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... Chub inhabiting oxygen poor upstream sampling area had ∼10 % lower FCI compared to chub from oxygen rich downstream sampling area (Table 2). Dissolved oxygen is a key factor affecting the growth, reproduction, and survival of fishes (Friesen et al. 2012). In hypoxic conditions, energy may be diverted away from expenditures of growth, development, and reproduction, resulting in significant fitness costs (Kramer 1987), which could explain FCI decrease. ...
... In our study, chub were sampled in the late summer, i.e., in the postspawning period, and GSI determined for females at two oxygen poor upstream sites was on average close to 3 %, whereas for males it was close to 1.5 %, as opposed to oxygen rich downstream area with GSI of both sexes below 0.7 %. Since hypoxia may specifically disrupt the conversion of testosterone to estradiol through aromatase activity, resulting in higher testosterone levels and higher testosterone/estradiol ratio (Shang 2006;Landry et al. 2007;Friesen et al. 2012), it could also cause longer gonad development rate and consequently result in asynchronous breeding seasons between hypoxic and normoxic populations (Friesen et al. 2012). Some authors even suggest that the problem of endocrine disruption caused by hypoxia could potentially be more serious than that caused by known anthropogenic chemicals (Goldberg 1995;Diaz 2001). ...
... In our study, chub were sampled in the late summer, i.e., in the postspawning period, and GSI determined for females at two oxygen poor upstream sites was on average close to 3 %, whereas for males it was close to 1.5 %, as opposed to oxygen rich downstream area with GSI of both sexes below 0.7 %. Since hypoxia may specifically disrupt the conversion of testosterone to estradiol through aromatase activity, resulting in higher testosterone levels and higher testosterone/estradiol ratio (Shang 2006;Landry et al. 2007;Friesen et al. 2012), it could also cause longer gonad development rate and consequently result in asynchronous breeding seasons between hypoxic and normoxic populations (Friesen et al. 2012). Some authors even suggest that the problem of endocrine disruption caused by hypoxia could potentially be more serious than that caused by known anthropogenic chemicals (Goldberg 1995;Diaz 2001). ...
Article
The assessment of general condition of fish in the moderately contaminated aquatic environment was performed on the European chub (Squalius cephalus) caught in September 2009 in the Sutla River in Croatia. Although increases of the contaminants in this river (trace and macro elements, bacteria), as well as physico-chemical changes (decreased oxygen saturation, increased conductivity), were still within the environmentally acceptable limits, their concurrent presence in the river water possibly could have induced stress in aquatic organisms. Several biometric parameters, metallothionein (MT), and total cytosolic protein concentrations in chub liver and gills were determined as indicators of chub condition. Microbiological and parasitological analyses were performed with the aim to evaluate chub predisposition for bacterial bioconcentration and parasitic infections. At upstream river sections with decreased oxygen saturation (∼50 %), decreased Fulton condition indices were observed (FCI: 0.94 g cm(-3)), whereas gonadosomatic (GSI: 2.4 %), hepatosomatic (HSI: 1.31 %), and gill indices (1.3 %) were increased compared to oxygen rich downstream river sections (dissolved oxygen ∼90 %; FCI: 1.02 g cm(-3); GSI: 0.6 %; HIS: ∼1.08 %; gill index: 1.0 %). Slight increase of MT concentrations in both organs at upstream (gills: 1.67 mg g(-1); liver: 1.63 mg g(-1)) compared to downstream sites (gills: 1.56 mg g(-1); liver: 1.23 mg g(-1)), could not be explained by induction caused by increased metal levels in the river water, but presumably by physiological changes caused by general stress due to low oxygen saturation. In addition, at the sampling site characterized by inorganic and fecal contamination, increased incidence of bacterial bioconcentration in internal organs (liver, spleen, kidney) was observed, as well as decrease of intestinal parasitic infections, which is a common finding for metal-contaminated waters. Based on our results, it could be concluded that even moderate contamination of river water by multiple contaminants could result in unfavourable living conditions and cause detectable stress for aquatic organisms.
... Furthermore, in many fish species, low DO levels result in changes to energy allocation, leading to endocrine dis-ruption and the impairment of male reproductive processes (Wu et al. 2003;Landry et al. 2007; Thomas et al. 2007;Fitzpatrick et al. 2009;Martinovic et al. 2009). These effects include changes in the concentration and ratios of sex steroid hormones (Landry et al. 2007;Friesen et al. 2012), and disruption in gonad formation, fertilization, and spawning behaviour (Wu et al. 2003;Thomas et al. 2007;Kolding et al. 2008; Thomas and Rahman 2012). ...
... If trade-offs exist between somatic growth and reproduction for this species, a reduction in the physiological condition of swamp fish should be accompanied by reduced development of reproductive tissue (gonad mass), as found in other fish (Wu et al. 2003;Landry et al. 2007;Reardon and Chapman 2009). In the dwarf Victoria mouthbrooder (Pseudocrenilabrus multicolor victoriae Seegers, 1990), an African cichlid that inhabits environments with divergent oxygen regimes as does B. neumayeri, hypoxia has significant effects on female reproductive potential (Friesen et al. 2012). During the reproductive season, the swamp environment has a significantly lower number of brooding female P. m. victoriae than normoxic environments; this reduction may be due to an increase in testosterone levels and testosterone to estradiol ratio, which will affect gonad maturation (Friesen et al. 2012). ...
... In the dwarf Victoria mouthbrooder (Pseudocrenilabrus multicolor victoriae Seegers, 1990), an African cichlid that inhabits environments with divergent oxygen regimes as does B. neumayeri, hypoxia has significant effects on female reproductive potential (Friesen et al. 2012). During the reproductive season, the swamp environment has a significantly lower number of brooding female P. m. victoriae than normoxic environments; this reduction may be due to an increase in testosterone levels and testosterone to estradiol ratio, which will affect gonad maturation (Friesen et al. 2012). Similarly, we found that male GSI was reduced in fish from hypoxic sites compared with fish from normoxic sites. ...
... Pseudocrenilabrus multicolor victoriae is a small African cichlid fish, found throughout the Lake Victoria basin of East Africa across habitats that encompass a broad thermal range from 18.1°C in the dense interior of papyrus swamps to 30.8°C (Chapman et al., 2002;Friesen et al., 2012) in warm ecotonal waters of lakes. This study measured the effect of temperature on aerobic performance in laboratory-acclimated stock P. multicolor. ...
... 31°52′ 0.00″E). Water temperature and dissolved oxygen (DO) at the Bwera site averages 21.7°C (range = 17.3 to 25.7°C) and 0.28 mg L −1 , respectively (Crispo and Chapman, 2010;Friesen et al., 2012); while at the Lake Kayanja ecotone, water temperature and DO are both higher, 25.3°C (range = 21.6 to 31.1°C) and 6.97 mg L − 1 , respectively (McDonnell and Chapman, 2015). P. multicolor were live-transferred to McGill University in either July 2011 (Bwera) or July 2013 (Kayanja). ...
Article
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Rising water temperature associated with climate change is increasingly recognized as a potential stressor for aquatic organisms, particularly for tropical ectotherms that are predicted to have narrow thermal windows relative to temperate ectotherms. We used intermittent flow resting and swimming respirometry to test for effects of temperature increase on aerobic capacity and swim performance in the widespread African cichlid Pseudocrenilabrus multicolor victoriae, acclimated for a week to a range of temperatures (2 °C increments) between 24 and 34 °C. Standard metabolic rate (SMR) increased between 24 and 32 °C, but fell sharply at 34 °C, suggesting either an acclimatory reorganization of metabolism or metabolic rate depression. Maximum metabolic rate (MMR) was elevated at 28 and 30 °C relative to 24 °C. Aerobic scope (AS) increased between 24 and 28 °C, then declined to a level comparable to 24 °C, but increased dramatically 34 °C, the latter driven by the drop in SMR in the warmest treatment. Critical swim speed (Ucrit) was highest at intermediate temperature treatments, and was positively related to AS between 24 and 32 °C; however, at 34 °C, the increase in AS did not correspond to an increase in Ucrit, suggesting a performance cost at the highest temperature.
... gill and brain size, metabolic rate, egg size) persists despite high gene flow between habitats divergent in DO (Crispo & Chapman, 2008. Pseudocrenilabrus multicolor from low-DO habitats also have higher than normal testosterone : oestradiol ratios, which is considered to be induced by impaired enzyme function under low oxygen (Friesen, Aubin-Horth & Chapman, 2012). Such disruptions could lead to reproductive impairments by altering behaviour and gonad maturation. ...
... Pseudocrenilabrus multicolor were collected from paired sites from two drainages in Uganda, East Africa (see Supporting information, Fig. S1, Table S1): the Lake Nabugabo region that lies in the Lake Victoria basin and the Mpanga River drainage of western Uganda. These well-characterized paired sites (Crispo & Chapman, 2008;Friesen et al., 2012;Crocker et al., 2013) represent extremes of DO content. Swamps have a naturally low DO as a result of excess organic matter, whereas rivers tend to be more oxygenated; thus, the swamps represent naturally hypoxic sites where fish have likely persisted for many generations. ...
Article
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Species that cross strong environmental gradients are expected to face divergent selective pressures that can act on sexually-selected traits. In the present study, we examine the role of hypoxia and carotenoid availability in driving divergence in two sexually-selected traits, male colour and reproductive behaviour, in the African cichlid Pseudocrenilabrus multicolor victoriae. Low-dissolved oxygen (DO) (hypoxic) environments are expected to be energetically challenging; given that male nuptial colour expression and courtship displays can be costly, we expected fish in low-DO versus high-DO environments to differ in these traits. First, a field survey was used to describe natural variation in male nuptial colour patterns and diet across habitats divergent in DO. Next, using wild-caught fish from a low-DO and high-DO habitat, we tested for differences in reproductive behaviour. Finally, a laboratory rearing experiment was used to quantify the interaction of DO and diet (low- versus high-carotenoid availability) on the expression of male colour during development. In energetically challenging low-DO environments, fish were more red and, in high-DO environments, fish were typically brighter and more yellow. The frequency of reproductive displays in fish of low-DO origin was 75% lower, although this had no consequence for brooding frequency (i.e. both populations produced the same number of broods on average). Our laboratory rearing study showed carotenoid availability to be important in colour production with no direct influence of DO on colour. Additionally, weak patterns of diet variation across wild populations suggest that other factors in combination with diet are contributing to colour divergence.
... Furthermore, in many fish species, low DO levels result in changes to energy allocation, leading to endocrine disruption and the impairment of male reproductive processes (Wu et al. 2003; Landry et al. 2007; Thomas et al. 2007; Fitzpatrick et al. 2009; Martinovic et al. 2009). These effects include changes in the concentration and ratios of sex steroid hormones (Landry et al. 2007; Friesen et al. 2012), and disruption in gonad formation, fertilization , and spawning behaviour (Wu et al. 2003; Thomas et al. 2007; Kolding et al. 2008; Thomas and Rahman 2012). ...
Article
In this study, we explored variation in sperm morphometry of the African cyprinid Barbus neumayeri Fischer, 1884 (Neumayer's barb) across seven sites with a wide range in dissolved oxygen, from hypoxic swamps to intermittent normoxic streams to well-oxygenated rivers. We explore whether fish physiological condition (K) or hypoxia can affect the reproductive traits, and whether condition-hypoxia dependence of sperm traits including head length (L-H), head width (W-H), flagellum length (L-F), and hydrodynamic ratio (HR) vary across sampling sites. Significant differences were found in fish total length (P = 0.0212), as well as in K, left and right testis masses, total gonad mass, and gonadosomatic index (P < 0.0001 for all traits). Total gonad mass was lower in hypoxic sites than in well-oxygenated sites. Interestingly, the left and right testes from normoxic environments were double the size of testes from hypoxic environments. Despite little variation in sperm flagellum length, sperm heads were longer in swamps than in streams or rivers, giving the sperm head a more hydrodynamic shape. This variation in HR may be beneficial in the more stagnant waters of the swamp compared with the other environments. Future studies are necessary to understand whether variation in sperm morphology correlates with sperm swimming performance and male reproductive capacity.
