Article

Osmoregulation in elasmobranchs: A review for fish biologists, behaviourists and ecologists

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Abstract

This article provides a broad review of osmoregulation in elasmobranchs for non-specialists, focusing on recent advances. Marine and euryhaline elasmobranchs in seawater regulate urea and other body fluid solutes (trimethylamine oxide (TMAO), Na þ , Cl À) such that they remain hyper-osmotic to their environment. Salt secretions of the rectal gland and excretions in the urine compensate for continuous inward diffusion of environmental salts. Freshwater and euryhaline elasmobranchs in fresh water synthesise less urea and retain less urea and other body fluid solutes compared to marine elasmobranchs and thus have relatively lower osmolarity. Electrolyte uptake at the gills and kidney reabsorption of salts maintain acid–base balance and ionic consistency. The role of the gills, kidney, liver and rectal gland in elasmobranch osmoregulation is reviewed. The ontogeny of osmoregulatory systems in elasmobranchs and the contribution of drinking and eating processes in maintaining osmotic consistency are discussed. Recommendations for future research are presented.

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... To generate osmoregulatory capacity and homeostasis maintenance metrics, urea and phosphorus concentrations were determined in serum. Sharks are ureotelic and urea plays a key role in osmoregulation (Hammerschlag, 2006). When allostatic overload occurs and homeostatic balance is lost, alterations in urea concentrations are observed (Wosnick et al., 2017). ...
... The rectal gland plays an important role in shark osmoregulation and associated homeostatic balance (Hammerschlag, 2006;Ballantyne and Fraser, 2012). The accumulation of Hg in the rectal gland found herein (Table 1) may be related to its high vascularization, suggesting target organ concerning metal toxicity. ...
... One of the main roles of gills in sharks is to maintain the acid-basic balance and prevent systemic acidosis or alkalosis (Shuttleworth, 1988). Additionally, gills play a major role in urea regulation, the main osmolyte for elasmobranch homeostatic balance (Hammerschlag, 2006). Traditionally, Na + /K + ATPase activity and expression are used to evaluate the sublethal effects of exposure to metals in the gills and rectal gland (De Boeck et al., 2001Grosell et al., 2003;Eyckmans et al., 2013). ...
Article
Contamination by metals is among the most pervasive anthropogenic threats to the environment. Despite the ecological importance of marine apex predators, the potential negative impacts of metal bioaccumulation and biomagnification on the health of higher trophic level species remains unclear. To date, most toxicology studies in sharks have focused on measuring metal concentrations in muscle tissues associating human consumption and food safety, without further investigating potential impacts on shark health. To help address this knowledge gap, the present study evaluated metal concentrations in the gills, muscle, liver, and rectal gland of coastal sharks opportunistically sampled from Brazilian waters and tested for potential relationships between metal bio-accumulation and general shark health and homeostatic balance metrics. Results revealed high metal concentrations in all four tissue types, with levels varying in relation to size, sex, and life-stage. Metal concentrations were also associated with serum biomarkers (urea, lactate, ALT, triglycerides, alkaline phosphatase, and phosphorus) and body condition, suggesting potential negative impacts on organismal health.
... They normally maintain their blood osmolarity slightly higher than their environment. This is accomplished by retaining high levels of solutes, such as sodium, chloride, urea and trimethylamine oxide (TMAO) (Evans et al. 2004;Hammerschlag 2006;Anderson et al. 2007). By remaining hyperosmotic compared to the environment, they have less water loss and thus avoid dehydration (Hammerschlag 2006). ...
... This is accomplished by retaining high levels of solutes, such as sodium, chloride, urea and trimethylamine oxide (TMAO) (Evans et al. 2004;Hammerschlag 2006;Anderson et al. 2007). By remaining hyperosmotic compared to the environment, they have less water loss and thus avoid dehydration (Hammerschlag 2006). Because they have the ability of regulating their electrolyte and urea plasma concentrations based on their environment, to higher salinities. ...
... Initially being in an environment with a higher salinity may have resulted in higher concentrations of these ions until the rectal gland could excrete adequate amounts to regulate to the new environment. The kidney is involved with sodium and chloride movement, although to a lesser extent, as well as urea reabsorption and clearance (Evans et al. 2004;Hammerschlag 2006). Some marine elasmobranchs seem to acclimate to lower salinities, not only by increasing urine flow (thus eliminating urea, sodium and chloride), but also possibly by decreasing urea synthesis in the liver (Hazon et al. 2003;Tam et al. 2003;Anderson et al. 2005). ...
... Physiology limits animal distributions (McNab, 2002;Pearse, 1922;Somero, 2012), including stenohaline sharks in coastal ecosystems due to salinity thresholds (Hammerschlag, 2006;McCandless et al., 2007;Whitfield et al., 2012). Juvenile blacktips exhibit a preference for salinities >20 ppt across the Gulf of Mexico (e.g., McCandless et al., 2007;Ward-Paige et al., 2015) and >25 ppt in our study area . ...
... Thus, the distribution of age 0 blacktips should reflect their habitat preferences. Yet, it is unclear if the primary benefit afforded to age 0 blacktips by environmental predictability was physiological homeostasis (Evans et al., 2004;Hammerschlag, 2006;Steiner & Michel, 2007). Comparatively, other factors, like predictability in prey availability or risk attributed to stable salinities, could be more important if prey or predators prefer environmentally stable habitats, thus juvenile blacktips may prefer stable salinities because conditions ecologically optimize growth and survival (Drymon et al., 2013;Lima & Dill, 1990;Speed et al., 2010;Werner & Gilliam, 1984). ...
