the controls. Interestingly, in the groups exposed to copper, a large increase in variation in the measured Pcrit was observed between individuals, both under normoxic and hypoxic conditions. This variation, if observed in wild populations, may lead to selection for a tolerant phenotype and alterations in the gene pool of the populations, with consequences for their sustainability. Our findings provide strong evidence that copper reduces the capacity of fish to respond to hypoxia by preventing acclimation and will inform predictions of the consequences of global increases of hypoxia in water systems affected by other pollutants worldwide.
Preprint
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Global warming appears to favour smaller-bodied organisms, but whether larger species are also more vulnerable to thermal extremes, as suggested for past mass-extinction events, is still an open question. Here, we tested whether interspecific differences in thermal tolerance (heat and cold) of ectotherm organisms are linked to differences in their body mass and genome size (as a proxy for cell size). Since the vulnerability of larger, aquatic taxa to warming has been attributed to the oxygen limitation hypothesis, we also assessed how body mass and genome size modulate thermal tolerance in species with contrasting breathing modes, habitats and life stages. A database with the upper (CTmax) and lower (CTmin) critical thermal limits and their methodological aspects was assembled comprising more than 500 species of ectotherms. Our results demonstrate that thermal tolerance in ectotherms is dependent on body mass and genome size and these relationships became especially evident in prolonged experimental trials where energy efficiency gains importance. During long-term trials, CTmax was impaired in larger-bodied water-breathers, consistent with a role for oxygen limitation. Variation in CTmin was mostly explained by the combined effects of body mass and genome size and it was enhanced in larger-celled, air-breathing species during long-term trials, consistent with a role for depolarization of cell membranes. Our results also highlight the importance of accounting for phylogeny and exposure duration. Especially when considering long-term trials, the observed effects on thermal limits are more in line with the warming-induced reduction in body mass observed during long-term rearing experiments. This article is part of the theme issue ‘Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen’.
Article
The capacity of fishes to tolerate low oxygen (hypoxia) through behavioral and physiological adjustments varies among species in a fashion that correlates with oxygen availability in their natural habitats. Less is known about variation in hypoxia tolerance within a species, but it is expressly this interindividual variation that will determine which individuals will survive during severe hypoxia. Here, we measured aquatic surface respiration (ASR) and loss of equilibrium (LOE), two common indexes of hypoxia tolerance of fishes, in gulf killifish, Fundulus grandis, subjected to multiple trials of a highly reproducible hypoxia protocol over a period of 6-8 wk. The time and [Formula: see text] at the first occurrence of ASR and the time and [Formula: see text] at LOE differed significantly among individuals in a repeatable fashion. This interindividual variation in ASR and LOE was significantly correlated with general body and gill morphology. The time to ASR was shorter and the [Formula: see text] at ASR was higher for fish with greater mass. After correcting for mass, fish with longer or more numerous gill filaments had longer times to ASR or LOE, respectively. Fish in better condition factor (heavier for their length) had lower [Formula: see text] at LOE. Repeatable interindividual variation in hypoxia tolerance, if genetically based, could influence the capacity of species to adapt as their habitats become increasingly threatened by aquatic hypoxia.
Preprint
This study characterised selected peripheral blood (PB) haematological parameters, liver, serum and muscle metabolic features in three‐ and five‐year old male and female giant kokopu (Galaxias argenteus) broodstock reared indoor at 16°C. Sex and age did not affect PB total cell count, and haematocrit values. However, higher erythrocytes in five‐year old fish, elevated thrombocyte and lymphocyte counts in three‐year old fish indicate age‐specific cellular regulation. Higher thrombocyte counts in female fish suggest sex‐specific regulation. At a metabolic level, liver abundance for long chain saturated fatty acids were higher in males, while females had elevated levels of polyunsaturated fatty acids. Essential and non‐essential amino acids in liver and serum were also elevated in females compared to males. These findings suggest differential allocation of fatty acids and amino acids to reflect requirements for gonadal, development and provisioning. Similarly, age significantly resulted in higher liver and serum abundances of some non‐essential amino acids in three‐year olds compared to five‐year old fish, suggesting higher metabolism in younger fish. Overall, results enhance our understanding of sex‐ and age‐based differences in fish haematology, muscle, liver, and serum metabolite profiles in healthy G. argenteus. Future studies should carefully consider potential age‐ and sex‐specific differences in metabolic responses. This article is protected by copyright. All rights reserved.
Article
This study characterised selected peripheral blood (PB) haematological parameters, liver, serum and muscle metabolic features in three‐ and five‐year old male and female giant kokopu (Galaxias argenteus) broodstock reared indoor at 16°C. Sex and age did not affect PB total cell count, and haematocrit values. However, higher erythrocytes in five‐year old fish, elevated thrombocyte and lymphocyte counts in three‐year old fish indicate age‐specific cellular regulation. Higher thrombocyte counts in female fish suggest sex‐specific regulation. At a metabolic level, liver abundance for long chain saturated fatty acids were higher in males, while females had elevated levels of polyunsaturated fatty acids. Essential and non‐essential amino acids in liver and serum were also elevated in females compared to males. These findings suggest differential allocation of fatty acids and amino acids to reflect requirements for gonadal, development and provisioning. Similarly, age significantly resulted in higher liver and serum abundances of some non‐essential amino acids in three‐year olds compared to five‐year old fish, suggesting higher metabolism in younger fish. Overall, results enhance our understanding of sex‐ and age‐based differences in fish haematology, muscle, liver, and serum metabolite profiles in healthy G. argenteus. Future studies should carefully consider potential age‐ and sex‐specific differences in metabolic responses.
Article
Individual striped bass Morone saxatilis were each exposed in random order to aquatic hypoxia (10% air saturation) either while swimming at 50% of their estimated critical swimming speed (Ucrit ) or while at rest until they lost equilibrium. Individuals were always less tolerant of hypoxia when swimming (P < 0·01); the average fish was over five times more tolerant to the same hypoxia exposure when not swimming. There was no relationship between an individual's rank order of hypoxia tolerance (HT) under the two flow regimes, suggesting that different factors determine an individual's HT when at rest than when swimming. © 2015 The Fisheries Society of the British Isles.