... Further, the gonadal recrudescence in male croakers was significantly impaired during hypoxia, as evidenced by an apparent decline in spermatogenesis and the production of mature sperm, which was associated with decreased 11-KT signaling for regulating gametogenesis. A field survey made by Friesen et al. (2012), clearly indicated that geographical separation plays a critical role in sustaining estradiol in female African cichlid (Pseudocrenilabrus multicolor victoriae). They further suggested that hypoxia can also affect the levels of T, the T/E2 ratio, and the percentage of brooders in the female African cichlid. ...
Article
Vast stretches of open water bodies are gradually becoming hypoxic as a result of depletion of oxygen levels mainly due to various human anthropogenic activities. This problem of hypoxic stress on the fish population is likely to be exacerbated soon since the aquatic hypoxic environment is continuously spreading over vast areas worldwide. In recent years, various harmful effects of hypoxia to bony fishes have been reported, such as the restriction of energy-consuming metabolic processes, arrest of the growth of ovary and testes that are associated with endocrine disruption, loss of sperm and egg quality, inhibition of fertilization, hatching success, and also the reduction of larval survivability, thereby impairment of overall reproductive and developmental processes in fish. Disruption of the brain-pituitary-gonad axis, and certain enzymes related to steroidogenesis and vitellogenesis in fish have also been reported as the primary targets for an endocrine malfunction during hypoxia. Hypoxia-sensitive downregulation of key genes responsible for controlling sex hormones' synthesis has been documented in certain bony fishes. Further, continuous exposure to hypoxia was reported to induce early expression of pro-apoptotic/tumor suppressor p53 genes, thereby causing immense cell death in hypoxic embryos. However, the cellular responses to long-term hypoxia exposure and the degree of reproductive impairments in bony fishes are still not adequate to figure out the actual underlying mechanisms. The present review intends to highlight the current knowledge about the detrimental impact of chronic/acute hypoxia at different stages of fish reproduction and the associated underlying molecular mechanisms.
... This species is a maternal mouthbrooder, with the eggs and developing young held in the female's mouth for 13-21 days (Reardon and Chapman, 2010b). Across habitats in Uganda, P. multicolor persists under a broad thermal range from 18.1°C in the dense interior of papyrus swamps to 30.8°C in warm ecotonal waters of lake systems (Chapman et al., 2002;Friesen et al., 2012). Thus, this species provides a useful model both for understanding the mechanisms underlying broad thermal distributions and for testing specific predictions related to thermal capacity in tropical ectotherms. ...
Article
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Tropical inland fishes are predicted to be especially vulnerable to thermal stress because they experience small temperature fluctuations that may select for narrow thermal windows. In this study, we measured resting metabolic rate (RMR), critical oxygen tension (Pcrit) and critical thermal maximum (CTMax) of the widespread African cichlid (Pseudocrenilabrus multicolor victoriae) in response to short-term acclimation to temperatures within and above their natural thermal range. Pseudocrenilabrus multicolor collected in Lake Kayanja, Uganda, a population living near the upper thermal range of the species, were acclimated to 23, 26, 29 and 32°C for 3 days directly after capture, and RMR and Pcrit were then quantified. In a second group of P. multicolor from the same population, CTMax and the thermal onset of agitation were determined for fish acclimated to 26, 29 and 32°C for 7 days. Both RMR and Pcrit were significantly higher in fish acclimated to 32°C, indicating decreased tolerance to hypoxia and increased metabolic requirements at temperatures only slightly (∼1°C) above their natural thermal range. The CTMax increased with acclimation temperature, indicating some degree of thermal compensation induced by short-term exposure to higher temperatures. However, agitation temperature (likely to represent an avoidance response to increased temperature during CTMax trials) showed no increase with acclimation temperature. Overall, the results of this study demonstrate that P. multicolor is able to maintain its RMR and Pcrit across the range of temperatures characteristic of its natural habitat, but incurs a higher cost of resting metabolism and reduced hypoxia tolerance at temperatures slightly above its present range.
... rts this hypothesis ( Breit - burg et al . , 2009 ; Pollock et al . , 2010 ; Thomas and Rahman , 2012 ; Wu et al . , 2003 ) . In the African cichlid Egyptian mouth - brooder , Pseudocrenilabrus multicolor victoriae , for example , it was reported that fish exposed to hypoxic conditions exhibited higher levels of T than normally - oxygenated fish ( Friesen et al . , 2012 ) ; although the E 2 levels were not affected , the sex hormone balance favored T . Baroiller and co - authors had previously hypothesized that , as in mammals , hypoxia can induce apoptosis of the primordial germ cells ( PGCs ) in zebrafish ( Baroiller et al . , 2009 ) , and it is known that PGCs depletion is related to testicular diff ...
... In our study, this could explain the greater stress sensitivity of male as compared to females that were not significantly affected by co-exposure of hypoxia and acidification. In fish studies, abundant evidence showed that hypoxia is related to endocrine disruption (Landry et al., 2007;Friesen et al., 2012;Halem et al., 2014). Hypoxia could mediate inhibition of cytochrome P450 aromatase (an enzyme responsible for estrogens biosynthesis) activity (Halem et al., 2014), such mechanism may impact the sexual differentiation of fish (Landry et al., 2007), but further research is needed for mussels. ...
Article
Ocean acidification and hypoxia have become increasingly severe in coastal areas, and their co-occurrence poses emerging threats to coastal ecosystems. Here, we investigated the combined effects of ocean acidification and hypoxia on the reproductive capacity of the thick-shelled mussel Mytilus coruscus. Our results demonstrated low pH but not low oxygen induced decreased gonadosomatic index (GSI) in mussels. Male mussels had a lower level of sex steroids (estradiol, testosterone, and progesterone) when kept at low pH. Expression of genes related to reproduction were also impacted by low pH with a downregulation of genes involved in gonad development in males (β-catenin and Wnt-7b involved in males) and an upregulation of testosterone synthesis inhibition-related gene (Wnt-4) in females. Overall, our results suggest that ocean acidification has an impact on the gonadal development through an alternation of gene expression and level of steroids while hypoxia had no significant effect.
... Our findings concur with Friesen et al. (2012) and other recent studies that correlate low dissolved oxygen with endocrine disruption in fish species (Wu et al., 2003;Landry et al., 2007). The pathway for such an alteration was identified as a hypoxia mediated inhibition of cytochrome P450 aromatase activity (Alzieu, 2000;Matthiessen and Gibbs, 1998;Morcillo and Porte, 2000;Shang et al., 2006). ...
Article
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Populations undergo physiological adaptations in response to environmental stressors. Our five-year bio-monitoring study of the Bronx River Estuary demonstrates comparatively low dissolved oxygen concentrations in this urbanized watershed. Additionally, our current results establish altered hormonal levels, resulting from endocrine disruption, in Geukensia demissa (Atlantic ribbed mussel) from the Bronx River Estuary. No studies have yet investigated a correlation between low dissolved oxygen and endocrine disruption in field-collected bivalves. Testosterone, estradiol, and progesterone levels were collected from male and female mussels in the oxygen depleted Bronx River and well-oxygenated Greenwich Cove. Bronx River mussels exhibited higher testosterone levels and lower estradiol levels than Greenwich Cove mussels. The resulting abnormal hormonal ratio seems to indicate that environmental conditions in the Bronx River facilitate an allosteric inhibition of the cytochrome P450 aromatase enzyme, which aids conversion of testosterone to estradiol. Low progesterone levels suggest Bronx River mussels are experiencing a delay in sexual maturation, and morphometric data show a stalling of shell and tissue growth. To confirm that the mussels collected from both sites are the same species, the universal mitochondrial cytochrome c oxidase subunit I gene was analyzed, through DNA barcoding. Minimal sequential heterogeneity confirmed the mussels are the same species. Such findings suggest intraspecific divergence in various endocrine processes, resulting from environmentally induced stress.
... These environmental factors may include temperature (Brown, Baumann, & Conover, 2014;Ospina-Alvarez & Piferrer, 2008;Pandian, 2015), stocking density (Çek et al., 1998;Ribas, Valdivieso, Díaz, & Piferrer, 2017;Saillant et al., 2003), salinity (Abucay, Mair, Skibinski, & Beardmore, 1999), hypoxia (Cheung, Chiu, & Wu, 2014;Friesen, Aubin-Horth, & Chapman, 2012;Shang, Yu, & Wu, 2006), and other environmental stressors (Brown et al., 2014;Mankiewicz et al., 2013) that are known to stimulate the hypothalamus-pituitary-interrenal axis and in some cases manifest in sex reversal. In addition, future research avenues should focus on the use of exogenous hormones such as MT, which has been shown to be efficacious in masculinizing over 25 species (Pandian, 2015;Pandian & Sheela, 1995). ...
Article
Sexual differentiation in teleosts is based on diverse and complex combinations of genetic and environmental factors. Environmental conditions during early development can alter gonadal differentiation leading to sex reversal, where the individual's genotypic and phenotypic sexes are opposite. In many species, the mechanism of environmental sex reversal has been linked to the stress axis and fluctuations in cortisol. This mechanism could be utilized to manipulate sex ratios in ornamental aquaculture, where the males of sexually dichromic species are often more economically valuable due to their brighter coloration. Dietary cortisol administration was used as a proxy for environmental stress to evaluate the effects on gonadal differentiation in two ornamental species, rosy barb, Pethia conchonius and dwarf gourami, Trichogaster lalius . Three experiments were run with each species to assess the following: (a) postprandial cortisol levels following dietary administration, (b) the effect of dietary cortisol concentration on sex ratios, and (c) the effect of developmental timing of cortisol feed administration on sex ratios. Whole‐body cortisol enzyme‐linked immunosorbent assays confirmed that cortisol feed did cause increased cortisol levels. However, despite cortisol feed being administered during the putative gonadal differentiation period, no effect was observed in the final sex ratios for any of the treatments evaluated.
... However, M. nipponense exhibits higher oxygen consumption and asphyxia point than other crustacean species (Sun et al., 2014), and the hypoxia-sensitive characteristics of M. nipponense present problems for large-scale aquaculture. In aquaculture ponds, the dissolved oxygen (DO) concentration frequently decreases to less than 2.8 mg/L, resulting in hypoxia (Friesen et al., 2012) and major economic losses (Wu et al., 2003). Thus, the regulation mechanism of hypoxia in M. nipponense needs to be researched. ...
... The reported sublethal effects of hypoxia on fish reproduction include changes in reproductive or brood-caring behaviour (Courtenay and Keenleyside 1983;Jones and Reynolds 1999a, 1999b, 1999cWang et al. 2008), hormonal disturbances (Dabrowski et al. 2003;Wu et al. 2003;Friesen et al. 2012), reductions in the size of the testes and ovaries (Landry et al. 2007;Cheek et al. 2009) reduced sperm production and motility (Wu et al. 2003;Thomas and Rahman 2010), reduced spawning success (Wu et al. 2003), decreased brood size and egg viability (Wu et al. 2003;Thomas et al. 2006;Landry et al. 2007), diminished larval survival following parental exposure (Wu et al. 2003) and transgenerational effects on some species, which may be negative (Wang et al. 2016) or positive by increasing the resistance of larvae to hypoxia (Ho and Burggren 2012). Sublethal exposure of eggs or larvae to hypoxia can also be detrimental. ...