Article
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Coevolution with predators leads to the use of low‐risk habitats by many prey species, which promotes survival during early developmental phases. These nurseries are valued by conservation and management agencies because of their contributions to adult populations. However, the physical and geographic characteristics, like shallow depths and isolation from other marine habitats, that restrict access to predators and thereby reduce risk to juvenile animals can also limit scientific research. Consequently, many nursery habitats are still unidentified and understudied. Here we used gillnet monitoring from 1982 to 2018 to delineate blacktip shark (Carcharhinus limbatus) nurseries in the north‐western Gulf of Mexico and elucidated their physical, environmental and biological characteristics. Nursery habitats within estuaries (<2% of spatial area) were proximate to the Gulf of Mexico and exhibited significantly lower variability in salinity than non‐nurseries. However, relative abundances of predators and prey were not significant delineators of nursery habitats. As such, food and risk may not influence juvenile blacktip habitat use as expected. Alternatively, reduced osmoregulatory stress attributed to predictable environments likely provides advantageous conditions for blacktips to develop foraging and antipredator tactics, which is vital prior to the winter migration of juvenile sharks into the Gulf of Mexico.
... They use organic osmolytes (urea and trimethylamine oxide) to elevate plasma osmolality to values usually slightly above seawater, and sodium and chloride have a lesser role as the principal extracellular osmolytes. Thus, elasmobranch fishes are typically isosmotic or slightly hyperosmotic to surrounding seawater, primarily attributable to retention of urea (Hammerschlag 2006;Ballantyne 2016). Only the coelacanth among other fishes accumulates urea and TMAO to maintain isosmotic plasma similarly to elasmobranchs (Takei 2000). ...
... Although marine elasmobranchs are not characteristically regarded to drink seawater (and the same could be assumed for coelacanths), euryhaline species drink upon returning to more concentrated seawater as with teleosts (Anderson et al. 2007;Evans and Claiborne 2009). In all sharks, the rectal gland is the principal site of NaCl secretion (Epstein and Silva 2005), the kidneys retain urea, and TMAO (Cohen et al. 1958;Janech et al. 2006), and the gills are the site of acid-base regulation as well as salt uptake in dilute seawater or fresh water (Hammerschlag 2006;Evans and Claiborne 2009;Reilly et al. 2011). ...
Article
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Acquisition of fresh water is important to animals, and is both difficult and critical for species residing in marine environments. Adaptive radiations to fully marine habitats were constrained by the need for fresh water and the capacity of various taxa to adapt physiology to reliance on sources of water other than free drinking water. Here, we review the water relations of marine vertebrates, with an emphasis on drinking and the need to procure fresh water. Numerous marine teleost fishes drink seawater, but some do not, and drinking is more variable and complex than suggested by textbooks. The mechanisms by which fishes and other vertebrates regulate water balance involve the renin–angiotensin and aldosterone endocrine systems, but plasma osmotic and ionic concentrations as well as other chemical signals can also be involved. Multiple mechanisms for stimulation of drinking are operative and diverse among species. Clearly, evolutionary adaptations to environmental salinities can alter drinking behaviors. Marine elasmobranchs do not characteristically drink seawater, but euryhaline species drink upon returning to more concentrated seawater, as with teleosts. Hagfish are osmoconformers, and there is no evidence for drinking. In general, marine reptiles and most marine mammals and seabirds do not drink seawater. Exceptions include sea turtles, cetaceans, and some pinnipeds. Some marine species (e.g., sea snakes) require fresh water that can be acquired from ephemeral rainwater lenses, while others are adapted to utilize dietary and metabolic water. Regardless of drinking behaviors, numerous forms have evolved varied strategies for conserving water while reducing its losses to the surrounding sea.
... Finally, the Mediterranean diet group significantly increased fish intake after intervention. It is possible that this elevated fish consumption could have contributed to the lack of effect on TMAO concentration because salt-water fish produce TMAO for use in osmotic regulation 49 . This elevated fish consumption could have caused an increase in pre-formed TMAO consumption in this group, assuming that the types of fish predominantly consumed were salt-water varieties. ...
... Another area worthy of exploration is the impact of fish consumption as part of a Mediterranean diet on TMAO levels. It was not possible to study the effects of salt-water fish consumption in this study, but given that this is a potential source of pre-formed TMAO49 , it would be beneficial to investigate the effects of Mediterranean diets with and without fish on TMAO concentrations.CONCLUSIONThis study supports previous findings that serum TMAO concentrations are increased by age, metabolic syndrome risk factors and systemic exposure to lipopolysaccharide. Six months of dietary intervention with either Healthy Eating or Mediterranean goals, however, did not alter fasting TMAO concentration in a population of subjects at elevated risk for colon cancer. ...
Article
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Elevated circulating levels of trimethylamine N-oxide (TMAO) has been identified as a risk factor for numerous diseases, including cardiovascular disease (CVD) and colon cancer. TMAO is formed from trimethylamine (TMA)-precursors such as choline via the combined action of the gut microbiota and liver. We conducted a Mediterranean diet intervention that increased intakes of fiber and changed intakes of many other foods containing fat to increase the relative amount of mono-unsaturated fats in the diet. The Mediterranean diet is associated with reduced risks of chronic diseases and might counteract the pro-inflammatory effects of increased TMAO formation. Therefore, the purpose of this study was to determine if the Mediterranean diet would reduce TMAO concentrations. Fasting TMAO concentrations were measured before and after six-months of dietary intervention in 115 healthy people at increased risk for colon cancer. No significant changes in plasma TMAO or in the ratios of TMAO to precursor compounds were found in either the Mediterranean group or the comparison group that followed a Healthy Eating diet. TMAO concentrations exhibited positive correlations with age and markers of metabolic health. TMAO concentrations were not associated with circulating cytokines, but the relative abundance of Akkermansia mucinophilia in colon biopsies was modestly and inversely correlated with baseline TMAO, choline, and betaine serum concentrations. These results suggest that broad dietary pattern intervention over six months may not be sufficient for reducing TMAO concentrations in an otherwise healthy population. Disruption of the conversion of dietary TMA to TMAO should be the focus of future studies.