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Global warming appears to favour smaller-bodied organisms, but whether larger species are also more vulnerable to thermal extremes, as suggested for past mass-extinction events, is still an open question. Here, we tested whether interspecific differences in thermal tolerance (heat and cold) of ectotherm organisms are linked to differences in their body mass and genome size (as a proxy for cell size). Since the vulnerability of larger, aquatic taxa to warming has been attributed to the oxygen limitation hypothesis, we also assessed how body mass and genome size modulate thermal tolerance in species with contrasting breathing modes, habitats and life stages. A database with the upper (CTmax) and lower (CTmin) critical thermal limits and their methodological aspects was assembled comprising more than 500 species of ectotherms. Our results demonstrate that thermal tolerance in ectotherms is dependent on body mass and genome size and these relationships became especially evident in prolonged experimental trials where energy efficiency gains importance. During long-term trials, CTmax was impaired in larger-bodied water-breathers, consistent with a role for oxygen limitation. Variation in CTmin was mostly explained by the combined effects of body mass and genome size and it was enhanced in larger-celled, air-breathing species during long-term trials, consistent with a role for depolarization of cell membranes. Our results also highlight the importance of accounting for phylogeny and exposure duration. Especially when considering long-term trials, the observed effects on thermal limits are more in line with the warming-induced reduction in body mass observed during long-term rearing experiments. This article is part of the theme issue ‘Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen’.
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Global warming appears to favour smaller-bodied organisms, but whether larger species are also more vulnerable to thermal extremes, as suggested for past mass-extinction events, is still an open question. Here, we tested whether interspecific differences in thermal tolerance (heat and cold) of ectotherm organisms are linked to differences in their body mass and genome size (as a proxy for cell size). Since the vulnerability of larger, aquatic taxa to warming has been attributed to the oxygen limitation hypothesis, we also assessed how body mass and genome size modulate thermal tolerance in species with contrasting breathing modes, habitats and life-stages. A database with the upper (CTmax) and lower (CTmin) critical thermal limits and their methodological aspects was assembled comprising more than 500 species of ectotherms. Our results demonstrate that thermal tolerance in ectotherms is dependent on body mass and genome size and these relationships became especially evident in prolonged experimental trials where energy efficiency gains importance. During long-term trials, CTmax was impaired in larger-bodied water-breathers, consistent with a role for oxygen limitation. Variation in CTmin was mostly explained by the combined effects of body mass and genome size and it was enhanced in larger-celled, air-breathing species during long-term trials, consistent with a role for depolarization of cell membranes. Our results highlight the importance of accounting for phylogeny and exposure duration. Especially when considering long-term trials, the observed effects on thermal limits are more in line with the warming-induced reduction in body mass observed during long-term rearing experiments.
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Body size and temperature are primary determinants of metabolic rate, and the standard metabolic rate (SMR) of animals ranging in size from unicells to mammals has been thought to be proportional to body mass (M) raised to the power of three-quarters for over 40 years. However, recent evidence from rigorously selected datasets suggests that this is not the case for birds and mammals. To determine whether the influence of body mass on the metabolic rate of vertebrates is indeed universal, we compiled SMR measurements for 938 species spanning six orders of magnitude variation in mass. When normalized to a common temperature of 38 degrees C, the SMR scaling exponents of fish, amphibians, reptiles, birds and mammals are significantly heterogeneous. This suggests both that there is no universal metabolic allometry and that models that attempt to explain only quarter-power scaling of metabolic rate are unlikely to succeed.
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Ectotherms distributed along environmental gradients often show marked variation in physiological and life-history traits. Different life-history phenotypes may be correlated with variations in maintenance metabolism. We measured life-history traits and metabolic rate (VO2) of the common wood louse (Porcellio laevis Latreille, 1804) from a lowland population and a highland population in northern Chile. We measured VO2 at 5, 12, 18, and 25°C. Wood lice from different altitudes exhibited large variations in life-history traits, which were correlated with changes in VO2. Fecundity of wood lice decreased and egg volume, offspring size, and reproductive output of females increased in highland populations compared with lowland populations. Isopods from the highland had a higher VO2 than those from lowland habitats for almost all temperatures. However, when we considered VO2 at 5°C, VO2 was lowest in the high-altitude isopods. In addition, since the highest thermal sensitivity values in the VO2-temperature curves were found at the lowest and highest temperature ranges for the highland population rather than for the lowland population, our study did not support the metabolic cold-adaptation hypothesis. We concluded that differences in VO2 between the populations contributed to the difference in reproductive output by wood lice from cold and warm habitats.
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Metabolic cold adaptation (MCA), the hypothesis that species from cold climates have relatively higher metabolic rates than those from warm climates, was first proposed nearly 100 years ago and remains one of the most controversial hypotheses in physiological ecology. In the present study, we test the MCA hypothesis in fishes at the level of whole animal, mitochondria and enzyme. In support of the MCA hypothesis, we find that when normalized to a common temperature, species with ranges that extend to high latitude (cooler climates) have high aerobic enzyme (citrate synthase) activity, high rates of mitochondrial respiration and high standard metabolic rates. Metabolic compensation for the global temperature gradient is not complete however, so when measured at their habitat temperature species from high latitude have lower absolute rates of metabolism than species from low latitudes. Evolutionary adaptation and thermal plasticity are therefore insufficient to completely overcome the acute thermodynamic effects of temperature, at least in fishes.