Article
Hypoxia can profoundly affect fish reproduction and larval development, but its effects on fish from tropical Australia are not well understood. In the present study, the effects of diel fluctuating hypoxia on reproduction and embryo viability were investigated for a range-limited tropical freshwater fish, namely the Utchee Creek rainbowfish (Melanotaenia utcheensis). The lethal level for adult rainbowfish after gradual oxygen depletion was ∼7% dissolved oxygen (DO) saturation. After 28 days, the reproductive success of adult fish exposed to fluctuating hypoxia treatments was measured by fecundity, gonad health, egg incubation time, egg and larval mortality, viability and size of hatching larvae. Reproduction was impaired in the lowest sublethal treatment (minimum 10% DO saturation each day). No ill effects of parental exposure to diel fluctuating hypoxia on embryos were identified, and minor differences in temperature between aquaria had a greater effect on embryos than parental hypoxia treatments. Similarly, no effects of embryonic exposure to diel fluctuating hypoxia were identified. Utchee Creek rainbowfish appear to be more hypoxia tolerant than temperate species, in keeping with their habitat in warm lowland streams, but they are still susceptible to the increasing frequency and intensity of hypoxia possible with increasing temperature and reduced flow as a result of climate change.
... Both type of air bubbling, i.e., oxygen and nitrogen flow were provided into each aquarium tank. The oxygen and nitrogen bubbling was adjusted with the regulator to obtain the desired level (Friesen et al., 2012). Within four hours, the DO level was reduced to the hypoxia level and maintained at 0.5 ± 0.16 mg l −1 DO for 15 days. ...
Article
Vitamin E is of importance for several physiological processes, some of which also apply to fish. Here, we conducted an experiment to assess the effect of environmental hypoxia and dietary vitamin E on oxidative status and tissue injury in a bottom dwelling carp, Cirrhinus mrigala (Ham., 1822). The four treatments combined oxygen availability (Normoxia/Hypoxua) and Vitamin E presence/absence. Lipid peroxidation parameters such as thiobarbituric acid reactive substances (TBAR), peroxide value (PV), polyunsaturated fatty acids/saturated fatty acid (PUFA/SFA) ratio, catalase (CAT), superoxide dismutase (SOD) and erythrocyte fragility were assessed. The results indicate that exposure to hypoxia elevates these parameters. However, the supplementation of vitamin E via the diet effectively reduced erythrocyte membrane damage (EF) and myeloperoxidase activity (MPO), which were enhanced by the exposure to hypoxia. Dietary vitamin E also improved antioxidant enzyme status in the hypoxia exposed fish, as indicated by the decreased catalase and superoxide dismutase activities. Vitamin E supplementation also compensated for increased levels of peroxide value, thiobarbituric acid reactive substances, and an increased polyunsaturated fatty acids/saturated fatty acid ratio resulting from the exposure to hypoxia. Overall, it can be concluded that fortification of vitamin E in the diet of this carp species, and possibly other fish that live under hypoxic conditions, can restore the antioxidant status and well-being to some extent.
... Further, the gonadal recrudescence in male croakers was significantly impaired during hypoxia, as evidenced by an apparent decline in spermatogenesis and the production of mature sperm, which was associated with decreased 11-KT signaling for regulating gametogenesis. A field survey made by Friesen et al. (2012), clearly indicated that geographical separation plays a critical role in sustaining estradiol in female African cichlid (Pseudocrenilabrus multicolor victoriae). They further suggested that hypoxia can also affect the levels of T, the T/E2 ratio, and the percentage of brooders in the female African cichlid. ...
Article
Full-text available
Vast stretches of open water bodies are gradually becoming hypoxic as a result of depletion of oxygen levels mainly due to various human anthropogenic activities. This problem of hypoxic stress on the fish population is likely to be exacerbated soon since the aquatic hypoxic environment is continuously spreading over vast areas worldwide. In recent years, various harmful effects of hypoxia to bony fishes have been reported, such as the restriction of energy-consuming metabolic processes, arrest of the growth of ovary and testes that are associated with endocrine disruption, loss of sperm and egg quality, inhibition of fertilization, hatching success, and also the reduction of larval survivability, thereby impairment of overall reproductive and developmental processes in fish. Disruption of the brain-pituitary-gonad axis, and certain enzymes related to steroidogenesis and vitellogenesis in fish have also been reported as the primary targets for an endocrine malfunction during hypoxia. Hypoxia-sensitive downregulation of key genes responsible for controlling sex hormones' synthesis has been documented in certain bony fishes. Further, continuous exposure to hypoxia was reported to induce early expression of pro-apoptotic/tumor suppressor p53 genes, thereby causing immense cell death in hypoxic embryos. However, the cellular responses to long-term hypoxia exposure and the degree of reproductive impairments in bony fishes are still not adequate to figure out the actual underlying mechanisms. The present review intends to highlight the current knowledge about the detrimental impact of chronic/acute hypoxia at different stages of fish reproduction and the associated underlying molecular mechanisms.
Article
Sex reversal is one of the characteristic properties of sexual plasticity in bony fishes wherein both natural and induced sex change happens at various stages of life cycle in different species. Sex determination in gonochoristic species is genetically regulated, wherein the same sex is retained throughout their life span whereas hermaphrodites change their sex during development or adulthood. In sequential hermaphrodites, serial sex change occurs at different points of life cycle. Concurrently, synchronous hermaphrodites function as both the sexes during spawning. Other variables like temperature, pH and social factors can trigger sex reversal in teleost. Sex reversal through gene mutations and chemicals/hormones, including sex steroids, can be induced mostly at early developmental stages but natural sex reversal can occur at any time. Sex reversal mechanism shows morphological to molecular changes, which are ideal for identification of sex-specific gene markers. In fact, gonadal transdifferentiation occurs at the molecular level through differential expression of transcription factors and steroidogenic enzyme genes vis-a-vis hormones, thereby imparting phenotypic or structural changes. In addition, brain shows sexual dimorphism which is mostly consequential to gonadal sex development and occasionally either causative. The major breakthrough in this line is the identification of sex determining genes such as dmy/dmrt1Yb, gsdfY, sox3 in the Japanese medaka and amhY in Patagonian pejerrey. Incidentally, the induction of mono-sex population by favouring one sex due to sex-specific differences in growth is an important economic boom for aquaculture. This review comprehensively highlights key molecular factors involved in natural and induced sex reversal conditions to illustrate teleostean sexual plasticity and its application perspectives.
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Besides the well-known function of thyroid hormones (THs) for regulating metabolism, it has recently been discovered that THs are also involved in testicular development in mammalian and non-mammalian species. THs, in combination with follicle stimulating hormone, lead to androgen synthesis in Danio rerio, which results in the onset of spermatogenesis in the testis, potentially relating the hypothalamic-pituitary-thyroid (HPT) gland to the hypothalamic-pituitary-gonadal (HPG) axes. Furthermore, studies in non-mammalian species have suggested that by stimulating the thyroid-stimulating hormone (TSH), THs can be induced by corticotropin-releasing hormone. This suggests that the hypothalamic-pituitary-adrenal/interrenal gland (HPA) axis might influence the HPT axis. Additionally, it was shown that hormones pertaining to both HPT and HPA could also influence the HPG endocrine axis. For example, high levels of androgens were observed in the testis in Odonthestes bonariensis during a period of stress-induced sex-determination, which suggests that stress hormones influence the gonadal fate toward masculinization. Thus, this review highlights the hormonal interactions observed between the HPT, HPA, and HPG axes using a comparative approach in order to better understand how these endocrine systems could interact with each other to influence the development of testes.
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Aquatic hypoxia is generally viewed as stressful for aerobic organisms. However, hypoxia may also benefit organisms by decreasing cellular stress, particularly that related to free radicals. Thus, an ideal habitat may have the minimum O2 necessary to both sustain aerobic metabolism and reduce the need to scavenge free radicals and repair free radical damage. The ability of aquatic organisms to sustain aerobic metabolism relates in part to the ability to maximize gas diffusion, which can be facilitated by small body size when O2 uptake occurs across the body surface, by a large gill surface area, or by the ability to use atmospheric air. We use water-breathing organisms in chronically hypoxic papyrus (Cyperus papyrus) swamps of East Africa to test the hypothesis that cellular-level benefits of hypoxia may translate into increased fitness, especially for small organisms. A review of recent studies of fingernail clams (Sphaerium sp.) shows that clams living in sustained hypoxia have minimized oxidative stress and that these cellular-level benefits may lead to increased fitness. We suggest that organisms in the extreme conditions in the papyrus swamps provide a unique opportunity to challenge the conventional classification of hypoxic habitats as 'stressful' and normoxic habitats as 'optimal.'
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In recent years, natural and anthropogenic factors have increased aquatic hypoxia the world over. In most organisms, the cellular response to hypoxia is mediated by the master regulator hypoxia-inducible factor-1 (HIF-1). HIF-1 also plays a critical role in the normal development of the cardiovascular system of vertebrates. We tested the hypothesis that hypoxia exposures which resulted in HIF-1 induction during embryogenesis would be associated with enhanced hypoxia tolerance in subsequent developmental stages. We exposed zebrafish (Danio rerio) embryos to just 4 h of severe hypoxia or total anoxia at 18, 24 and 36 h post-fertilization (hpf). Of these, exposure to hypoxia at 24 and 36 hpf as well as anoxia at 36 hpf activated the HIF-1 cellular pathway. Zebrafish embryos that acutely upregulated the HIF-1 pathway had an increased hypoxia tolerance as larvae. The critical window for hypoxia sensitivity and HIF-1 signalling was 24 hpf. Adult male fish had a lower critical oxygen tension (Pcrit) compared with females. Early induction of HIF-1 correlated directly with an increased proportion of males in the population. We conclude that mounting a HIF-1 response during embryogenesis is associated with long-term impacts on the phenotype of later stages which could influence both individual hypoxia tolerance and population dynamics.
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As the end of the continuous event, environmental sex determination (ESD) is considered as a counterpart of genotypic sex determination (GSD), with GSD plus environmental effects (GSD + EE) as the transition between them. The downstream pathway is somewhat conserved between GSD and ESD, though they are essentially different in terms of how sex is determined. The direct target(s) of environmental factors involved in ESD in fish have not yet been characterized. Since there is very little genetic difference between sexes in ESD, we propose two pathways here – namely, epigenetics and hormone‐gene‐cell interactions – to deduce how sex is determined in ESD and, specifically, how environmental signals are transduced into target organs and decide the fate of sex. For the first time, we propose that for ESD species, environmental factors transduce signals via stress response pathway. Sex is then determined via the interactions of hormones, genes, and cells, which are modulated by cortisol, the main stress hormone in fish. Recent advancement strongly suggests that sex differentiation involves a bewildering network of multi‐level, multi‐gene, multi‐hormone, multi‐target interactions on undifferentiated and differentiating gonads, and the realization of ovarian or testicular development is the results of the two antagonistic roles of male‐specific genes and female‐specific genes. Lastly, we also discuss how we can make best use of ESD, and how we can avoid the negative influence in aquaculture and fisheries.
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Hypoxia is amongst the most widespread and pressing problems in aquatic environments. Here we demonstrate that fish (Oryzias melastigma) exposed to hypoxia show reproductive impairments (retarded gonad development, decrease in sperm count and sperm motility) in F1 and F2 generations despite these progenies (and their germ cells) having never been exposed to hypoxia. We further show that the observed transgenerational reproductive impairments are associated with a differential methylation pattern of specific genes in sperm of both F0 and F2 coupled with relevant transcriptomic and proteomic alterations, which may impair spermatogenesis. The discovered transgenerational and epigenetic effects suggest that hypoxia might pose a dramatic and long-lasting threat to the sustainability of fish populations. Because the genes regulating spermatogenesis and epigenetic modifications are highly conserved among vertebrates, these results may also shed light on the potential transgenerational effects of hypoxia on other vertebrates, including humans.