... Trimethylamine oxide (TMAO) is a small compound, accumulated as an osmolyte by a variety of marine organisms Bickel, 1969; see Seibel and Walsh, 2002;Yancey, 2005 for reviews). It serves an additional role as a universal protein stabilizer (Yancey and Siebenaller, 1999;Yancey et al., 2001Yancey et al., , 2004, counteracting perturbations due to salinity (Pillans et al., 2005;Hammerschlag, 2006;Deck et al., 2016), temperature (Raymond and DeVries, 1998;, hydrostatic pressure (Yancey et al., 2002;Bockus and Seibel, 2016) and urea (Somero, 1986;Baskakov et al., 1998;Yancey, 2001;Zou et al., 2002). TMAO is held at exceptionally high levels in elasmobranchs (sharks, skates and rays) that retain urea, a nitrogenous waste compound and macromolecular destabilizer, as their primary osmolyte (Smith, 1929;Forster and Goldstein, 1976;Withers, 1998;Trischitta et al., 2012). ...
... The body fluids of marine elasmobranchs are generally maintained slightly hyper-osmotic to the surrounding seawater. However, TMAO is preferentially accumulated inside the cell and contributes to a larger portion of the total osmotic pressure in the muscle and liver than it does in the plasma, which exhibits high concentrations of inorganic salts, such as Na + and Cl − (Hammerschlag, 2006). In contrast, urea readily diffuses across the cell membrane and is found at similar concentrations in both the intraand extracellular compartments. ...
... In comparison, the salinity range of bull sharks has been studied in depth because bull sharks are euryhaline and can tolerate a wide range of salinities (reviewed in Hammerschlag, 2006). Overall, bull sharks have been observed in waters from 0 -42 ppt (Snelson & Williams, 1981;Thorburn & Rowland, 2008) though specific sex and lifestage specific trends can influence habitat choice within this range. ...
... In comparison to great hammerhead and tiger sharks, the environmental tolerances of bull sharks have been very well studied because bull sharks are euryhaline and are able to survive in a wide range of salinities (Hammerschlag, 2006). Their ability to withstand a wide salinity range means that bull sharks can move into environments that are either hyper-or hyposaline to the open ocean, including estuary and mangrove habitats (e.g., Werry et al., 2012). ...
Thesis
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Aquatic highly migratory species (HMS) are economically and ecologically important, however, their highly migratory nature makes them difficult to study and thus there are knowledge gaps relating to their movement and habitat use patterns. Highly migratory sharks are likely to interact with commercial longline fishing gear and be caught as target or bycatch, which can threaten their populations. Understanding the environmental factors that influence and drive the movements of highly migratory sharks may help researchers better predict their presence and subsequently identify areas where they are vulnerability to fisheries. Here I evaluated the overlap between habitat suitability and gear restricted zones for three co-occurring apex predatory sharks in the Southwest Atlantic Ocean and Gulf of Mexico (great hammerhead Sphyrna mokarran, tiger Galeocerdo cuvier, and bull sharks Carcharhinus leucas) to identify areas in this region where these species are vulnerable to and protected from commercial longline fishing. This research was accomplished in three integrated steps. First, I reviewed and summarized what is known about the environmental drivers of great hammerhead, tiger, and bull shark habitat use and movement patterns. Second, I used the results of this review to parameterize and subsequently generate habitat suitability models for these three species. Third, I used these models to spatially compare where each species’ highly suitable habitat overlaps with longline gear restricted areas within the Southwest Atlantic Ocean and Gulf of Mexico, to identify regions where these species were both vulnerable to and protected from longline fishing gear. The results of this thesis have implications to the management of these species as well as for the conservation of other highly migratory aquatic species.
... The serum urea concentration in Blackchin Guitarfish was similar to those of marine elasmobranchs (i.e., Southern Stingray: Cain et al. 2004;Sand Tiger Carcharias taurus: Otway 2015) but was 100-fold higher than those in freshwater stingrays (Brito et al. 2015; Table S5). Serum nonprotein solids concentrations, especially urea, are significantly higher in marine elasmobranchs than in freshwater species (Hammerschlag 2006), reflecting the important osmole role of urea in marine and euryhaline elasmobranchs but not in freshwater elasmobranchs (Ballantyne and Robinson 2010). Similarly, the serum sodium and chloride concentrations herein, which were very strongly correlated, were similar to those of the Southern Stingray (Cain et al. 2004) and the Sand Tiger (Otway 2015) but were twofold higher compared to the concentrations in freshwater stingrays (Brito et al. 2015; Table S5). ...
Article
Objective The Blackchin Guitarfish Glaucostegus cemiculus is endemic to the Mediterranean Sea and is critically endangered, but relevant routine laboratory data are unavailable. Our objectives were to determine the packed cell volume (PCV), comprehensive serum chemistry analytes, and serum total thyroxine (sTT4) concentration; compare serum albumin and serum globulin concentrations as measured by two different methods; and describe the blood cell morphology of healthy, free‐ranging Blackchin Guitarfish. Methods Wild Blackchin Guitarfish were captured using a seine net. Blood samples for serum chemistry and hematological analyses were obtained and measured using routine laboratory methods. The fish were tagged and released. Result This study included 43 Blackchin Guitarfish (17 males and 26 females) that were younger than 6 months as estimated based on total length and body weight. The median PCV ( n = 23) was 22% (minimum–maximum [min–max] = 15–25%). Median sTT4 ( n = 10) measured by chemiluminescence immunoassay was 7.86 nmol/L (min–max = 7.52–9.57 nmol/L). The study included a comprehensive, 25‐analyte serum chemistry analysis (e.g., serum iron and unbound and total iron‐binding capacity) and a morphological description of all blood cells. Serum electrophoresis (SEP; n = 13) yielded a consistent serum albumin‐migrating protein fraction and four globulin fractions. Serum electrophoretograms corroborating these results are presented. Conclusion In Blackchin Guitarfish, the serum albumin‐migrating fraction measured by SEP combined with serum total protein concentration yields a much higher albumin concentration compared to that measured by bromocresol green spectrophotometry. The true identity of this albumin‐migrating fraction remains to be identified. The analytes' calculated 2.5–97.5% interpercentile intervals should be considered as reference intervals applying to Blackchin Guitarfish of similar age but should be applied cautiously to adult fish.