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Thermal limits may arise through a mismatch between oxygen supply and demand in a range of animal taxa. Whilst this oxygen limitation hypothesis is supported by data from a range of marine fish and invertebrates, its generality remains contentious. In particular, it is unclear whether oxygen limitation determines thermal extremes in tracheated arthropods, where oxygen limitation may be unlikely due to the efficiency and plasticity of tracheal systems in supplying oxygen directly to metabolically active tissues. Although terrestrial taxa with open tracheal systems may not be prone to oxygen limitation, species may be affected during other life-history stages, particularly if these rely on diffusion into closed tracheal systems. Furthermore, a central role for oxygen limitation in insects is envisaged within a parallel line of research focussing on insect gigantism in the late Palaeozoic. Here we examine thermal maxima in the aquatic life stages of an insect at normoxia, hypoxia (14 kPa) and hyperoxia (36 kPa). We demonstrate that upper thermal limits do indeed respond to external oxygen supply in the aquatic life stages of the stonefly Dinocras cephalotes, suggesting that the critical thermal limits of such aquatic larvae are set by oxygen limitation. This could result from impeded oxygen delivery, or limited oxygen regulatory capacity, both of which have implications for our understanding of the limits to insect body size and how these are influenced by atmospheric oxygen levels. These findings extend the generality of the hypothesis of oxygen limitation of thermal tolerance, suggest that oxygen constraints on body size may be stronger in aquatic environments, and that oxygen toxicity may have actively selected for gigantism in the aquatic stages of Carboniferous arthropods.
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Hypoxia has significant effects on organisms, from metabolic reduction to death, and could be an important evolutionary force affecting the variation among populations within a species. To determine intraspecific variation in hypoxic metabolism and the effect of body mass, we examine rates of oxygen consumption (M(O2)) at seven oxygen concentrations among seven populations of Fundulus grandis that inhabit a mosaic of habitats with different frequencies and intensities of hypoxia. For M(O2), there is a significant interaction (P< 0.05) between body mass and oxygen concentrations: log(10) body mass: log(10) M(O2) slopes were steeper at intermediate oxygen partial pressures (Po(2)) than either normoxic or lowest Po(2) (ANCOVA, P<0.001). Additionally, the PO(2crit) (Po(2) where M(O2) can no longer be maintained) was a negative function of body mass (P < 0.04). At the lowest Po(2) (1.8 kPa), there was a significant difference in M(O2) among populations: one of the populations from environments more frequently stressed by hypoxia has greater M(O2) at the lowest oxygen concentrations. With few differences among populations, the most important effects were how body mass affected M(O2) at intermediate Po(2) and the negative relationship between body mass and PO(2crit). These findings suggest that an increase in body size is a useful strategy to minimize the effect of hypoxia.
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Water quality in agricultural catchments tends to be worse than in forested (native or exotic) catchments. Reduced water quality tends to have significant effects on the ecosystem of streams, including increased nuisance algal and plant growth (eutrophication) associated with nutrient input, toxicity to aquatic life due to ammonia, faecal contamination, and loss of habitat or spawning areas due to sedimentation. An analysis of catchment contaminant loads from 38 studies conducted since 1975 was carried out to determine if there were differences in loads between land uses under different livestock (dairy, sheep, sheep-and-beef (mixed), deer) and non-agricultural. Significantly more N was lost from dairy catchments than catchments with other land uses, and more sediment lost from deer catchments than other catchments. Median loads of N were greatest from dairy > deer = mixed > sheep > non-agricultural; while loads of P were greatest for deer = mixed > dairy > sheep > non-agricultural; and for sediment, deer > sheep > mixed > dairy > non-agricultural. This information should be considered in catchments of mixed stock types to target the most pertinent mitigation practice for improving water quality. For example, if a stream in a catchment with deer and sheep present is choked with algae and limited by inputs of P, mitigation should focus on deer rather than sheep.
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Allometric scaling relations, including the 3/4 power law for metabolic rates, are characteristic of all organisms and are here derived from a general model that describes how essential materials are transported through space-filling fractal networks of branching tubes. The model assumes that the energy dissipated is minimized and that the terminal tubes do not vary with body size. It provides a complete analysis of scaling relations for mammalian circulatory systems that are in agreement with data. More generally, the model predicts structural and functional properties of vertebrate cardiovascular and respiratory systems, plant vascular systems, insect tracheal tubes, and other distribution networks.
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The relationship between mammalian basal metabolic rate (BMR, ml of O(2) per h) and body mass (M, g) has been the subject of regular investigation for over a century. Typically, the relationship is expressed as an allometric equation of the form BMR = aM(b). The scaling exponent (b) is a point of contention throughout this body of literature, within which arguments for and against geometric (b = 2/3) and quarter-power (b = 3/4) scaling are made and rebutted. Recently, interest in the topic has been revived by published explanations for quarter-power scaling based on fractal nutrient supply networks and four-dimensional biology. Here, a new analysis of the allometry of mammalian BMR that accounts for variation associated with body temperature, digestive state, and phylogeny finds no support for a metabolic scaling exponent of 3/4. Data encompassing five orders of magnitude variation in M and featuring 619 species from 19 mammalian orders show that BMR proportional, variant M(2/3).
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Using respirometry, we examined the hypoxia tolerance of 31 teleost fish species (seven families) inhabiting coral reefs at a 2-5 m depth in the lagoon at Lizard Island (Great Barrier Reef, Australia). All fishes studied maintained their rate of oxygen consumption down to relatively severe hypoxia (20-30% air saturation). Indeed, most fishes appeared unaffected by hypoxia until the oxygen level fell below 10% of air saturation. This, hitherto unrecognized, hypoxia tolerance among coral reef fishes could reflect adaptations to nocturnal hypoxia in tide pools. It may also be needed to enable fishes to reside deep within branching coral at night to avoid predation. Widespread hypoxia tolerance in a habitat with such an extreme biodiversity as coral reefs indicate that there is a wealth of hypoxia related adaptations to be discovered in reef fishes.