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The co-occurrence of hypoxia and xenobiotics is extremely common in natural environments, highlighting the necessity to elicit their interaction on aquatic toxicities. In the present study, marine medaka embryos were exposed to various concentrations (nominal 0, 1, 3.3 and 10 mg/L) of perfluorobutane sulfonate (PFBS), an environmental pollutant of emerging concern, under either normoxia (6.9 mg/L) or hypoxia (1.7 mg/L) condition. After acute exposure till 15 days post-fertilization, single or combined toxicities of PFBS and hypoxia on embryonic development (e.g., mortality, hatching and heartbeat) and endocrine systems were investigated. Sex and thyroid hormones were measured by enzyme-linked immunosorbent assay. Transcriptional changes of endocrine genes were determined by quantitative real-time PCR assays. Co-exposure to 10 mg/L PFBS and hypoxia caused a further reduction in survival rate and heart beat compared to single exposure. PFBS induced a precocious hatching, while no larvae hatched under hypoxia condition. By disturbing the balance of sex hormones, either PFBS or hypoxia single exposure produced an anti-estrogenic activity in medaka larvae. However, PFBS and hypoxia combinations reversed to estrogenic activity in co-exposed larvae. Variation in disrupting pattern may be attributed to the interactive effects on steroidogenic pathway involving diverse cytochrome P450 enzymes. Regarding thyroid system, PFBS exposure caused detriments of multiple processes along thyroidal axis (e.g., feedback regulation, synthesis and transport of thyroid hormones, receptor-mediated signaling and thyroid gland development), while hypoxia potently impaired the development and function of thyroid gland. Combinations of PFBS and hypoxia interacted to dysregulate the function of thyroid endocrine system. In summary, the present study revealed the dynamic interaction of PFBS pollutant and hypoxia on aquatic developmental toxicities and endocrine disruption. Considering the frequent co-occurrence of xenobiotics and hypoxia, current results would be beneficial to improve our understanding about their interactive mechanisms and provide baseline evidences for accurate ecological risk evaluation.
Article
Perfluorobutane sulfonate (PFBS), an environmental pollutant of emerging concern, is previously shown to dynamically interact with hypoxia on aquatic developmental toxicities. However, the molecular mechanisms underlying the interaction remain unknown. In this follow-up study, marine medaka embryos were exposed to 0 and 3.3 mg/L of PFBS under normoxia (6.9 mg/L) or hypoxia (1.7 mg/L) condition till 15 days post-fertilization. High-throughput transcriptomic sequencing was employed to filter differentially expressed genes and provide mechanistic insight into interactive action between hypoxia and PFBS. The results showed that hypoxia alone and the coexposure paradigm were similarly potent to modify transcriptional profiles, with the majority of genes significantly down-regulated. In contrast, transcriptional toxicity of PFBS was relatively milder. Functional annotation analyses found that hypoxia and coexposure groups mainly impacted phototransduction signaling by decreasing the transcriptions of cyclic nucleotide-gated (CNG) cation channels and retinol transport genes. However, this study demonstrated the first toxicological evidence that toxic effects of PFBS targeted the perception of chemical stimulus through olfactory and gustatory receptors. The addition of PFBS moderately exacerbated the toxic actions of hypoxia, which largely shaped the transcriptional pattern of coexposure group. In addition, gene interactive networks were constructed for hypoxia and coexposure groups, underlining the increased chromatin deacetylation and methylation to epigenetically repress genome-wide transcriptional initiation. Overall, PFBS and hypoxia interact to interrupt the embryonic development of sensory systems, which may compromise the individual fitness and survival, especially during early life stages when precocious perception of food and escape from predators are essential.
Chapter
Cichlid fishes are champion caregivers that protect, clean, aerate, and sometimes even feed their young. This tropical fish family’s extensive species radiation combined with great diversity in care habits make cichlids immensely useful models for studying the evolution of parental care. In this chapter, we review the diverse ways that care is provided (~1/3 of species guard young on the ground and 2/3 mouthbrood) and the variation in sex of the caregiver (42% of species have biparental care, 58% show the derived state of female-only care). Substrate guarding, the ancestral form of care, is especially common among New World cichlids. In contrast, mouthbrooding, dominates in African clades. We also describe two forms of expanded (allo) care: (1) brood mixing where parents care for non-descendant young; and (2) cooperative breeding with joint care by an entire social group. Such cooperative breeding, arguably one of the most socially complex breeding systems, has arisen at least 5X among cichlids, all within a single clade, the Lamprologines of Lake Tanganyika. Using one well-studied cooperative species, Neolamprologus pulcher, as an example, we review the various possible explanations for the evolution of cooperative care. We conclude by discussing some exciting future directions for the study of parental care in cichlids.
Chapter
For fishes, the availability of dissolved oxygen (DO) can affect performance and fitness traits and influence distribution patterns. Hypoxia occurs naturally in habitats characterized by low mixing and/or light limitation such as dense wetlands and profundal zones of deep lakes. In addition, human activities are increasing the frequency and extent of aquatic hypoxia through eutrophication and pollution. Thus, it has become increasingly important to understand consequences of hypoxia for fishes and mechanisms that facilitate persistence in low-DO habitats. With strong specialization in some cichlid species and high levels of intraspecific variation in others, cichlids have been a key group for exploring strategies for dealing with hypoxia. These include behavioral responses (e.g. aquatic surface respiration), evolution of mechanisms to maximize oxygen uptake and delivery, metabolic depression, use of anaerobic metabolism, and air breathing in a few species. Despite the diversity of strategies that have permitted some cichlids to persist under extreme hypoxia, low DO can incur potential costs such as smaller body size. Such costs may be offset by benefits of hypoxic habitats such as reduced predation risk. This review details the mechanisms used by cichlids for tolerating hypoxia and the costs and benefits of hypoxia tolerance.
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Very little work has determined the relative importance of uncontrolled environmental factors for affecting fish biology, and how these might influence gillnet catches. This study addresses this deficit for an important Southeast Asian cyprinid (Barbonymus schwanenfeldii). Fish were caught monthly for 12 months using gillnets of three different mesh sizes, each of which was deployed in duplicate at the surface of one of three randomly selected sites in Lake Kenyir, Malaysia, concurrent with determining various environmental parameters and the abundance of phytoplankton (chlorophyll–a). Results indicated that growth co-efficient of B. schwanenfeldii was positively influenced by dissolved oxygen and negatively influenced by total inorganic nitrogen, whereas an opposite result was observed in case of the hepatosomatic index of fish. Water turbidity was a limiting factor only for small fish (mean total length: 15.74±1.10 cm). B. schwanenfeldii could best be caught during the period of high phytoplankton abundance or at the location of high phytoplankton density in the water. Water temperature negatively influenced the gillnet catches of the fish. The remaining environmental factors such as water depth, pH, and phosphate had a weak and insignificant influence (P >0.05) on the biology and gillnet catches of fish. The observed results can be very useful for the ecological monitoring and conservation plans for this species in relation to climate change. Furthermore, the utility of the similar data for other species would be useful not only for regional but also for international fishery by optimizing catches considering environmental conditions.
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Growth, size at maturity, gonadosomatic index (GSI), egg size, and absolute fecundity of Nile tilapia (Oreochromis niloticus) were significantly affected by oxygen levels (1.5 +/- 1.0, 2.8 +/- 1.4, and 6.0 +/- 1.8 mg center dot L-1) in a controlled experiment designed to test the hypothesis (D. Pauly. 1984. J. Cons. Int. Explor. Mer, 41: 280-284) that O-2 is the controlling factor for the transition from juvenile to adult in fish, in general, in the context of phenotypic life history plasticity and "stunting" in tilapias. Size at maturity and the estimated asymptotic size decreased with decreasing O-2 concentration, as predicted by Pauly's hypothesis. All fish matured at the same age (18 weeks old), which is in contrast to conventional definitions of stunting. This finding challenges the suggested plasticity in age at first maturity for tilapia. The results also challenge the hypothesis that stunting is a unique recruitment mechanism, as the smaller fish in the group with low oxygen concentration produced smaller and fewer eggs than the larger fish in the group with high oxygen concentration.
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Fish behaviourists are increasingly turning to non-invasive measurement of steroid hormones in holding water, as opposed to blood plasma. When some of us met at a workshop in Faro, Portugal, in September, 2007, we realised that there were still many issues concerning the application of this procedure that needed resolution, including: Why do we measure release rates rather than just concentrations of steroids in the water? How does one interpret steroid release rates when dealing with fish of different sizes? What are the merits of measuring conjugated as well as free steroids in water? In the 'static' sampling procedure, where fish are placed in a separate container for a short period of time, does this affect steroid release and, if so, how can it be minimised? After exposing a fish to a behavioural stimulus, when is the optimal time to sample? What is the minimum amount of validation when applying the procedure to a new species? The purpose of this review is to attempt to answer these questions and, in doing so, to emphasize that application of the non-invasive procedure requires more planning and validation than conventional plasma sampling. However, we consider that the rewards justify the extra effort.
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Eutrophication has been an increasing ecological threat during the past 50 yr in many Scandinavian and Baltic marine waters. Large sedimentary areas are seasonally, or more or less permanently, affected by hypoxia and/or anoxia with devastating effects on the benthic macrofauna in, for example, the Baltic Sea, the Belt Seas and Oresund between Denmark and Sweden, the Kattegat and the Skagerrak coast towards the North Sea. In this review figures for the input of nitrogen and phosphorus to different sea areas are presented, and in several cases also changes of nitrogen and phosphorus concentrations in the water. The nutrient input is related to production levels, and related to macrobenthic infauna. Changes of dominant benthic species, abundance and biomass are presented in relation to both changes in organic enrichment and hypoxia and/or anoxia in time and space. Since the 1950s-60s, the benthic faunal biomass has increased in the Gulf of Bothnia as a result of increased organic enrichment. In the Aland Archipelago, the number of benthic species decreased since the 1970s but abundance and biomass increased. Drifting algae at the sediment surface has also been an increasing problem. The changes were caused by increasing eutrophication. In the Finnish Archipelago Sea, large-scale eutrophication has resulted in periodic bottom water hypoxia and drifting algal mats with negative effects on benthic fauna. In the Gulf of Finland, the benthic fauna has been negatively affected by hypoxic bottom water below 70 in depth since the 1960s, but with a period of improved oxygen conditions during 1987-94. In the Baltic Proper, large sea-bed areas of 70 000-100 000 km(2) below 70-80 in water depth have been more or less hypoxic and/or anoxic since the 1960s with no or reduced sediment-dwelling fauna. This process was a result of increased eutrophication and lack of larger inflows of oxygenated water from the Kattegat. Several coastal areas and larger basins in the southern Baltic (e.g. the Bornholm Basin, the Arkona Basin and the Kiel Bay), have, on occasions, been similarly negatively affected by hypoxic bottom water. Many sedimentary areas below similar to 17 in in the Danish Belt Seas have been affected by seasonal hypoxia since the 1970s with negative consequences for the bottom fauna. On the Danish Kattegat coast, the benthic fauna in the Limfjord, the Mariager fjord and the Roskilde fjord have been particularly negatively affected. In the southeast, open Kattegat, increased input of nutrients in combination with stratification have resulted in seasonal hypoxia since 1980 with negative effects on benthic animals and commercial fish species in most years. Several fjords on the Swedish and Norwegian Skagerrak coast have shown negative temporal trends in bottom water oxygen concentrations, and some of them lack benthic fauna in the deeper parts for several months or more. In this review the temporal development of bottom water hypoxia and/or anoxia is discussed and consequent possible losses of sediment-dwelling faunal biomass are roughly calculated. In total for the areas investigated, the worst years of hypoxia and/or anoxia combined may have reduced the benthic macrofaunal biomass by 3 million t. This loss is partly compensated by the biomass increase that has occurred in well-flushed organically enriched coastal areas. Tolerance of some Baltic species to hypoxia and/or anoxia is discussed and also their different strategies to cope with hypoxia and/or anoxia and H2S.