... Estas premisas explicarían los niveles obtenidos para ambos minerales en P. glauca. Las concentraciones obtenidas de Na y K no expresan ningún impacto nutricional; sin embargo, la presencia de estos elementos monovalentes (Na y K) como divalentes (Mg y Ca) en los fluidos corporales de los elasmobranquios, es indicador que están regulados en concentraciones por debajo del nivel del agua de mar (Hammerschlag, 2006). La media estimada para el P mostró valores muy inferiores ante lo presentado por las especies amazónicas y marinas comerciales, mientras que el Fe mostró en su mayoría una distribución por debajo de las concentraciones promedio de las especies comparadas. ...
Article
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The aim of this study was to evaluate the biological, physicochemical and technological related characteristics of the blue shark Prionace glauca. The sample included 128 specimens to determine their biological and technological properties and 27 specimens for their physicochemical characteristics. Biometric data of length and weight(142 to 281 cm and 10.5 to 93.0 kg for males; 153.5 to 255.0 cm and 14.5 to 80.0 kg for females), allometry index (males 3.27 and females 2.87), technological potential through different types of performance (RED: 83.9±0.03%, RESV: 67.2±0.04%, RSCV: 48.9±0.07%and RPC: 33.5±0.07%) and water retention capacity in the muscle (16.1±0.03%). With in the physicochemical characteristics, the proximal chemical composition was analysed(protein 21.8±0.23; fat 0.6±0.03; humidity 78.0±0.31; ash 1.3±0.01) and mineral composition(Cu: 2.0±0.11 mg/kg; Fe: 17.8±1.95 mg/kg; Zn: 25.8±1.76 mg/kg; Ca: 4.3±0.27 mg/100 g;Mg: 95.4±7.87 mg/100 g; Na: 716.3±24.03 mg/100 g; K: 1526.1±54.4 mg/100 g; P: 439.5±15.76mg/100 g). There was no evidence of significant differences based on sex
... In marine fishes, it is increasingly documented that large effective population sizes and wide distributions over diverse environments favor the effects of natural selection and minimize the random effect of genetic drift despite the homogenizing effect of gene flow Conover et al., 2006;Diopere et al., 2018 (Gervais et al., 2018;Santos et al., 2021;Wheeler et al., 2021) and it is the environmental factor most regularly associated with distribution and migration patterns of elasmobranchs (da Silva et al., 2022;Kajiura & Tellman, 2016;Osgood et al., 2021). Similarly, salinity gradients are known to affect habitat suitability and movement in elasmobranchs (Heupel & Simpfendorfer, 2008;Lauria et al., 2015), as well as behaviour and physiology (Dowd et al., 2010;Hammerschlag, 2006;Schlaff et al., 2014). The role of chlorophyll as driver of adaptive divergence is more difficult to ascertain. ...
Article
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Adaptive divergence in response to environmental clines are expected to be common in species occupying heterogeneous environments. Despite numerous advances in techniques appropriate for non‐model species, gene–environment association studies in elasmobranchs are still scarce. The bronze whaler or copper shark (Carcharhinus brachyurus) is a large coastal shark with a wide distribution and one of the most exploited elasmobranchs in southern Africa. Here, we assessed the distribution of neutral and adaptive genomic diversity in C. brachyurus across a highly heterogeneous environment in southern Africa based on genome‐wide SNPs obtained through a restriction site‐associated DNA method (3RAD). A combination of differentiation‐based genome‐scan (outflank) and genotype–environment analyses (redundancy analysis, latent factor mixed models) identified a total of 234 differentiation‐based outlier and candidate SNPs associated with bioclimatic variables. Analysis of 26,299 putatively neutral SNPs revealed moderate and evenly distributed levels of genomic diversity across sites from the east coast of South Africa to Angola. Multivariate and clustering analyses demonstrated a high degree of gene flow with no significant population structuring among or within ocean basins. In contrast, the putatively adaptive SNPs demonstrated the presence of two clusters and deep divergence between Angola and all other individuals from Namibia and South Africa. These results provide evidence for adaptive divergence in response to a heterogeneous seascape in a large, mobile shark despite high levels of gene flow. These results are expected to inform management strategies and policy at the national and regional level for conservation of C. brachyurus populations.
... Whaler shark attacks were found to increase closer to a river, with 47% of attacks occurring within 100 m of a river mouth. This coincides with the preferred habitat zone for bull sharks, i.e. coastal zones with high freshwater inflow (Carlson et al. 2010), as they can osmoregulate in both salt and fresh water (Pillans & Franklin 2004, Hammerschlag 2006. Acoustically tagged young bull sharks spend most of their time within 11 km of the river mouth (Heupel & Simpfendorfer 2008), and bull sharks breed and feed in nearshore coastal areas and rivers (Carlson et al. 2010, Werry et al. 2011. ...
Thesis
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Shark attacks are rare but traumatic events that generate social and economic costs and often lead to calls for enhanced attack mitigation strategies that are detrimental to sharks and other wildlife. Improved understanding of the influence of environmental conditions on shark attack risk may help to inform shark management strategies. Here, we developed predictive models for the risk of attack by white Carcharodon carcharias, tiger Galeocerdo cuvier, and bull/whaler Carcharhinus spp. sharks in Australian waters based on location, sea surface temperature (SST), rainfall, and distance to river mouth. A generalised additive model analysis was performed using shark attack data and randomly generated pseudo-absence non-attack data. White shark attack risk was significantly higher in warmer SSTs, increased closer to a river mouth (<10 km), and peaked at a mean monthly rainfall of 100 mm. Whaler shark attack risk increased significantly within 1 km of a river mouth and peaked in the summer months. Tiger shark attack risk increased significantly with rainfall. We performed additional temporal and spatio-temporal analyses to test the hypothesis that SST anomaly (SSTanom) influences white shark attack risk, and found that attacks tend to occur at locations where there is a lower SSTanom (i.e. the water is relatively cooler) compared to surrounding areas. On the far north coast of eastern Australia—an attack hotspot—a strengthening of the East Australian Current may cause white sharks to move into cooler upwelling waters close to this stretch of the coast and increase the risk of an attack.