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The field metabolic rates (FMRs) of 229 species of terrestrial vertebrates, all measured using the doubly labeled water method in free-living individuals, were evaluated. Daily rates of energy expenditure were as low as 0.23 kJ per day in a small reptile (gecko), to as high as 52 500 kJ per day in a marine mammal (seal). This is a range of nearly six orders of magnitude. More than 70% of the variation in log-transformed data is due to variation in body size (expressed as body mass). Much of the remaining variation is accounted for by thermal physiology, with the endothermic mammals and birds having FMRs that are about 12 and 20 times higher, respectively, than FMRs of equivalent-sized, but ectothermic, reptiles. Variation in log(body mass) within each of these three taxonomic classes accounts for over 94% of the variation in log(FMR), and results from nonlinear regression analyses using untransformed data support this conclusion. However, the range of residual variation in mass-adjusted FMR within classes is still more than sixfold (ratio of highest over lowest). Some of this variation is associated with affiliations with lower taxonomic levels (Infraclass: eutherian vs metatherian mammals; Family: passerine, procellariform and galliform birds vs other birds), some is associated with habitat (especially desert vs nondesert), and some with differences in basic diet preference and foraging mode and season. The scaling slopes for FMR often differ from BMR slopes for the same Class of animals, and most differ from the theoretical slope of 0.75. Differences among slopes and intercepts that were detected using conventional regression analyses were largely confirmed upon reanalysis using Independent Contrasts Analysis to adjust for phylogenetic biases.
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The physiological and behavioural responses of two size groups of oscar (Astronotus ocellatus) to hypoxia were studied. The physiological responses were tested by measuring M(O(2)) during decreasing environmental oxygen tensions. Larger oscars were better able to maintain oxygen consumption during a decrease in P(O(2)), regulating routine M(O(2)) to a significantly lower P(O(2)) threshold (50 mmHg) than smaller oscars (70 mmHg). Previous studies have also demonstrated a longer survival time of large oscars exposed to extreme hypoxia, coupled with a greater anaerobic enzymatic capability. Large oscars began aquatic surface respiration (ASR) at the oxygen tension at which the first significant decrease in M(O(2)) was seen (50 mmHg). Interestingly, smaller oscars postponed ASR to around 22 mmHg, well beyond the P(O(2)) at which they switched from oxyregulation to oxyconformation. Additionally, when given the choice between an hypoxic environment containing aquatic macrophyte shelter and an open normoxic environment, small fish showed a greater preference for the hypoxic environment. Thus shelter from predators appears particularly important for juveniles, who may accept a greater physiological compromise in exchange for safety. In response to hypoxia without available shelter, larger fish reduced their level of activity (with the exception of aggressive encounters) to aid metabolic suppression whereas smaller oscars increased their activity, with the potential benefit of finding oxygen-rich areas.
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Understanding the local and regional patterns of species distributions has been a major goal of ecological and evolutionary research. The notion that these patterns can be understood through simple quantitative rules is attractive, but while numerous scaling laws exist (e.g., metabolic, fractals), we are aware of no studies that have placed individual traits and community structure together within a genetics based scaling framework. We document the potential for a genetic basis to the scaling of ecological communities, largely based upon our long-term studies of poplars (Populus spp.). The genetic structure and diversity of these foundation species affects riparian ecosystems and determines a much larger community of dependent organisms. Three examples illustrate these ideas. First, there is a strong genetic basis to phytochemistry and tree architecture (both above- and belowground), which can affect diverse organisms and ecosystem processes. Second, empirical studies in the wild show that the local patterns of genetics based community structure scale up to western North America. At multiple spatial scales the arthropod community phenotype is related to the genetic distance among plants that these arthropods depend upon for survival. Third, we suggest that the familiar species-area curve, in which species richness is a function of area, is also a function of genetic diversity. We find that arthropod species richness is closely correlated with the genetic marker diversity and trait variance suggesting a genetic component to these curves. Finally, we discuss how genetic variation can interact with environmental variation to affect community attributes across geographic scales along with conservation implications.
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Hypoxia represents a significant challenge to most fish, forcing the development of behavioural, physiological and biochemical adaptations to survive. It has been previously shown that inanga (Galaxias maculatus) display a complex behavioural repertoire to escape aquatic hypoxia, finishing with the fish voluntarily emerging from the water and aerially respiring. In the present study we evaluated the physiological, metabolic and biochemical consequences of both aquatic hypoxia and emersion in inanga. Inanga successfully tolerated up to 6 h of aquatic hypoxia or emersion. Initially, this involved enhancing blood oxygen-carrying capacity, followed by the induction of anaerobic metabolism. Only minor changes were noted between emersed fish and those maintained in aquatic hypoxia, with the latter group displaying a higher mean cell haemoglobin content and a reduced haematocrit after 6 h. Calculations suggest that inanga exposed to both aquatic hypoxia and air reduced oxygen uptake and also increased anaerobic contribution to meet energy demands, but the extent of these changes was small compared with hypoxia-tolerant fish species. Overall, these findings add to previous studies suggesting that inanga are relatively poorly adapted to survive aquatic hypoxia.
Article
The objectives of the present study were to determine, for Nile tilapia of different body weights and fed to satiation, (1) the incipient dissolved oxygen (DO) concentration at which feed intake starts to level off and (2) the effect of DO on nitrogen and energy balances. Two successive experiments were conducted with two weight classes of male Nile tilapia (>200 g, Experiment 1, and <100 g, Experiment 2). Twelve aquaria were assigned to four DO levels in each experiment. Fish were fed to apparent satiation for 16 and 20 days in Experiments 1 and 2 respectively. The DO-feed intake curve of fish<100 g appeared to level off at a DO of 3 mg L−1, while that of fish>200 g continued to increase as DO increased from 2.6 to 6.0 mg L−1. The latter curve suggests that the incipient DO for fish>200 g is about 5.5 mg L−1. Fish tended to reduce the energy requirement for maintenance as DO declined. A DO reduction caused an increase in the apparent digestibility coefficient (ADC), but further declines in DO to levels below a critical level decreased ADC. The DO did not have a considerable effect on the metabolizable energy: digestible energy ratio of the diet.