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The species flock of haplochromine cichlid fishes in Lake Victoria is one of the most extensive and recent radiations of vertebrates known. Over the past 15 years, however, many of the haplochromine cichlid species have vanished, and predation by the introduced Nile perch (Lates niloticus) is thought to be one of the most significant factors underlying this mass extinction. Information on the hypoxia tolerance of haplochromines from Late Victoria is valuable for predicting their response to the increasing anoxia within the lake and in evaluating their potential use of low oxygen regions as refugia from predation by introduced Nile perch. This study examines the response of nine cichlid species from Lake Victoria (eight indigenous, one introduced) and three cichlid species from Late Tanganyika to different low-oxygen regimes under laboratory conditions. Fish were exposed to progressive and acute hypoxia, with and without access to the surface. All species used aquatic surface respiration at very low P-O2. Buccal bubble holding and active swimming at the surface during aquatic surface respiration were used by many species and may serve to increase its efficiency. Lacustrine cichlids endemic to Lake Victoria were more tolerant of hypoxia than ecologically similar species from Lake Tanganyika. The two species ex;unmined that are widespread in a variety of aquatic habitats exhibited a relatively high tolerance to hypoxia with well-developed aquatic surface respiration and bubble-holding capabilities and no loss of equilibrium during progressive hypoxia. Species strongly affected by recent changes in Lake Victoria were not consistently poorer in their hypoxia tolerance than less-affected species. But, two of the less-affected species are inhabitants of shallow, rocky habitats, an environment that may be both rich in oxygen and roell defended against the Nile perch because of the structural complexity of the rocky, littoral area. The generally high levels of hypoxia tolerance in the cichlid species examined from Lake Victoria suggest that these species potentially could use low-oxygen refugia to escape Nile perch predation. Some species that are thought to have disappeared may currently inhabit low-oxygen refugia that have not been adequately sampled
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Observations of male three-spined stickleback (Gasterosteus aculeatus L.) parental care were made in a salt-marsh tide pool at 3-h intervals over 24-h cycles, to determine if male behavior varied in association with diel changes in water temperature and dissolved oxygen concentration. An analysis of egg metabolism in situ revealed positive correlations between rate of egg oxygen consumption and egg age, water temperature, and dissolved oxygen levels, while there was a slight but significant negative correlative with the number of eggs per nest. We found no significant difference when we compared the proportion of time males spent fanning their nests during the day with night levels. However, nocturnal fanning bouts were significantly longer and less numerous than diurnal ones. In contrast to the rest of the 24-h cycle, the males remained inactive between fanning bouts at night, except when exposed to hypoxic conditions
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F1 offspring of the African cichlid Pseudocrenilabrus multicolor victoriae Seegers, 1990 from swamp (low oxygen) and lake (high oxygen) origin were raised under normoxia and submitted to hypoxia acclimation (0.8 ± 0.4 mg·L–1) and normoxia acclimation (7.4 ± 0.3 mg·L–1) for 4 weeks. Haematocrit and lactate dehydrogenase (LDH) specific activities in the liver, white skeletal muscle, heart, and brain were measured. For haematocrit and LDH activities of liver, muscle, and heart, the response to acclimation depended upon population of origin. In general, fish from the swamp population showed a more “typical” hypoxic response (increased haematocrit and LDH activities), whereas fish from the lake population either did not respond or showed the opposite response. The results suggest that populations of P. m. victoriae sampled from habitats with diverse oxygen regimes differ in their physiological and biochemical responses to hypoxia.
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In this review the effects of hypoxia on benthic fauna are summarized and detailed information is given on (1) the impact on community structure and function in fjords, estuaries, coastal and offshore areas (2) behavioural changes (3) recovery processes (4) ecosystem energy flow implications, and (5) tolerance in experimental studies. There is no other environmental variable of such ecological importance to coastal marine ecosystems that has changed so drastically in such a short period as dissolved oxygen. While hypoxia and anoxic environments have existed through geological time, their occurrence in shallow coastal and estuarine areas appears to be increasing, most likely accelerated by human activities. Ecological problems associated with the occurrence of low oxygen are increasing on a global scale. The oxygen budgets of most major estuarine and coastal ecosystems have been adversely affected mainly through the process of eutrophication, which acts as an accelerant or enhancing factor to hypoxia and anoxia, and when coupled with adverse meteorological and hydrodynamic events, hypoxia increases in frequency and severity. The area of hypoxic and anoxic bottom water is even increasing within systems that historically are considered oxygen stressed. Many ecosystems that are now severely stressed by hypoxia appear to be near or at a threshold. Should oxygen concentrations become slightly lower, catastrophic events may overcome the systems and alter the productivity base that leads to fisheries species. Examples of such events are becoming increasingly common. At what point permanent damage will result is difficult to say. To date there is no large system that has recovered after development of persistent hypoxia or anoxia. The only exception may be small systems where pollution inputs have ceased and recovery initiated from surrounding non-affected areas. The expanding occurrence of hypoxia and anoxia continues to bring about significant structural changes in benthic communities and to affect benthic-pelagic coupling. Restoring ecosystem balance and reversing the trend of increasing hypoxia and anoxia will require dealing with the global problem of coastal eutrophication and determining how to reduce the production of organic matter in sensitive estuarine and coastal areas.
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Growth, size at maturity, gonadosomatic index (GSI), egg size, and absolute fecundity of Nile tilapia (Oreochromis niloticus) were significantly affected by oxygen levels (1.5 +/- 1.0, 2.8 +/- 1.4, and 6.0 +/- 1.8 mg center dot L-1) in a controlled experiment designed to test the hypothesis (D. Pauly. 1984. J. Cons. Int. Explor. Mer, 41: 280-284) that O-2 is the controlling factor for the transition from juvenile to adult in fish, in general, in the context of phenotypic life history plasticity and "stunting" in tilapias. Size at maturity and the estimated asymptotic size decreased with decreasing O-2 concentration, as predicted by Pauly's hypothesis. All fish matured at the same age (18 weeks old), which is in contrast to conventional definitions of stunting. This finding challenges the suggested plasticity in age at first maturity for tilapia. The results also challenge the hypothesis that stunting is a unique recruitment mechanism, as the smaller fish in the group with low oxygen concentration produced smaller and fewer eggs than the larger fish in the group with high oxygen concentration.
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In this study we investigate the possible role of phenotypic plasticity and genetic assimilation in the process of adaptation and evolutionary change in the cichlid Pseudocrenilabrus multicolor victoriae. In the field we compared a population of a stable hypoxic habitat with one of a stable well-oxygenated habitat. In the laboratory, we compared individuals from the same mother raised under hypoxic or well-oxygenated conditions to examine phenotypic plasticity. Morphological parameters of three categories were measured: (a) the gill apparatus, (b) the surrounding structural elements, and (c) the outer shape of the fish. Swamp-dwelling fish had a 29% greater total gill surface area than fish from the well-oxygenated habitat due to their larger gill filament length and greater lamellar area. In the plasticity experiment, total gill surface area was 18% greater in the hypoxia group due to a larger number of longer filaments. Surrounding elements and outer shape also differed between the field populations and between fish grown under hypoxic and well-oxygenated conditions, but there was disparity between the field results and the plasticity experiment. The disparity between field and experimental fish may be due to: (a) differences in selection pressures between populations, (b) different constraints for genetic and plasticity changes, or (c) selection against plastic responses to hypoxia. Our results suggest that both (a) and (c) are involved.
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In this study we explore the possible role of phenotypic plasticity in the process of adaptation and evolutionary change in the African cichlid Pseudocrenilabrus multicolor victoriae. Parental fish were collected from a hypoxic swamp, a lake ecotone, and a river in Uganda. Broods (F1) were split and grown under hypoxia or normoxia. We measured mor-phological parameters of the gill apparatus, structural elements surrounding the gills, brain mass, and body shape. Most traits showed substantial plasticity in response to the rearing environment. Population effects were evident for the gill ap-paratus, surrounding elements, body shape, and brain size; however, brain size was the only trait to exhibit variation in plasticity among populations; fish of swamp origin showed no plasticity and fish of river and lake origin exhibited smaller brain size under hypoxia. We interpret these patterns as consistent with genetic assimilation via canalization (brain) or via a shift in the norm of reaction (other traits).
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Eutrophication has been an increasing ecological threat during the past 50 yr in many Scandinavian and Baltic marine waters. Large sedimentary areas are seasonally, or more or less permanently, affected by hypoxia and/or anoxia with devastating effects on the benthic macrofauna in, for example, the Baltic Sea, the Belt Seas and Öresund between Denmark and Sweden, the Kattegat and the Skagerrak coast towards the North Sea. In this review figures for the input of nitrogen and phosphorus to different sea areas are presented, and in several cases also changes of nitrogen and phosphorus concentrations in the water. The nutrient input is related to production levels, and related to macrobenthic infauna. Changes of dominant benthic species, abundance and biomass are presented in relation to both changes in organic enrichment and hypoxia and/or anoxia in time and space. Since the 1950s-60s, the benthic faunal biomass has increased in the Gulf of Bothnia as a result of increased organic enrichment. In the Åland Archipelago, the number of benthic species decreased since the 1970s but abundance and biomass increased. Drifting algae at the sedi-ment surface has also been an increasing problem. The changes were caused by increasing eutrophication. In the Finnish Archipelago Sea, large-scale eutrophication has resulted in periodic bottom water hypoxia and drifting algal mats with negative effects on benthic fauna. In the Gulf of Finland, the benthic fauna has been negatively affected by hypoxic bottom water below 70 m depth since the 1960s, but with a period of improved oxygen conditions during 1987-94. In the Baltic Proper, large sea-bed areas of 70 000-100 000 km 2 below 70-80 m water depth have been more or less hypoxic and/or anoxic since the 1960s with no or reduced sediment-dwelling fauna. This process was a result of increased eutrophication and lack of larger inflows of oxygenated water from the Kattegat. Several coastal areas and larger basins in the southern Baltic (e.g. the Bornholm Basin, the Arkona Basin and the Kiel Bay), have, on occasions, been similarly negatively affected by hypoxic bottom water. Many sedimentary areas below -17 m in the Danish Belt Seas have been affected by seasonal hypoxia since the 1970s with negative consequences for the bottom fauna. On the Danish Kattegat coast, the benthic fauna in the Limfjord, the Manager fjord and the Roskilde fjord have been particularly negatively affected. In the southeast, open Kattegat, increased input of nutrients in combination with stratification 427 KAR IN KARLSON, RUTGER ROSENBERG & ERIK BONSDORFF have resulted in seasonal hypoxia since 1980 with negative effects on benthic animals and commercial fish species in most years. Several fjords on the Swedish and Norwegian Skagerrak coast have shown negative temporal trends in bottom water oxygen concentrations, and some of them lack benthic fauna in the deeper parts for several months or more. In this review the temporal development of bottom water hypoxia and/or anoxia is discussed and consequent possible losses of sediment-dwelling faunal biomass are roughly calculated. In total for the areas investigated, the worst years of hypoxia and/or anoxia combined may have reduced the benthic macrofaunal biomass by 3 million t. This loss is partly compensated by the biomass increase that has occurred in well-flushed organically enriched coastal areas. Tolerance of some Baltic species to hypoxia and/or anoxia is discussed and also their different strategies to cope with hypoxia and/or anoxia and H 2 S.
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Winterkill lakes often have a characteristic fish community, presumably composed of species able to survive winter hypoxia. Our research on a small winterkill lake in northern Wisconsin indicates that fishes common in winterkill lakes have behavioral adaptations for tolerating or avoiding winter hypoxia. We examined the distribution of fishes within the lake during one winter (December through May), and fish migrations into and out of the lake for two consecutive years. As DO within the lake declined in late fall, adult-sized fishes of four species, brook stickleback, finescale dace, redbelly dace, and fathead minnow, moved to the ice-water interface where DO levels were highest. Stickleback, and to a lesser extent, fathead minnows, also moved toward the more highly oxygenated water near the inlet. During the first year, young-of-the-year fishes of blacknose shiner, Iowa darter, redbelly dace, and fathead minnow, avoided hypoxic conditions by emigrating from the lake via the outlet stream in late fall and early winter while DO within the lake was still relatively high. Blacknose shiner, redbelly dace, and fathead minnow returned to the lake in spring. Almost no fishes were trapped leaving the lake in the second fall-winter season. Central mudminnows neither moved to the ice-water interface nor emigrated from the lake as DO dropped. Mudminnows survive winter hypoxia by breathing oxygen-containing bubbles trapped beneath the ice. These relatively simple behavioral adaptations allow fishes to survive or avoid hypoxic conditions lethal to other species and may help explain the consistency in fish communities of winterkill lakes.