... Dicho proceso es similar en la urea, que es un producto de excreción del proceso metabólico retenido en los tejidos de los elasmobranquios, utilizado para su osmorregulación (Fisk et al., 2002). Se ha identificado que la urea está agotada en 15 N, que disminuye los valores del δ 15 N, generando una subestimación en el nivel trófico de los elasmobranquios (Hammerschlag, 2006). ...
Thesis
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Los estudios sobre interacciones tróficas han sido fundamentales para comprender la coexistencia entre especies dentro de una comunidad. Por esta razón, la presente investigación tiene como objetivo identificar las posibles estrategias alimenticias que facilitan la coexistencia entre las rayas Hypanus dipterurus, Narcine entemedor y Rhinoptera steindachneri, a partir de estudios de contenidos estomacales previamente realizados y análisis de isótopos estables δ13C y δ15N en Bahía de La Paz (2013-2017). Se detectó diferencias entre los principales grupos de presas consumidos por estos depredadores, dominando los sipuncúlidos en N. entemedor (%PSIRI=52), los bivalvos en H. dipterurus (%PSIRI=45) y los misidáceos en R. steindachneri (%PSIRI=78). No se evidenció sobreposición trófica interespecífica en ninguno de los factores evaluados (temporadas, sexos, estados de madurez sexual y grupos de edades), en donde los grupos alimenticios ya descritos son los responsables de la disimilitud trófica. La composición isotópica mostró que H. dipterurus es una especie generalista de niveles tróficos que varían con la ontogenia y con el uso de hábitat más extenso en la zona. Contrario a N. entemedor, que es un depredador especialista de sipuncúlidos y poliquetos, y con un estrecho uso de hábitat, mientras que R. steindachneri es un depredador especialista probablemente de presas de bajo nivel trófico (pequeños crustáceos malacostráceos), con movimientos entre zonas costeras y oceánicas. El acceso diferencial a los grupos de presas, la especialización trófica y el uso preferencial por diversas zonas de alimentación fueron las principales estrategias usadas por los batoideos para facilitar la coexistencia en la zona.
... comm.). However, chondrichthyan blood salinity is 35-37 ppt so decreasing salinity is not advised (Hammerschlag 2006). ...
... Osmolarity is of primary importance for all sperm holding media, with inappropriate media resulting in hypoosmotic membrane swelling, or hyperosmotic crenation, of sperm cells. For sharks, it is expected that seminal fluids would have a similar osmolarity as serum and the surrounding environment, and therefore, isotonic solutions with osmolarities between 800 and 1000 mOsm would be better suited for liquid storage of sperm [39,[52][53][54]. We clearly saw negative effects of hypoosmotic stress as indicated by significantly decreased normal morphology with decreased tonicity of the media. ...
Article
abstract: Three experiments were performed to evaluate the effects of osmolarity, temperature, media and cryoprotectants on white spotted bamboo shark (Chiloscyllium plagiosum) spermatozoa. Semen was collected from 7 different males using a massage technique with the animals held in tonic immobilization with gills submerged. A Computer Assisted Sperm Analysis (CASA) system was used to assess sperm motility. Experiment one evaluated the effects of Hank’s balanced salt solution (HBSS) with different osmolarities (200, 400, 800 and 1000 mOsm Kg1) and incubation temperatures (5 °C and 24 °C [room temperature]) over time (6 h, 12 h and 24 h). Membrane integrity and morphology were degraded (P 0.05) sperm parameters were observed with HBSS 1000 and HBSS 800, respectively. In addition, TM, VAP, and curvilinear velocity (VCL) were all reduced (P
... Approximately 50% of osmotic pressure on blood cells and tissues is induced by the salt content. In blood of sharks, accumulation of significant amount of urea and trimethylamine oxide, diffusing poorly through the cells of kidneys and gills, which increases the osmotic pressure, is observed, (Hammerschlag, 2006). ...
Article
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The results of hematological, cytochemical, and biochemical surveys for fish blood in the specimen Ocellate river stingray Potamotrygon motoro and two specimens of cat sharks including the Halmahera epau-lette shark Hemiscyllium halmahera and the grey bambooshark Chiloscyllium griseumare have been reported. A comparison in the parameters analyzed in the survey between the common carp Cyprinus carpio, the wels catfish Silurus glanis, and the sterlet Acipenser ruthenus has been performed. A high percentage of eosinophils involved in antiparasite immunity in the Cartilaginous fishes is recorded. A high content of cationic protein in lysosomes of neutrophils in these fish species can indicate a considerable potent phagocytic activity of the latter. A low amount of alanine aminotransferase in the analyzed shark and ray specimens compared to the bony fish was recorded, which indicate the strength of membranes in hepatocytes and cardiomyocytes.
... Marine and euryhaline elasmobranchs in SW regulate urea and other body fluid solutes [trimethylamine oxide (TMAO), Na + , Cl − ] such that they remain iso-or slightly hyperosmotic to their environment (Hammerschlag, 2006). While little information is available, it seems that the thyroid axis may contribute to elasmobranch osmoregulation. ...
Thesis
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This thesis aimed to understand the role that the hypothalamus-pituitary-thyroid (HPT) axis plays in appetite regulation of goldfish (Carassius auratus). I altered nutritional and thyroid statuses to measure the response of thyroid axis components and appetite-regulating peptides. I predicted that fasting would downregulate the thyroid axis and trigger an orexigenic response, while overfeeding would upregulate the thyroid axis and trigger an anorexigenic response. Additionally, I predicted that hyperthyroid conditions would lead to negative feedback of the thyroid axis and an orexigenic response, whilst opposite under hypothyroid conditions. I uncovered for both experiments that the thyroid axis in goldish is most responsive to overfeeding and hyperthyroidism. Overfeeding led to a time-dependent increase in central thyroid transcripts while fasting decreased thyroid hormone degradation peripherally with no central response, no treatment altered levels of thyroid hormone in circulation. Hyperthyroidism resulted in negative feedback to the pituitary, but not hypothalamus, and did not lead to an increase in food intake despite an increase in the levels of thyroxine. The thyroid inhibitor, propylthiouracil, did not induce hypothyroidism or alter the expression of any thyroid axis transcript. Appetite-regulating peptides correlated weakly to changes in the thyroid, suggesting an overall poor association in goldfish between appetite regulation and thyroid status.