Data
Galaxias maculatus is an osmeriform native ¢sh of the Southern Hemisphere, in which the crystalline lar-vae is considered as a luxury delicacy, for this reason, it has been commercially exploited in Chile, Argenti-na and New Zealand. However, the ¢sheries have been rapidly decreasing due to the overexploitation and the predation of introduced species. Because of these events, there is a need to determine a carrying capacity for an intensive ¢sh culture. In order to opti-mize stocking densities for ¢sh culture, this paper proposes objectives to determine oxygen consump-tion (OC) rates, dissolved oxygen concentrations that produce signs of hypoxia and the average time elapsed between food intake and peak OC in G. macu-latus. In the oxygen experiments under routine meta-bolism conditions, we found that G. maculatus adults and whitebait showed signs of asphyxia at dissolved oxygen concentrations between 1.3 and 2.2 mg L À 1 and that adults tolerated dissolved oxygen levels as low as1.3 mg L À 1 . The results showed that G. macula-tus individuals with an average weight of 0.04 g con-sumed 0.048 mg O 2 h À 1 , whereas individuals with an average weight of 1.4 g consumed 0.345 mg O 2 h À 1 . Galaxias maculatus increased the OC rate by 31%, from 0.39 to 0.51mg O 2 h À 1 g À 1 , occurring 14 min after food intake. The carrying capacities for industrial cultures of G. maculatus, were estimated using an allometric equation (OC 50.2363 Â W 0.612), a water £ow rate of 1m 3 h À 1 and an input oxygen concentration of 10 mg L À 1 at 12 1C. The density culture of whitebait (4 g) can be allowed to reach 8^11kg m À 3 ; therefore, these stocking densities reduce the risk of hypoxia and mortality, ensuring the appropriate growth and feed conversion rates.
Article
Fish, like other living systems, must conform to the laws of thermodynamics. Fish gain matter and energy in food, and they lose absorbed matter and energy as a result of catabolism—which provides energy for maintenance and activity—and the elaboration of reproductive products. Physiological energetics, or animal bioenergetics, concerns the rates of energy expenditure, the losses and gains, and the efficiencies of energy transformation, as functional relations of the whole organism. The majority of such presentations commence with an energy-flow diagram indicating the main steps that the energy of food intake follows through the organism, and the paths of energy distribution. Each of these steps with their appropriate values is subject to quantitative change, depending on many biotic and abiotic factors. With the thought that the basis of these energy exchanges needs to be elaborated first, it was deemed more fitting to conclude with a quantitatively expressed flow diagram. An understanding of the physical, chemical, and biological basis on which the energetics is built, and the equivalents employed, constitutes the opening section of this chapter. Some necessary distinctions between mammalian and nonmammalian systems are made. An adequately nutritious diet is assumed; the basic source of fuel for the fire of life is solely derived from the food.
Article
This chapter discusses the effect of body size on metabolism in fishes. There are no obvious direct effects of body size on cell metabolism because the size of individual cells remains relatively unchanged. With larger body size, cellular metabolism is increasingly removed from the environment by distance, and therefore also by time. The distancing between the cell and environment that occurs with increased body size will result in a decreased rate of delivery of these limiting factors. The chapter discusses the way discuss this limitation in the delivery of materials can be expected to influence the physiology and cellular metabolism of fish. It presents theoretical explanations for the negative allometry of aerobic metabolism and analyzes the scaling of maximum whole-body aerobic capacity. The chapter also describes symmorphosis and the scaling of individual respiratory traits and elaborates the effects of body size on anaerobic metabolism.
Article
The tolerances of seven New Zealand freshwater fish species and one species of shrimp to low levels of dissolved oxygen were determined in the laboratory by holding fish at dissolved oxygen levels of 1, 3, or 5 mg litre for 48 h at 15°C. Juvenile rainbow trout (Oncorhynchus mykiss) were also tested for comparison. All of the banded kokopu whitebait (Galaxias fasciatus), juvenile torrentfish (Cheimarrichthys fosteri), adult and juvenile common smelt (Retropinna retropinna), juvenile common bully (Gobiomorphus cotidianus), and trout were dead after 48 h exposure to 1 mg litre. Adult and juvenile inanga (Galaxias maculatus), adult common bully (Gobiomorphus cotidianus), and shrimp (Paratya curvirostris) had mortalities ranging from 27 to 80% at 1 mg litre, whereas all of the elvers (Anguilla spp.) survived. Juvenile rainbow trout were the most sensitive of the species tested, and the only species that had mortalities during exposure to 3 mg litre. No deaths of any fish occurred at 5 mg litre. Time to 50% mortality at 1 mg litre for common smelt (adult and juvenile) and juvenile common bully were similar to those for juvenile rainbow trout. Most fish moved towards the surface within the first few hours of exposure to 1 mg litre. Rainbow trout was the only species that showed consistent surfacing behaviour at 3 mg litre and rarely were fish observed to move towards the surface at 5 mg litre. Within the limits of the lifestages and species tested, adequate protection is provided for native fish by adopting the United States Environmental Protection Agency dissolved oxygen criteria for salmonid waters.
Article
The rate of oxygen consumption of individual males of Enoplus brevis and E. communis was measured at 15° C and at each of four oxygen tensions, 135, 75, 35, and 12 Torr, after at least 12 hr experience of the conditions. It was demonstrated that the level of oxygen consumption of both species was reduced by each lowering of the imposed oxygen tension. The oxygen consumption of each species fell with increasing body size. On a unit dry weight basis the oxygen consumption of E. brevis is greater than that of the larger E. communis, but after allowing for the difference of body size the two species have more or less similar oxygen uptakes at all oxygen tensions. In E. brevis oxygen tension influenced the relationship of body size and metabolism, the slope relating oxygen consumption and body weight becomes steeper with decreasing oxygen tension. This effect was not shown by E. communis. Some general factors influencing the availability of oxygen to nematodes are considered.