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We evaluated the effects of dissolved oxygen on offspring survival, parental costs, and the pattern of parental care in Florida flagfish, Jordanella floridae (Cyprinodontidae). Specifically, we quantified (1) embryonic development and survival in the absence of parental care, (2) behavior of non-reproductive adults, and (3) behavior of parental males across a gradient in dissolved oxygen. Embryo developmental rates and survivorship increased with dissolved oxygen, with a relatively sharp increase in survival between medium and high oxygen treatments. Non-reproductive adults increased their frequency of aquatic surface respiration, reduced overall activity, and increased opercular beat rate as oxygen declined, suggesting increased costs of activity with reduced oxygen. Taking these cost measures together, costs appear to increase slowly as oxygen starts to decline and then increase sharply as conditions approach hypoxia. In contrast, parental effort increased gradually with dissolved oxygen. We conclude that the increase in care from low to medium oxygen primarily results from a sharp decline in physiological costs, whereas the continued increase in care from medium to high oxygen primarily results from an increase in offspring value. In addition, our results highlight that the benefits of fanning for offspring are not well understood and that they may increase with oxygen, contrary to what has been previously assumed.
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Despite uncertainty in all levels of analysis, recent and long-term changes in our climate point to the distinct possibility that greenhouse gas emissions have altered mean annual temperatures, precipitation and weather patterns. Modeling efforts that use doubled atmospheric CO2 scenarios predict a 1–7°C mean global temperature increase, regional changes in precipitation patterns and storm tracks, and the possibility of “surprises” or sudden irreversible regime shifts. The general effects of climate change on freshwater systems will likely be increased water temperatures, decreased dissolved oxygen levels, and the increased toxicity of pollutants. In lotic systems, altered hydrologic regimes and increased groundwater temperatures could affect the quality of fish habitat. In lentic systems, eutrophication may be exacerbated or offset, and stratification will likely become more pronounced and stronger. This could alter food webs and change habitat availability and quality. Fish physiology is inextricably linked to temperature, and fish have evolved to cope with specific hydrologic regimes and habitat niches. Therefore, their physiology and life histories will be affected by alterations induced by climate change. Fish communities may change as range shifts will likely occur on a species level, not a community level; this will add novel biotic pressures to aquatic communities. Genetic change is also possible and is the only biological option for fish that are unable to migrate or acclimate. Endemic species, species in fragmented habitats, or those in east–west oriented systems will be less able to follow changing thermal isolines over time. Artisanal, commercial, and recreational fisheries worldwide depend upon freshwater fishes. Impacted fisheries may make it difficult for developing countries to meet their food demand, and developed countries may experience economic losses. As it strengthens over time, global climate change will become a more powerful stressor for fish living in natural or artificial systems. Furthermore, human response to climate change (e.g., increased water diversion) will exacerbate its already-detrimental effects. Model predictions indicate that global climate change will continue even if greenhouse gas emissions decrease or cease. Therefore, proactive management strategies such as removing other stressors from natural systems will be necessary to sustain our freshwater fisheries.
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This study quantifies the behavioral response of the widespread mouth brooding African cichlid Pseudocrenilabrus multicolor victoriae to progressive hypoxia. We exposed four gender/stage classes of P. multicolor (males, brooding females, females that had just released young, and non-brooding females) to progressive hypoxia and recorded the percent time spent using aquatic surface respiration (surface skimming, ASR) and gill ventilation rates. This was done for fish collected from three sites in Uganda (lake, swamp, and river) after long-term acclimation to normoxia. There was no effect of site of origin on response to hypoxia, but ASR thresholds did differ between gender/stage classes. The oxygen level (threshold) at which spent 10, 50, and 90% of their time at the surface using ASR was much higher for brooding females than for males, whereas ASR thresholds did not differ between non-brooding females and males. Similarly, the level at which ASR was initiated was much higher in brooding females than males, but did not differ between males and non-brooders, or between males and females than had just released young. The rate of gill ventilation dropped significantly in males and all stages of females after initiation of ASR, suggesting that surface skimming increases efficiency of oxygen acquisition. These results suggest that mouth brooding in female P. multicolor ASR improves oxygen uptake but imposes a cost in terms of time spent at the water surface, and this may affect maternal predation risk in low-oxygen habitats.
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Fishes employ many and diverse strategies to increase oxygen transfer from the environment to their tissues and/or avoid problems associated with hypoxia. Some of these responses can be activated quickly (e.g., hours, days), whereas others are developmentally plastic and/or genetically fixed. Short‐term physiological and biochemical responses provide regulatory mechanisms to deal with variable oxygen in habitats. Behavioral responses can provide additional flexibility to mitigate exposure to hypoxic stress, and many occur at levels of aquatic oxygen availability far higher than lethal levels. Fish may avoid hypoxic areas through movement or they may compensate for hypoxia through air‐breathing or aquatic surface respiration (ASR), ventilating their gills with water from the air–water interface. As a result, behavioral responses to hypoxia can influence other critical components of the behavior of fishes in their environment, including habitat use and selection, predator–prey interactions, competitive interactions, and patterns of aggregation. In this chapter, we review behavioral responses to hypoxia, including aquatic surface respiration, air‐breathing, changes in spontaneous activity, and parental care. We then consider the role of hypoxia in modulating ecological interactions, in particular the interaction between predator and prey. Hypoxic alterations to predator–prey interactions can influence other components of the food web and assemblage structure; so predicting whether predator or prey is the beneficiary of hypoxic stress is fundamental to understanding community level impacts of hypoxia, whether natural or anthropogenically induced.
Article
Plasma estradiol-17 beta and testosterone levels were assessed by radioimmunoassay during the sexual maturation of female amago salmon (Oncorhynchus rhodurus). Estradiol-17 beta levels gradually increased during vitellogenesis (June to September), reached a peak in September (about 16 ng/ml) and rapidly decreased in mature and ovulated fish (about 3-4 ng/ml) in October. The seasonal pattern of plasma testosterone levels lagged behind and followed that of estradiol-17 beta during vitellogenesis, but levels remained high in mature and ovulated fish (90-110 ng/ml). Estradiol-17 beta levels and the gonadosomatic index (GSI) values correlated well during vitellogenesis: GSI values showed a linear increase, and reached a peak (29.9 +/- 1.4) in October. Values were extremely low in ovulated fish (1.2 +/- 0.2). In vitro production of estradiol-17 beta and testosterone by ovarian follicles in response to partially purified chinook salmon gonadotropin (SG-G100) was examined monthly using 18-h incubations. Throughout the vitellogenic period SG-G100 stimulated both estradiol-17 beta and testosterone production: the steroidogenic response of follicles increased from June (about 2 ng/ml estradiol-17 beta; 0.1 ng/ml testosterone) to September (about 10 and 14 ng/ml, respectively). In October full-grown immature follicles which could be induced to mature in vitro by hormone treatment produced large amounts of testosterone (about 130 ng/ml) but not estradiol-17 beta. Postovulatory follicles also produced testosterone but the values were low (10 ng/ml) compared with full-grown immature follicles. Very low levels of estradiol-17 beta were produced by postovulatory follicles.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Northern pike (Esox lucius), yellow perch (Perca flavescens), and bluegill (Lepomis macrochirus), were exposed to successively lower oxygen concentrations 4.0, 2.0, 1.0, 0.5, and 0.25 mg/liter) each day for five days in aquaria sealed above with simulated "ice." Water temperature varied from 2.5 to 4.0 C and light intensity and photoperiod simulated conditions in an ice-covered lake. Gill ventilation rates increased in response to lowered oxygen, doubling for bluegill and yellow perch but quadrupling for northern pike. Maximum ventilation rates occurred at 0.5 mg/liter D.O. for northern pike and yellow perch and at 1.0 mg/liter D.O. for bluegill. Locomotory activity was greatest at 0.25 mg/liter D.O. for northern pike but at 0.5 mg/liter D.O. for yellow perch and bluegill. Northern pike and yellow perch began to move toward the ice at 0.5 mg/liter D.O. At 1.0 mg/liter D.O., bluegill kept sinking to the bottom of the aquaria; they continually made forays upward only to sink again. Northern pike and yellow perch nosed at the under surface of the ice at the lowest oxygen concentrations while bluegill seldom did. The fish never aggregated more than 10 percent of the time even at the lowest concentrations of dissolved oxygen. Almost all northern pike and yellow perch were still alive at 0.25 mg/liter D.O. while all bluegill were dead. Evidently northern pike are best adapted for survival in winterkill lakes and bluegill the least. The upward movement takes the fish to the highest oxygen available in the immediate vicinity. Detection of an oxygen gradient is not a requirement of this response because in the aquaria the fish move to the ice at low oxygen concentrations in absence of a gradient. High free CO2 and dissolved H2 S are also not necessary to stimulate or orient the upward movement. Increased locomotory activity, if coupled to reduced activity when respiratory distress is alleviated, also provides an effective mechanism for locating higher oxygen. The increases in gill ventilation have obvious survival value.
Article
Although reduced levels of oxygen may act primarily as a non-directional stimulus for fish and cause increased random swimming activity, prompt avoidance of oxygen-deficient water has also been reported for some species. In this study goldfish were confined in a tube through which deoxygenated water flowed at a rate of 500 ml/min. If the fish responded by swimming forward in the chamber until its head passed through an archway leading to the inlet end of the tube, it received a 10-sec. flow of aerated water. To maintain this flow the fish was required to move forward and backward in the tube, and most animals began to respond steadily within 5 min. Although the conditions of the experiment were highly artificial, such behavior appears to have physiological significance since it represents a means whereby the fish can achieve some regulation of its respiratory environment.
Article
The cycles of killifishes of the genus Crenichthys were studied, using trap capture rates and sound volumes as indices of activity. When other factors are optimal, the fish are less active in the dark than in the light, regardless of clock time. A variety of environmental parameters could probably alter the cycles when any one factor is unfavorable. Low concentrations of dissolved oxygen result in reduced activity. Such reduction can be effected at one site where dissolved oxygen is limited, while nearby populations are active in localities that have more dissolved oxygen. Apparently at 32 C activities are adversely affected by oxygen supplies below 2 ppm.
Article
Respiratory characters of three east African haplochromine cichlid species that differ in their use of hypoxic wetlands were examined to consider the potential of dissolved oxygen as one factor affecting habitat use. All three species had a large gill surface area, ranging from the 67th (Pseudocrenilabrus multicolor victoriae) to 98th (Astatotilapia velifer) percentile of the known gill size range for freshwater fishes. Pseudocrenilabrus multicolor victoriae was the most tolerant to hypoxia exhibiting the lowest aquatic surface respiration (R(s)) thresholds and lowest critical oxygen tension of the three species. Astatotilapia velifer had the highest ASR thresholds, gill ventilation rates, and level of surface activity of the three species, indicating a relatively low tolerance to hypoxia. Prognathochromis venator was intermediate in its response to hypoxia. These findings are discussed in light of survivorship and distribution patterns of these species following Nile perch introduction into Lake Nabugabo.