... Ni is moderately toxic to aquatic organisms, and exerts its toxicity through different cellular pathways, mainly disruption of essential metal homeostasis (e.g., Ca, Mg, and Fe) and the generation of Reactive Oxygen Species (ROS) (Brix et al., 2017), similarly noted for V, also a redoxactive metal. Vanadium contamination, in particular, may be of significant concern in elasmobranchs, as the main excretion route for this element is urine, and elasmobranch osmoregulation is carried out by increasing or decreasing blood urea concentrations (Hammerschlag, 2006). No toxicity thresholds or detoxification mechanisms have been established for these elements in elasmobranchs. ...
Article
This study comprises a novel report on subcellular metal partitioning and metallothionein (MT) metal detoxification efforts in lesser numbfish (Narcine brasiliensis) electric ray specimens, as well as the first assessment on MT contents in any ray electric organ. Individuals sampled from an area in Southeastern Brazil affected by the Mariana dam rupture disaster were assessed concerning subcellular metal partitioning and MT metal-detoxification in the liver, gonads, electric organ and muscle of both adults and embryos. Yolk was also assessed when available. Relative total and heat-stable (bioavailable) metal and metalloid comparisons between adults and embryos in different developmental stages demonstrates maternal transfer of both total and bioavailable metals and significant MT associations demonstrate the detoxification of As, Ag, Mn, Ni, Cd, Co, Cu, Se and V through this biochemical pathway. Our findings expand the lacking ecotoxicological assessments for this near-threatened species and indicates significant ecological concerns, warranting further biomonitoring efforts.
... In large rivers, C. leucas is able to cover distances of many thousands of kilometers upriver, due to urea-based osmoregulation (PanG et al. 1977;hazon et al. 2003;anderson et al. 2005a;hammerschlaG 2006;trischitta et al. 2012). This large-scale freshwater migration leads to extended periods in freshwater during the early stages of the natural life cycle of C. leucas (see Table 11). ...
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The bull shark (Carcharhinus leucas Valenciennes, 1839) is a large, primarily coastally distributed shark famous for its ability to penetrate far into freshwater bodies in tropical, subtropical, and warm-temperate climates. It is a cosmopolitan species with a geographical range that includes the coastlines of all major ocean basins (Atlantic Ocean, Indian Ocean, Pacific Ocean). As a consequence, freshwater occurrences of C. leucas are possible everywhere inside its geographic range. Carcharhinus leucas is a fully euryhaline, amphidromous species and possibly the widest-ranging of all freshwater tolerating elasmobranchs. This species is found not only in river systems with sea access that are not interrupted by human impediments but in hypersaline lakes as well. Rivers and estuaries are believed to be important nursery grounds for C. leucas, as suggested by observations of pregnant females in estuaries and neonates with umbilical scars in rivers and river mouths. Due to the physical capability of this species to enter riverine systems, the documentation of its occurrence in fresh and brackish water is essential for future conservation plans, fishery inspections, and scientific studies that focus on the link between low salinity habitats, shark nurseries, and feeding areas. The author’s review of the available literature on C. leucas revealed the absence of a comprehensive overview of fresh and brackish water localities (rivers and associated lakes, estuaries) with C. leucas records. The purpose of this literature review is to provide a global list of rivers, river systems, lakes, estuaries, and lagoons with records and reports of this species, including a link to the used references as a base for regional, national, and international conservation strategies. Therefore, the objective of this work is to present lists of fresh and brackish water habitats with records of C. leucas as the result of an extensive literature review and analysis of databases. This survey also took into account estuaries and lagoons, regarding their function as important nursery grounds for C. leucas. The analysis of references included is not only from the scientific literature, but also includes semi-scientific references and the common press if reliable. The result of 415 global fresh and brackish water localities with evidence of C. leucas highlights the importance of these habitats for the reproduction of this species. Moreover, gaps in available distribution maps are critically discussed as well as interpretations and conclusions made regarding possible reasons for the distribution range of C. leucas, which can be interpreted as the result of geographic circumstances, but also as a result of the current state of knowledge about the distribution of this species. The results of the examination of available references were used to build a reliable and updated distribution map for C. leucas, which is also presented here.
... Lower osmolality was probably caused by concomitant lower urea levels, given the relevance of this osmolyte in elasmobranchs (Ballantyne & Robinson, 2010). Furthermore, given that urea is regulated by the kidneys (Hammerschlag, 2006), it is possible that the stress experienced by Shortnose guitarfish individuals harmed their capacity to ensure urea retention. This effect reflects osmoregulatory dynamics during stressful situations. ...
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The assessment of physiological responses to capture provides useful information for elasmobranch conservation. In particular, understanding these impacts in species caught as bycatch that are released after capture can predict their “post‐release” fate and aid in management plans. Although well studied in several species, capture‐stress is nonetheless frequently assessed without considering putative variability between sexes. Given the high mortality of pregnant Zapteryx brevirostris females reported in the literature, the present study aimed at determining greatest vulnerability period for males. Our results demonstrate that, when caught during the reproductive period, males display higher mortality (68%) than when caught outside the reproductive period (zero mortality). Seven out of 11 markers (i.e. sodium, chloride, potassium, lactate, phosphorus, triglycerides and condition factor) differed significantly following capture‐induced stress between males caught during the reproductive period and those caught outside this period. Results demonstrate the need for specific protocols during the reproductive period, also considering the influence of sex on physiological responses to stress for effective management.
... Some studies also report that excess exposure to this element causes cardiovascular alterations [72]. Interestingly, the main excretion route for this element is urine, which may of significance to elasmobranch health, as osmo-regulation in this group is performed by increasing or decreasing blood urea concentrations [73]. Again, not many studies are available concerning this element in elasmobranchs. ...