Article
The respiratory behaviour of the sharpsnout sea bream (Diplodus puntazzo) with fish weights between 15 and 509 g at temperatures of 15–29°C was studied, with special attention paid to critical and lethal oxygen saturation (Scrit and LC50, respectively) and ventilatory frequency (Vf). The species maintained a constant oxygen consumption rate regardless of the concentration of dissolved oxygen, until Scrit was reached. The mean of Scrit and LC50 was 34% (2.4 mg L−1) and 11% (0.8 mg L−1), respectively. The Scrit was independent of fish weight and temperature, whereas the LC50 values were positively correlated with both factors (P < 0.05). The higher resistance in small fish could be due to their greater Vf response to hypoxia than in larger animals. Furthermore, the increased metabolism resulting from the effect of temperature was offset by an increased Vf. The Vf remained constant down to a mean value of 67% oxygen saturation, regardless of fish weight and temperature. These findings suggest an optimum oxygen saturation of above 70% for D. puntazzo culture.
Article
Three physiological variables, haematocrit, haemoglobin concentration and ventilation frequency, were measured to test how fathead minnows Pimephales promelas and small and large yellow perch Perca flavescens responded to three different dissolved oxygen concentrations. All fish were monitored continuously for any indications of stress in response to these manipulations. Within and between species, smaller individuals were the most tolerant of hypoxic environments. A species effect, however, did contribute to this observation, with fathead minnows being more tolerant of hypoxic environments than similar-sized yellow perch. In aquatic ecosystems where smaller fishes are more tolerant to hypoxia than their larger predators, hypoxic environments may have the potential to act as a refuge from predators.
Article
When an oxygen gradient ranging from c. 10 to 95% air saturation was formed in a 5 m chamber, largemouth bass Micropterus salmoides avoided water in which dissolved oxygen values were <27% air saturation. There was a significant (P<0·05) correlation between fish mass and the level of dissolved aquatic oxygen that was selected. Small fish (23–500 g) utilized waters of lower oxygen levels than did the larger fish (1000–3000 g). The results of this study suggest that largemouth bass are able to sense and avoid hypoxic water, and select aquatic oxygen tensions that maintain their metabolic scope for growth and activity.
Article
The growth of commercial aquaculture in Chile generated an income of $2.300 million USD in exports in 2005. Currently, 15 different species are cultivated commercially, of which seven are native; these had returns of 185 million USD. Among these native species is Galaxias maculatus (whitebait), which is endemic to Chile and figures significantly in Chilean fishing statistics. Since the 1990s, the School of Aquaculture of the Universidad Catolica de Temuco has been developing cultivation of this native species. This work presents the state of the art of the cultivation of this fish.
Article
AimThis study seeks evidence for coevolution between the galaxioid fish families, Galaxiidae and Retropinnidae, and their macroparasites as a means of adding to our understanding of the biogeography of the fish families.LocationThese families are characteristic southern cool-temperate elements in the fish faunas of Australia, New Zealand and southern South America and some southern/sub-Antarctic islands.Methods The analysis is based on a review of the literature.ResultsAnalysis showed that in each area fish species have parasites that are representative of the general fish parasite faunas of that area, rather than those characteristic of, or specific to, either these galaxioid families or the genera and species that they contain. In many instances the parasites also infect exotic fish species introduced into each area.Main conclusionsThere is little evidence that parasite faunas have coevolved with the fish hosts. Parasite data therefore provide little support for a vicariance biogeography of galaxioid fishes in the southern cool-temperate region. Also, the data do not conflict with dispersal hypotheses for that biogeography.
Article
1. We examined published studies relating resting oxygen consumption to body mass and temperature in post-larval teleost fish. The resulting database comprised 138 studies of 69 species (representing 28 families and 12 orders) living over a temperature range of c. 40 °C. 2. Resting metabolic rate (Rb; mmol oxygen gas h–1) was related to body mass (M; wet mass, g) by Rb = aMb, where a is a constant and b the scaling exponent. The model was fitted by least squares linear regression after logarithmic transformation of both variables. The mean value of scaling exponent, b, for the 69 individual species was 0·79 (SE 0·11). The general equation for all teleost fish was 1nRb = 0·80(1nM) – 5·43. 3. The relationship between resting oxygen consumption and environmental temperature for a 50-g fish was curvilinear. A typical tropical fish at 30°C requires approximately six times as much oxygen for resting metabolism as does a polar fish at 0°C. This relationship could be fitted by several statistical models, of which the Arrhenius model is probably the most appropriate. The Arrhenius model for the resting metabolism of 69 species of teleost fish, corrected to a standard body mass of 50 g, was 1nRb = 15·7 – 5·02.T–1, where T is absolute temperature (103 × K). 4. The Arrhenius model fitted to all 69 species exhibited a lower thermal sensitivity of resting metabolism (mean Q10 = 1·83 over the range 0–30 °C) than typical within-species acclimation studies (median Q10 = 2·40, n = 14). This suggests that evolutionary adaptation has reduced the overall thermal sensitivity of resting metabolism across species. Analysis of covariance indicated that the relationships between resting metabolic rate and temperature for various taxa (orders) showed similar slopes but significantly different mean rates. 5. Analysis of the data for perciform fish provided no support for metabolic cold adaptation (the hypothesis that polar fish show a resting metabolic rate higher than predicted from the overall rate/temperature relationship established for temperate and tropical species). 6. Taxonomic variation in mean resting metabolic rate showed no relationship to phylogeny, although the robustness of this conclusion is constrained by our limited knowledge of fish evolutionary history.