Article
The ability to tolerate hypoxia in some haplochromine cichlid fishes contributes to the richness of habitats occupied by the lineage and may be important in interlacustrine dispersal through swampy channels. Lacustrine members of the genus Astatotilapia tend to be ecologically plastic but are rarely encountered in the interior of dense swamps. A notable exception is seen in the swamp corridor that joins Lake Kabaleka with Lake George, Uganda, where one species (Astatotilapia ‘wrought-iron’) is abundant, and a second species, A. aeneocolor, is rare. Both species are abundant in the open waters of the main lake. In this paper, we compare physiological (oxygen consumption) and behavioral indicators of hypoxia tolerance between A. ‘wrought-iron’ from swamp and open-water habitats and between the two species of Astatotilapia. When exposed to progressive hypoxia, all fish used aquatic surface respiration (ASR); however, swamp-dwelling A. ‘wrought-iron’ showed lower gill ventilation rates prior to the initiation of ASR, higher pre-ASR aggression rates, higher swimming speed during ASR, and a higher rate of bubble exchange than both the open-water group of A. ‘wrought-iron’ and A. aeneocolor. These differences may reflect interpopulational variation in selection pressure for low-oxygen tolerance between swamp and open-water habitats. Several lines of evidence suggest that A. ‘wrought-iron’ was in general more hypoxia tolerant than A. aeneocolor. These include a lower ASR90 threshold, a drop in gill ventilation rate with the onset of ASR, and lower rate of equilibrium loss under extreme hypoxia in A. ‘wrought-iron’. The routine metabolic rate and critical oxygen tension did not differ between swamp-dwelling and open-water A. ‘wrought-iron’, or between A. ‘wrought-iron’ and A. aeneocolor. Comparative data on the ASR thresholds and critical oxygen tensions of the Astatotilapia species from Lake Kabaleka and other East African cichlids suggest intermediate hypoxia tolerance. Nevertheless, our study suggests that some generalized lacustrine haplochromines may ‘leak’ through swamp corridors even under relatively extreme conditions.
Article
The objectives were to investigate the changes in gonadal histology and plasma levels of gonadal steroids from the bisexual to the male phase in the juvenile male black porgy, Acanthopagrus schlegeli. The reproductive cycle in the adult females was also studied. The gonad consisted mainly of testicular tissue at 5 months of age. The ovarian tissue in the stage of primary oocytes was well developed at 7 months of age. The gonad underwent an intensive spermatogenesis at 9 months of age. During the first and second spawning season, the testicular tissue was dominant, which made the fish male. The ovarian tissue became dominant at 18 months of age during the non-spawning season. The chronological order of histological features in black porgy was suggested to be testicular, bisexual, male, bisexual, male, and female. Maximum plasma levels of estradiol-17β and testosterone occurred simultaneously before the first spawning season in juvenile males and might have an important function in spermatogenesis. For females, gonadosomatic index, oocyte diameter, and levels of estradiol-17β and testosterone increased during the spawning season. Peak levels of progesterone and 17α-hydroxyprogesterone were not observed in juvenile males and adult females during the spawning season.
Article
In this review the effects of hypoxia on benthic fauna are summarized and detailed information is given on: the impact on community structure and function in fjords, estuaries, coastal and offshore areas; behavioural changes; recovery processes; ecosystem energy flow implications; tolerance in experimental studies. -from Authors
Article
There is increasing concern that certain chemicals in the aquatic environment can disrupt endocrine systems, leading to reproductive impairment and threatening survival of wild populations of invertebrates, fish, bird, reptiles, and wildlife. For the first time, we report that hypoxia is also an endocrine disruptor and poses a significant threat to the reproduction and hence sustainability of fish populations. Serum levels of testosterone, estradiol, and triiodothyronine significantly decreased in carp (Cyprinus carpio) upon chronic exposure to hypoxia. These hormonal changes were associated with retarded gonadal develop ment in both male and female carp, reduced spawning success, sperm motility, fertilization success, hatching rate, and larval survival, indicating that adverse effects of hypoxia on reproductive performance resulted from endocrine disruption. Since aquatic hypoxia commonly occurs over thousands of square kilometers in aquatic systems worldwide, our results imply that endocrine disruption and reproductive impairment in fish may be a widespread environmental problem.
Article
The behavioural response of egg-tending males from parapatric fluvial and lacustrine populations of a landlocked goby Rhinogobius sp. (the orange form) to oxygen stress was compared in laboratory experiments. The natural spawning locations of these populations (rapids of tributary rivers and lakeshore of Lake Biwa, respectively) differ in dissolved oxygen concentration and its variability. Males of both populations spent a longer period of time in fanning behaviour under low dissolved oxygen conditions (4·5–5·0 mg l−1), where >90% of eggs without paternal care died before reaching eyed stage, relative to fully saturated dissolved oxygen conditions (8·0–8·5 mg l−1). Lacustrine males, who occasionally encounter oxygen stress (<2 mg l−1) in their natural habitat, fanned eggs for a longer time period than fluvial males. The time difference in fanning behaviour between the two oxygen conditions was greater for lacustrine than fluvial males. Survival rate in the lower oxygen condition was higher for eggs tended by lacustrine males than those tended by fluvial males, probably due to this difference in fanning activity. These results showed that the response to oxygen stress differs between the two populations and, moreover, as both populations behaved adaptively in responding to the reduction in dissolved oxygen, contiguous habitats may have distinct natural selective pressures. It is suggested that regulation of egg fanning activity is strongly favoured by natural selection in unpredictable environments.
Article
Many small species of fish are found in the stream/swamp systems that flow into Lake Victoria. One such system, in Uganda, was inhabited permanently by only one species, although others ran into the stream when it was flooded in the rainy seasons. Other fishes were confined to the lower reaches near the mouth, but never moved far upstream.Studies on the biology of these fishes indicate that reproductive behaviour is generally confined to the rains in all species, the cyprinids using the system especially for breeding purposes at these times. Factors other than sexual state, such as feeding habits, vary little between fish from the river and those from the lake.Experiments show that there is a change in the sexual state of the females of one species during the journey upriver, indicating the importance of this activity in the life cycle of the migratory fish.The young of the cyprinids first appear in the up-river swamps. Here they grow, migrating to the river and moving downstream to enter the lake after periods of time that are characteristic for each species. This distinctiveness in timing was also found for the other fishes that inhabit the system, and it suggests that downstream migration is controlled by changes in the physiological state of the fish with age.
Article
Seven ovarian stages are described in summer flounder Paralichthys dentatus. In the prespawning season plasma oestradiol levels increased in maturing fish with lipidogenic oocytes and gonadosomatic index increased in fish undergoing vitellogenesis. Atretic oocytes present in the postspawning season indicated which individuals may have spawned. The pattern of oocyte development is similar to that of other flatfishes and some teleosts. The summer flounder was unusual in having a long lipid uptake phase (oocyte diameter up to 301 μm) prior to any indication of vitellogenin (yolk protein) uptake. This information will be useful in the construction of an updated maturity schedule for the wild population.
Article
Measurements were made of plasma 11-ketotestosterone and testosterone in control and sex-reversed male rainbow trout, before and during their first spawning season (winter 1978/1979). Plasma concentrations of both androgens (in both groups) were 2–3 ng ml-1 in January 1978 (apart from some precocious spawners), rose slowly to 9–11 ng ml-1 in April and July and then increased rapidly to 100–150 ng ml-1 in November. From this time, testosterone levels declined but those of 11-ketotestosterone continued to rise to a peak of 260 ng ml-1 in February 1979. No significant differences in hormone levels were found between control male and masculinized female fish.
Article
Lake Nabugabo is widely known as the home of endemic cichlid fishes, but virtually nothing has been published regarding the limnological setting in which those species evolved during the late Holocene. Analysis of a 2.7 m long sediment core collected near the center of the lake suggests that Nabugabo was first isolated from Lake Victoria ca. 5000 calendar years ago, which would make it ca. 1000 years older than was previously believed. The lake apparently shrank significantly around 2600 and 2000 years ago during century-scale droughts, but it did not dry out at any point in its history. The inferred lake-level history of Nabugabo is generally consistent with Holocene paleoclimate records from the adjacent Lake Victoria basin, and suggests that biota in this lake were subjected to at least two major environmental changes during the last 5 millenia.
Article
This study evaluated whether the African cyprinid Barbus neumayeri from Rwembaita Swamp (low-oxygen) and Njuguta River (high-oxygen) in the Kibale National Park, Uganda differed in traits related to aerobic and anaerobic metabolic potential. Haematocrit was measured as an index of blood oxygen-carrying capacity, and tissue activities and isozyme composition of lactate dehydrogenase (LDH) were measured as indices of tissue anaerobic capacity. To address whether site-dependent differences were acute responses v. longer-term adjustments to environ-mental conditions, these variables were measured in fish sampled shortly after collection and after laboratory maintenance under well-aerated conditions. In fish sampled in the field, those from the low-oxygen site had significantly higher haematocrit, but this difference disappeared after long-term laboratory maintenance. In contrast, fish from the low-oxygen site had higher liver LDH activities than fish from the high-oxygen site, and this difference persisted during laboratory maintenance. Polymorphism was detected at both the LDH-A and LDH-B loci, and genotype frequencies for LDH-B differed significantly between collection sites. These results demonstrate physiological, biochemical and genetic differences in B. neumayeri from habitats differing in dissolved oxygen availability and suggest both acute and long-term responses to local environmental conditions.
Article
Cortisol is an important indicator of health and behavioral state in fishes, and is produced in response to stressors including confinement, handling and social conflict. An inherent dif-ficulty in measuring circulating cortisol is the implementation of invasive procedures that can be potent stressors. Recent studies show that cortisol can be reliably quantified from fish holding water by placing individuals in a small beaker for a predetermined collection period. We investigated whether convict cichlid fish (Amatitlania nigrofasciata) mount a significant stress response to beaker confinement and whether they habituate to the collection method. We also determined the relationship between plasma and water-borne cortisol, and changes in cortisol release rates following handling and cortisol administration. Initial beaker expo-sure induced high cortisol release rates but cichlids quickly habituated after 3–4 exposures. We revealed significant positive correlations between plasma and water-borne cortisol, and marked increases in water-borne cortisol release rates after cortisol injection that persisted for between 4 and 24 h, depending on the dosage. In conclusion, we provide convincing evidence for the utility and validity of the water-borne collection method to measure cortisol release rates in convict cichlids.
Article
To test whether patches of papyrus swamp contribute to diversification of populations of non-air-breathing fishes, the gill morphology of Barbus neumayeri was compared between a papyrus swamp and several tributaries which differed in oxygen regime. Total gill filament length differed among sites and was negatively related to dissolved oxygen availability, supporting strong selection pressure for low-oxygen tolerance in the swamp interior. Among recaptures of marked B. neumayeri over a 4·5-year period among the focal swamp and connected stream and river sites, 93% of fish were recovered at the site of capture. Some of the individuals that moved crossed physicochemical gradients and traversed long distances within the swamp/stream system. This movement rate would theoretically be sufficient to homogenize gene frequencies among populations. However, randomly amplified polymorphic DNA (RAPD) markers indicated significant genetic differentiation among sites and no relationship between genetic differences and geographical distances among sites suggesting habitat-specific selection pressures on dispersers, rather than insufficient dispersal.
Article
Abstract –  This study quantified the seasonal pattern of reproduction in a swamp-dwelling population of the African cichlid Pseudocrenilabrus multicolor victoriae. In the hypoxic waters of the Lwamunda Swamp, Uganda, P. multicolor was reproductively active throughout the year, even during the peak of the dry seasons. However, the degree of activity was seasonal, with rainfall providing a predictor of the percentage of ripe, mature females. There was no correlation between aquatic oxygen availability dissolved oxygen (DO) and either adjusted mean gonad mass or percentage of mature females, suggesting that DO is not limiting reproductive activity in this system. Reproductively mature females were larger during drier periods and may maximise their lifetime reproductive success by producing young throughout the year; but with a lower brooding efficiency. A comparison with Welcomme’s (1969) study of a river-swamp system feeding Lake Victoria suggests that reproductive patterning is variable among populations of P. multicolor and may reflect adaptive response to chronically hypoxic conditions in the Lwamunda Swamp.