Article
Background Elasmobranchs are particularly vulnerable to environmental metal contamination, accumulating these contaminants at high rates and excreting them slowly. The blue shark Prionace glauca L. is one of the most heavily fished elasmobranchs, although information regarding metal contamination and detoxification in this species is notably lacking. Methods Blue sharks were sampled in the western North Atlantic Ocean, in offshore waters adjacent to Cape Cod, Massachusetts. Total liver and muscle metal concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS), metallothionein detoxification and oxidative stress endpoints were determined by UV-Vis spectrophotometry. Results Metallothionein detoxification occurred for As, Cd, Cs, Cu, Hg, Pb, Se, Ti and Zn in liver, and for As, Cd, Cs, Pb, Se, and Zn in muscle, while reduced glutathione defenses seem to be related to Co and Zn exposure. Conclusion This is the first report for several metals (Ag, Co, non-radioactive Cs, Sb, Ti and V) for this species, which will aid in establishing baseline elemental data for biomonitoring efforts, health metrics, and conservation measures.
... Elasmobranch liver is a highly complex tissue due to its role in osmotic regulation and energy storage (Hamlett, 1999;Hoffmayer et al., 2006). The synthesis of urea (CO(NH 2 ) 2 ) and the presence of trimethylamine n-oxide (TMAO, C 3 H 9 NO; to counteract the fact that urea inhibits protein binding and folding; Yancey, 2005) is key to maintain osmotic balance (Hazon et al., 2003;Hammerschlag, 2006). Acclimatization to reduced salinity environments by lemon sharks (Negaprion brevirostris), for example, results in increased urea and extracellular solute (e.g., TMAO) excretion (Goldstein et al., 1968). ...
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Stable‐isotope analysis (SIA) provides a valuable tool to address complex questions pertaining to elasmobranch ecology. Liver, a metabolically active, high turnover tissue (~166 days for 95% turnover), has the potential to reveal novel insights into recent feeding/movement behaviours of this diverse group. To date, limited work has used this tissue, but ecological application of SIA in liver requires consideration of tissue preparation techniques given the potential for high concentrations of urea and lipid that could bias δ¹³C and δ¹⁵N values (i.e., result in artificially lower δ¹³C and δ¹⁵N values). Here we investigated the effectiveness of (a) deionized water washing (WW) for urea removal from liver tissue and (b) chloroform‐methanol for extraction of lipids from this lipid rich tissue. We then (a) established C:N thresholds for deriving ecologically relevant liver isotopic values given complications of removing all lipid and (b) undertook a preliminary comparison of δ¹³C values between tissue pairs (muscle and liver) to test if observed isotopic differences correlated with known movement behaviour. Tests were conducted on four large shark species: the dusky (DUS, Carcharhinus obscurus), sand tiger (RAG, Carcharias taurus), scalloped hammerhead (SCA, Sphyrna lewini) and white shark (GRE, Carcharodon carcharias). There was no significant difference in δ¹⁵N values between lipid‐extracted (LE) liver and lipid‐extracted/water washed (WW) treatments, however, WW resulted in significant increases in %N, δ¹³C and %C. Following lipid extraction (repeated three times), some samples were still biased by lipids. Our species‐specific “C:N thresholds” provide a method to derive ecologically viable isotope data given the complexities of this lipid rich tissue (C:N thresholds of 4.0, 3.6, 4.7 and 3.9 for DUS, RAG, SCA and GRE liverLEWW tissue, respectively). The preliminary comparison of C:N threshold corrected liver and muscle δ¹³C values corresponded with movement/habitat behaviours for each shark; minor differences in δ¹³C values were observed for known regional movements of DUS and RAG (δ¹³CDiffs = 0.24 ± 0.99‰ and 0.57 ± 0.38‰, respectively), while SCA and GRE showed greater differences (1.24 ± 0.63‰ and 1.08 ± 0.71‰, respectively) correlated to large‐scale movements between temperate/tropical and pelagic/coastal environments. These data provide an approach for the successful application of liver δ¹³C and δ¹⁵N values to examine elasmobranch ecology.
... Marine and euryhaline elasmobranchs in SW regulate urea and other body fluid solutes [trimethylamine oxide (TMAO), Na + , Cl − ] such that they remain iso-or slightly hyperosmotic to their environment (302). While little information is available, it seems that the thyroid axis may contribute to elasmobranch osmoregulation. ...
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In all vertebrates, the thyroid axis is an endocrine feedback system that affects growth, differentiation, and reproduction, by sensing and translating central and peripheral signals to maintain homeostasis and a proper thyroidal set-point. Fish, the most diverse group of vertebrates, rely on this system for somatic growth, metamorphosis, reproductive events, and the ability to tolerate changing environments. The vast majority of the research on the thyroid axis pertains to mammals, in particular rodents, and although some progress has been made to understand the role of this endocrine axis in non-mammalian vertebrates, including amphibians and teleost fish, major gaps in our knowledge remain regarding other groups, such as elasmobranchs and cyclostomes. In this review, we discuss the roles of the thyroid axis in fish and its contributions to growth and development, metamorphosis, reproduction, osmoregulation, as well as feeding and nutrient metabolism. We also discuss how thyroid hormones have been/can be used in aquaculture, and potential threats to the thyroid system in this regard.
... Similarly, fossil coelacanth specimens were found in freshwater sediments (15), although extant coelacanths live in marine environments. Extant marine elasmobranchs (sharks and rays), holocephalan fishes (e.g., the elephant shark), as well as L. chalumnae are ureosmotic regulators (36,40,44). They are ionic regulators that maintain concentrations of ions in the extracellular fluid (including sodium and chloride) below levels found in seawater, while osmolarity is adjusted to match or slightly exceed seawater levels by accumulation of osmolytes such as urea and trimethylamine N-oxide (TMAO). ...