Chapter
It is generally recognized that larger animals eat more, live longer, have larger offspring, and so on; but it is unusual to see these commonplace observations as a basis for scientific biology. A large number of empirically based relationships describe biological rates as simple functions of body size; and other such relations predict the intrinsic rate of population growth, animal speed, animal density, territory size, prey size, physiology, and morphology. Such equations almost always exist for mammals and birds, often for other vertebrates and invertebrates, sometimes for protozoa, algae, and bacteria, and occasionally even for plants. There are too many organisms to measure all aspects of the biology of every species of population, so scientists must depend on generalizations. Body size relations represent our most extensive and powerful assemblage of generalizations, but they have never been organized for use in ecology. This book represents the largest single compilation of interspecific size relations, and instructs the reader on the use of these relationships; their comparison, combination, and criticism. Both strengths and weaknesses of our current knowledge are discussed in order to indicate the many possible directions for further research. This important volume will therefore provide a point of departure toward a new applied ecology, giving quantitative solutions to real questions. It will interest advanced students of ecology and comparative physiology as well as professional biologists.
Article
Expanding upon a preliminary communication (Nature 417 (2002) 166), we here further develop a 'multiple-causes model' of allometry, where the exponent b is the sum of the influences of multiple contributors to control. The relative strength of each contributor, with its own characteristic value of b(i), is determined by c(i), the control contribution or control coefficient. A more realistic equation for the scaling of metabolism with body size thus can be written as BMR=MR(0)Sigmac(i)(M/M-0)(bi), where MR0 is the 'characteristic metabolic rate' of an animal with a 'characteristic body mass', M-0. With M-0 of 1 unit mass (usually kg), MR0 takes the place of the value a, found in the standard scaling equation, bi is the scaling exponent of the process i, and c(i) is its control contribution to overall flux, or the control coefficient of the process i. One can think of this as an allometric cascade, with the b exponent for overall energy metabolism being determined by the b(i) and c(i) values for key step
Article
In this review I show that the ‘3/4-power scaling law’ of metabolic rate is not universal, either within or among animal species. Significant variation in the scaling of metabolic rate with body mass is described mainly for animals, but also for unicells and plants. Much of this variation, which can be related to taxonomic, physiological, and/or environmental differences, is not adequately explained by existing theoretical models, which are also reviewed. As a result, synthetic explanatory schemes based on multiple boundary constraints and on the scaling of multiple energy-using processes are advocated. It is also stressed that a complete understanding of metabolic scaling will require the identification of both proximate (functional)and ultimate (evolutionary)causes. Four major types of intraspecific metabolic scaling with body mass are recognized [based on the power function R=aMb, where R is respiration (metabolic) rate, a is a constant, M is body mass, and b is the scaling exponent]: Type I: linear, negatively allometric (b
Article
Summary 1. A long-standing theoretical problem in biology is the relation between organism size M and metabolic rate Q. 2. This long history of research into such a basic pattern is due to the particular shape of the relationship: it is generally observed that the relation is well described as QMb where b is most often between 0.5 and 1. 3. Numerous analyses have focused on determining b using interspecific data, in particular to test whether b=2/3 or b=3/4. 4. Here a large amount of intraspecific data on fish are analysed, which show that bne2/3, bne3/4, and especially that there is no single, universal value of b.
Article
During the 13 years since it was first advanced, the fractal network theory (FNT), an analytic theory of allometric scaling, has been subjected to a wide range of methodological, mathematical and empirical criticisms, not all of which have been answered satisfactorily. FNT presumes a two-variable power-law relationship between metabolic rate and body mass. This assumption has been widely accepted in the past, but a growing body of evidence during the past quarter century has raised questions about its general validity. There is now a need for alternative theories of metabolic scaling that are consistent with empirical observations over a broad range of biological applications. In this article, we briefly review the limitations of FNT, examine the evidence that the two-variable power-law assumption is invalid, and outline alternative perspectives. In particular, we discuss quantum metabolism (QM), an analytic theory based on molecular-cellular processes. QM predicts the large variations in scaling exponent that are found empirically and also predicts the temperature dependence of the proportionality constant, issues that have eluded models such as FNT that are based on macroscopic and network properties of organisms.
Article
Metabolic energy fuels all biological processes, and therefore theories that explain the scaling of metabolic rate with body mass potentially have great predictive power in ecology. A new model, that could improve this predictive power, postulates that the metabolic scaling exponent (b) varies between 2/3 and 1, and is inversely related to the elevation of the intraspecific scaling relationship (metabolic level, L), which in turn varies systematically among species in response to various ecological factors. We test these predictions by examining the effects of lifestyle, swimming mode and temperature on intraspecific scaling of resting metabolic rate among 89 species of teleost fish. As predicted, b decreased as L increased with temperature, and with shifts in lifestyle from bathyal and benthic to benthopelagic to pelagic. This effect of lifestyle on b may be related to varying amounts of energetically expensive tissues associated with different capacities for swimming during predator-prey interactions.
Article
Because aerobic metabolic rates decrease in hypoxia-sensitive cells under oxygen-limiting conditions, the demand for glucose or glycogen for anaerobic glycolysis may rise drastically as a means of making up for the energetic shortfall. However, ion and electrical potentials typically cannot be sustained because of energy insufficiency and high membrane permeabilities; therefore metabolic and membrane functions in effect become decoupled. In hypoxia-tolerant animals, these problems are resolved through a number of biochemical and physiological mechanisms; of these metabolic arrest and stabilized membrane functions are the most effective strategies for extending tolerance to hypoxia. Metabolic arrest is achieved by means of a reversed or negative Pasteur effect (reduced or unchanging glycolytic flux at reduced O2 availability); and coupling of metabolic and membrane function is achievable, in spite of the lower energy turnover rates, by maintaining membranes of low permeability (probably via reduced densities of ion-specific channels). The possibility of combining metabolic arrest with channel arrest has been recognized as an intervention strategy. To date, the success of this strategy has been minimal, mainly because depression of metabolism through cold is the usual arrest mechanism used, and hypothermia in itself perturbs controlled cell function in most endotherms.