Article
Respiratory characters of three east African haplochromine cichlid species that differ in their use of hypoxic wetlands were examined to consider the potential of dissolved oxygen as one factor affecting habitat use. All three species had a large gill surface area, ranging from the 67th (Pseudocrenilabrus multicolor victoriae) to 98th (Astatotilapia velifer) percentile of the known gill size range for freshwater fishes. Pseudocrenilabrus multicolor victoriae was the most tolerant to hypoxia exhibiting the lowest aquatic surface respiration (Rs)thresholds and lowest critical oxygen tension of the three species. Astatotilapia velifer had the highest ASR thresholds, gill ventilation rates, and level of surface activity of the three species, indicating a relatively low tolerance to hypoxia. Prognathochromis venator was intermediate in its response to hypoxia. These findings are discussed in light of survivorship and distribution patterns of these species following Nile perch introduction into Lake Nabugabo.
Article
The species flock of haplochromine cichlid fishes in Lake Victoria is one of the most extensive and recent radiations of vertebrates known. Over the past 15 years, however, many of the haplochromine cichlid species have vanished, and predation by the introduced Nile perch (Lates niloticus) is thought to be one of the most significant factors underlying this mass extinction. Information on the hypoxia tolerance of haplochromines from the Lake Victoria is valuable for predicting their response to the increasing anoxia within the lake and in evaluating their potential use of low oxygen regions as refugia from predation by introduced Nile perch. This study examines the response of nine cichlid species from Lake Victoria (eight indigenous, one introduced) and three cichlid species from Lake Tanganyika to different low-oxygen regimes under laboratory conditions. Fish were exposed to progressive and acute hypoxia, with and without access to the surface. All species used aquatic surface respiration at very low Po2. Buccal bubble holding and active swimming at the surface during aquatic surface respiration were used by many species and may serve to increase its efficiency. Lacustrine cichlids endemic to Lake Victoria were more tolerant of hypoxia than ecologically similar species from Lake Tanganyika. The two species examined that are widespread in variety of aquatic habitats exhibited a relatively high tolerance to hypoxia, with well-developed aquatic surface respiration and bubble-holding capabilities and no loss of equilibrium during progressive hypoxia. Species strongly affected by recent changes in Lake Victoria were not consistently poorer in their hypoxia tolerance than less-affected species. But, two of the less-affected species are inhabitants of shallow, rocky habitats, an environment that may be both rich in oxygen and well defended against the Nile perch because of the structural complexity of the rocky, littoral area. The generally high levels of hypoxia tolerance in the cichlid species examined from Lake Victoria suggest that these species potentially could use low-oxygen refugia to escape Nile perch predation. Some species that are thought to have disappeared may currently inhabit low-oxygen refugia that have not been adequately sampled. Tolerancia a la hipoxia en cíclidos del Africa oriental: Refugios con bajo contenido de oxígeno en el lago Victoria Resumen: El grupo de especies de peces cíclidos haplocromínidos del lago Victoria es una de las radiaciones de vertebrados más recientes y extensivas de la que se tenga conocimiento. Sin embargo, a lo largo de los últimos 15 años, muchas de las especies de cíclidos haplocromínidos han desaparecido, y la predación por una especie introducida, la perca del Nilo (Lates niloticus) es considerada como uno de los factores más significativos que contribuyeron a esta extinción masiva. La información sobre la tolerancia a la hipoxia de los haplocromínidos del lago Victoria es valiosa para predecir sus respuestas a la anoxia en aumento dentro del lago y en la evaluación del uso potencial de regiones con bajo contenido de oxígeno como refugios contra la predación por parte de la perca del Nilo. Este estudio examina la respuesta de nueve especies de cíclidos del lago Victoria (ocho indígenas y una introducida) y tres especies de cíclidos del lago Tanganica bajo distintos regímenes de bajo contenido en oxígeno en condiciones de laboratorio. Los peces fueron expuestos a una hipoxia progresiva y aguda, con o sin acceso a la superficie. Todas las especies usaron respiración de superficie cuando los niveles de Po2 eran muy bajos. Muchas especies usaron la retención de burbujas en la boca y la natición activa en la superficie durante la respiración de superficie, las cuales podrían servir para aumentar su eficiencia. Los cíclidos lacustres endémicos al lago Victoria fueron más tolerantes a la hipoxia que las especies ecologicamente similares del lago Tanganica. Las dos especies examinadas que tienen amplia distribución en una variedad de hábitats acuáticos exhibieron una tolerancia relativamente alta a la hipoxia, con respiración de superficie y capacidad para la retención de burbujas bien desarrolladas y sin ninguna pérdida en el equilibrio durante la hipoxia progresiva. Las especies fuertemente afectadas por cambios recientes en el lago Victoria no fueron consistentemente más pobres en su tolerancia a la hipoxia que las especies menos afectadas. Sin embargo dos de las especies menos afectadas son residentes de hábitats rocosos someros, un ambiente que podría ser rico en oxígeno y podría estar resguardado de la perca del Nilo debido a la complejidad estructural del área litoral rocosa. Los niveles generalmente altos de tolerancia a la hipoxia en las especies de cíclidos del lago Victoria examinadas sugiere que estas especies podrían usar en forma potencial los refugios con bajo contenido de oxígeno para escapar de la predación por parte de la perca del Nilo. Alguna de las especies que se piensa han desaparecido podrían, en la actualidad, residir en refugios con bajo contenido de oxígeno que no han sido muestreados adecuadamente.
Article
This essay reviews the behavioral responses of fish to reduced levels of dissolved oxygen from the perspective of optimization theory as used in contemporary behavioral ecology. A consideration of oxygen as a resource suggests that net oxygen gain per unit of energy expenditure will be the most useful currency for ecological models of breathing. In the process of oxygen uptake, fish always expend energy on perfusion, usually on ventilation and often on locomotion. These costs, and the risk of predation, will vary with oxygen availability and the type of behavioral response shown. The principal categories of behavioral response to reduced external availability of dissolved oxygen are (1) changes in activity, (2) increased use of air breathing, (3) increased use of aquatic surface respiration, and (4) vertical or horizontal habitat changes. Fish should choose whichever combination of responses minimizes the costs of meeting their oxygen demands. A small number of studies provides qualitative support for this prediction.
Article
The nature of the steroids secreted by gonads of fish differs significantly from those of the mammals. The classical teleost steroids, oestradiol, testosterone, 11-ketotestosterone and 17,20P, have been measured in a wide variety of teleosts but do not always reflect biological activities. There is increasing evidence that teleost gonads may produce a number of non-classical steroids which may play an important role in their reproductive biology. Such products include metabolites reduced at C5 to 5 or 5, at C3 to 3 or 3, or hydroxylated at 6-, 7-, or 21. Conjugation, as either glucuronides or sulphates, may contribute either to localization of action within the gonad or to production of pheromones during the immediate pre-spawning period. Although it is often possible only to measure the steroids for which assays are readily available, it is important to recognize that there may be production of steroids that are not detected by such assays, but which nevertheless play a major role in reproductive activity. In evolutionary terms, the teleost hydroxylases probably originated in the very early fishes and show parallels with their analogues in amphibians and mammals. Gene sequencing may reveal a possible common ancestor for all vertebrate 6, 7 and 11-hydroxylases.
Article
Fishes use unimodal water breathing, unimodal air breathing, and a wide range of bimodal combinations of water and air breathing to obtain oxygen. This essay seeks to provide a theoretical framework in which to understand this diversity of respiratory mode. Consideration of oxygen as a resource shows that it is scarce in relation to demand and that an inadequate supply limits activity, growth, reproduction, and ultimately, survival. Thus, there should be strong selective pressure to maximize the efficiency of oxygen uptake. Both water breathing and air breathing require ventilation, circulation, locomotion, and respiratory structures. Each of these components has energy costs and may also be subject to costs in time, materials, or risk of predation. Consideration of these costs reveals that dissolved oxygen concentration and distance from the surface are key environmental determinants. Predation pressure and several morphological and behavioral characteristics may also have an influence. These factors are integrated into a general theory of breathing costs which permits prediction of patterns in respiratory partitioning, habitat selection, the frequency of occurrence of respiratory modes in different habitats and correlations within habitats between behavioral and morphological characteristics and respiratory mode. KeywordsAerial respiration-Air breathing-Aquatic surface respiration-Oxygen-Hypoxia-Respiratory partitioning-Habitat selection-Behavioral ecology
Article
Laboratory experiments were conducted to examine changes in behavior of red hake,Urophycis chuss, under decreasing concentrations of dissolved oxygen (DO). Since the ecological requirements of this species change with age, responses were measured for three different groups: (1) age 0+, = 89 mm total length (TL); (2) age 1+, = 238 mm TL; and (3) age 2–3+, = 397 mm TL. As DO decreased from 8–10 mg l-1 to < 0.5 mg l-1, changes were evident in active time, water column activity, range of horizontal movement, food searching, and agonistic behavior. Age 0+ fish were most sensitive, moving up into the water column and swimming continuously as DO levels fell below 4.2 mg l-1. Age 2–3+ fish were the least responsive, remaining on the substrate and increasing only their range of movement at concentrations below 3 mg l-1. Responses of age 1 + fish were variable, possibly reflecting a transition stage between the younger and older fish. Common to all groups was the decrease and eventual cessation of food searching.
Article
Metabolic activity in livebearing fishes increases with embryonic development so that embryos prior to parturition may have a higher mass-specific oxygen requirement than maternal tissues, temporarily increasing the total routine oxygen requirement of the female. We examined whether females of the livebearing poeciliid Poecilia latipinna (sailfin molly) increase their routine metabolic oxygen consumption during development of their broods. We also quantified effects of gestation on time allocation to aquatic surface respiration (ASR) under hypoxic conditions. Mass-adjusted routine metabolic rate (RMR) of female mollies showed a significant increase during late gestation. The RMR of males did not differ from females that were in their early or mid stage of gestation, but was lower than females in late gestation. Gestating females spent approximately 27% more time conducting ASR than non-gestating females when exposed to chronic hypoxia (1mgl–1), further supporting a brood-related increase in oxygen demand. Increased time allocation to ASR may directly affect maternal predation risk in low-oxygen conditions.
Article
Low dissolved oxygen environments occur in a wide range of aquatic systems, and vary in temporal frequency, seasonality, and persistence. While there have always been naturally occurring low dissolved oxygen habitats, anthropogenic activities related primarily to organic and nutrient enrichment have led to increases in hypoxia and anoxia in both freshwater and marine systems. Lakes and coastal areas with seasonal stratification tend to be highly sensitive to the consequences of anthropogenic nutrient enrichment. Many systems that are currently hypoxic were not reported to have low dissolved oxygen concentrations when first studied. The rapid rise in the number of coastal hypoxic systems lagged about 20 years behind the increased use of industrial fertilizer. The future status of hypoxia and its consequences for fishes will depend on a combination of climate change (primarily from warming, and altered patterns for wind, currents, and precipitation) and land use change (primarily from expanded agriculture and nutrient loadings). If in the next 50 years humans continue to modify and degrade coastal systems as in previous years, human population pressure will likely be the main driving factor in spreading of coastal dead zones and climate change factors will be secondary. Climate forcing, however, will tend to make systems more susceptible to development of hypoxia through direct effects on stratification, solubility of oxygen, metabolism, and mineralization rates, particularly in lakes and semienclosed coastal areas.
Similarly to other vertebrates, the androgen testosterone (T) is present in teleost fishes. In addition, 11-oxygenated androgens, especially 11-ketotestosterone (11KT) are present. 11KT is found in higher levels in the plasma of males than in females, whereas this is usually not the case for T. 11-Oxygenated androgens are generally more effective than T in stimulating secondary sexual characters, reproductive behaviour and spermatogenesis. Nevertheless, receptor-like binding has only reported for T and not for 11KT.