Article
Astronotus ocellatus is one of the most hypoxia tolerant fish of the Amazon; adult animals can tolerate up to 6 h of anoxia at 28 degrees C. Changes in energy metabolism during growth have been reported in many fish species and may reflect the way organisms deal with environmental constraints. We have analyzed enzyme levels (lactate dehydrogenase, LDH: EC 1.1.1.27; and malate dehydrogenase, MDH: EC 1.1.1.37) in four different tissues (white muscle, heart, liver, and brain) from different-sized animals. Both enzymes correlate with body size, increasing the anaerobic potential positively with growth. To our knowledge, this is the first description of scaling effects on hypoxia tolerance and it is interesting to explore the fact that hypoxia survivorship increases due to combining effects of suppressing metabolic rates and increasing anaerobic power as fish grow.
Article
Most animals experience some degree of hypoxia and hypothermia during the course of their natural life history either as a consequence of ambient 'exposure' per se or through metabolic, respiratory and/or circulatory insufficiency. A prevailing experimental approach has been to probe tissues from natural models of hypoxia-tolerant and cold-tolerant vertebrates to look for common mechanisms of defence against O(2) lack and hypothermia. The ability to sustain vital cellular functions in severe cases of either condition varies widely amongst the vertebrates. Like humans, the vast majority of mammals are unable to survive prolonged periods of hypothermia or O(2) deprivation owing to irreversible membrane damage and loss of cellular ion homeostasis in vital organs such as the brain and heart. However, numerous hibernating endotherms, neonatal and diving mammals as well as many ectotherms can tolerate prolonged periods that would, in clinical terms, be called asphyxia or deep hypothermia. The key to their survival under such conditions lies in an inherent ability to downregulate their cellular metabolic rate to new hypometabolic steady states in a way that balances the ATP demand and ATP supply pathways.
Article
The power function of basal metabolic rate scaling is expressed as aM(b), where a corresponds to a scaling constant (intercept), M is body mass, and b is the scaling exponent. The 3/4 power law (the best-fit b value for mammals) was developed from Kleiber's original analysis and, since then, most workers have searched for a single cause to explain the observed allometry. Here we present a multiple-causes model of allometry, where the exponent b is the sum of the influences of multiple contributors to metabolism and control. The relative strength of each contributor, with its own characteristic exponent value, is determined by the control contribution. To illustrate its use, we apply this model to maximum versus basal metabolic rates to explain the differing scaling behaviour of these two biological states in mammals. The main difference in scaling is that, for the basal metabolic rate, the O(2) delivery steps contribute almost nothing to the global b scaling exponent, whereas for the maximum metabolic rate, the O(2) delivery steps significantly increase the global b value.
Article
Metabolic control analysis has revealed that flux through pathways is the consequence of system properties, i.e. shared control by multiple steps, as well as the kinetic effects of various pathways and processes over each other. This implies that the allometric scaling of flux rates must be understood in terms of properties that pertain to the regulation of flux rates. In contrast, proponents of models considering the scaling of branching or fractal-like systems suggest that supply rates determine metabolic rates. Therefore, the allometric scaling of supply alone provides a sufficient explanation for the allometric scaling of metabolism. Examination of empirical data from the literature of comparative physiology reveals that basal metabolic rates (BMR) are driven by rates of energy expenditure within internal organs and that the allometric scaling of BMR can be understood in terms of the scaling of the masses and metabolic rates of internal organs. Organ metabolic rates represent the sum of tissue metabolic rates while, within tissues, cellular metabolic rates are the outcome of shared regulation by multiple processes. Maximal metabolic rates (MMR, measured as maximum rates of O2 consumption, VO2max) during exercise also scale allometrically, are also subject to control by multiple processes, but are due mainly to O2 consumption by locomotory muscles. Thus, analyses of the scaling of MMR must consider the scaling of both muscle mass and muscle energy expenditure. Consistent with the principle of symmorphosis, allometry in capacities for supply (the outcome of physical design constraints) is observed to be roughly matched by allometry in capacities for demand (i.e. for energy expenditure). However, physiological rates most often fall far below maximum capacities and are subject to multi-step regulation. Thus, mechanistic explanations for the scaling of BMR and MMR must consider the manner in which capacities are matched and how rates are regulated at multiple levels of biological organization.
Article
Fish cover a large size range, from milligrams to tonnes, and many of them are regularly exposed to large variations in ambient oxygen levels. For more than half a century, there have been various, often divergent, claims regarding the effect of body size on hypoxia tolerance in fish. Here, we attempt to link old and new empirical data with the current understanding of the physiological mechanisms behind hypoxia tolerance. Three main conclusions are drawn: (1) body size per se has little or no impact on the ability to take up oxygen during hypoxic conditions, primarily because the respiratory surface area matches metabolic rate over a wide size range. If size-related differences are seen in the ability for oxygen uptake in a species, these are likely to reflect adaptation to different life-styles or habitat choice. (2) During severe hypoxia and anoxia, where fish have to rely on anaerobic ATP production (glycolysis) for survival, large individuals have a clear advantage over smaller ones, because small fish will run out of glycogen or reach lethal levels of anaerobic end-products (lactate and H(+)) much faster due to their higher mass-specific metabolic rate. (3) Those fish species that have evolved extreme adaptations to hypoxia, including haemoglobins with exceptionally high oxygen affinities and an alternative anaerobic end-product (ethanol), reveal that natural selection can be a much more powerful determinant of hypoxia tolerance than scaling of physiological functions.
  • R R Sokal
  • F J Rohlf
Sokal R.R. and F.J. Rohlf. 1995. Biometry. W. H. Freeman, New York.
Tasmanian whitebait-a multi-species fishery targeting migrating fishes
  • W Fulton
Fulton W. 2000. Tasmanian whitebait-a multi-species fishery targeting migrating fishes. Pp. 256-260 in D.A. Hancock, D.C. Smith, and J.D. Koehn, eds. Fish movement and migration. Australian Society for Fish Biology Workshop Proceedings, Bendigo, September 28-29, 1999. Australian Society for Fish Biology, Sydney.