Article
The conquest of freshwater and terrestrial habitats was a key event during vertebrate evolution. Occupation of low-salinity and dry environments required significant osmoregulatory adaptations enabling stable ion and water homeostasis. Sodium is one of the most important ions within the extracellular liquid of vertebrates and molecular machinery for urinary reabsorption of this electrolyte is critical for the maintenance of body osmoregulation. Key ion channels involved in the fine-tuning of sodium homeostasis in tetrapod vertebrates are epithelial sodium channels (ENaC) which allow the selective influx of sodium ions across the apical membrane of epithelial cells lining the distal nephron or the colon. Furthermore, ENaC-mediated sodium absorption across tetrapod lung epithelia is crucial for the control of liquid volumes lining the pulmonary surfaces. ENaCs are vertebrate-specific members of the degenerin/ENaC family of cation channels, however, there is limited knowledge in the evolution of ENaC within this ion channel family. This review outlines current concepts and hypotheses on ENaC phylogeny and discusses the emergence of regulation-defining sequence motifs in the context of osmoregulatory adaptations during tetrapod terrestrialisation. Based on the distinct regulation and expression of ENaC isoforms in tetrapod vertebrates we discuss the potential significance of ENaC orthologs in osmoregulation of fish as well as the putative fates of atypical channel isoforms in mammals. We hypothesize that ancestral proton-sensitive ENaC orthologs might have aided the osmoregulatory adaptation to freshwater environments whereas channel regulation by proteases evolved as a molecular adaptation to lung liquid homeostasis in terrestrial tetrapods.
... We hypothesised that chl-a and SST would influence shark occurrence and expected to find pelagic sharks offshore in less turbid waters. We also hypothesised salinity would limit these species to higher and more stable salinities offshore (Hammerschlag, 2006;Bernal et al., 2012) due to the high cost of osmoregulation (Pang et al., 1977), and that geophysical and geomorphological parameters would influence shark occurrence in different locations rather than sediment characteristics. ...
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Many of the world’s shark populations are in decline, indicating the need for improved conservation and management. Well managed and appropriately located marine parks and marine protected areas (MPAs) have potential to enhance shark conservation by restricting fisheries and protecting suitable habitat for threatened shark populations. Here, we used shark occurrence records collected by commercial fisheries to determine suitable habitat for pelagic sharks within the Australian continental Exclusive Economic Zone (EEZ), and to quantify the amount of suitable habitat contained within existing MPAs. We developed generalised linear models using proportional occurrences of pelagic sharks for three families: Alopiidae (thresher), Carcharhinidae (requiem), and Lamnidae (mackerel) sharks. We also considered aggregated species from the Lamnidae and Carcharhinidae families (‘combined sharks’ in the models). Using a set of environmental predictors known to affect shark occurrence, including chlorophyll-a concentration, salinity, sea surface temperature, and turbidity, as well as geomorphological, geophysical, and sedimentary parameters, we found that models including sea surface temperature and turbidity were ranked highest in their ability to predict shark distributions. We used these results to predict geographic regions where habitat was most suitable for pelagic sharks within the Australian EEZ, and our results revealed that suitable habitat was limited in no-take zones within MPAs. For all shark groupings, suitable habitats were found mostly at locations exposed to fishing pressure, potentially increasing the vulnerability of the pelagic shark species considered. Our predictive models provide a foundation for future spatial planning and shark management, suggesting that strong fisheries management in addition to MPAs is necessary for pelagic shark conservation.
... The unique physiology of elasmobranchs leads to additional challenges in interpreting stable isotope values due to the retention of urea in body tissues for osmoregulatory purposes ( Hazon et al. 2003;Hammerschlag 2006). Urea is enriched in 14 N relative to pure protein due to lighter isotopes reacting faster and being preferentially selected during amination processes ( Gannes et al. 1998). ...
Article
The presence of lipids and urea in elasmobranch tissues can affect carbon (δ13C) and nitrogen (δ15N) stable isotope values, introducing bias in food web interpretations. Information on how lipids and urea affect δ13C/δ15N is only available for < 5% of ~ 1150 described elasmobranch species and results are highly variable among existing studies. Here, we investigate the effects of lipid and urea extraction on δ13C, δ15N, and C:N ratios in muscle and blood plasma of two batoids (Pastinachus ater and Himantura australis) and examine the influence of lipid/urea extraction on isotopic niche size and overlap. Lipid extraction (LE) did not affect δ13C, δ15N, or C:N ratios, suggesting low lipid content. Urea extraction (UE), however, increased δ15N and C:N in muscle. The ~ 1‰ δ15N increase represents a shift of ~ 0.5 trophic levels relative to bulk samples, highlighting the importance of UE to accurately assess trophic positions. Although there was no effect of any treatment on niche size, the probability of P. ater occurring within the niche of H. australis increased following UE. Overall, results suggest that urea should be removed from muscle prior to analysis, but LE is not required. Given the interspecific variability in the effects of lipid/urea on elasmobranch δ13C/δ15N, more studies are needed to assess the effects of lipid and urea on a broader range of species to produce a generalized understanding. Where no species‐specific data are available, we recommend pilot samples are analyzed to determine if LE is needed prior to preparation of the overall sample set.
... Whaler shark attacks were found to increase closer to a river, with 47% of attacks occurring within 100 m of a river mouth. This coincides with the preferred habitat zone for bull sharks, i.e. coastal zones with high freshwater inflow (Carlson et al. 2010), as they can osmoregulate in both salt and fresh water (Pillans & Franklin 2004, Hammerschlag 2006. Acoustically tagged young bull sharks spend most of their time within 11 km of the river mouth (Heupel & Simpfendorfer 2008), and bull sharks breed and feed in nearshore coastal areas and rivers (Carlson et al. 2010, Werry et al. 2011. ...
Article
Shark attacks are rare but traumatic events that generate social and economic costs and often lead to calls for enhanced attack mitigation strategies that are detrimental to sharks and other wildlife. Improved understanding of the influence of environmental conditions on shark attack risk may help to inform shark management strategies. Here, we developed predictive models for the risk of attack by white Carcharodon carcharias, tiger Galeocerdo cuvier, and bull/ whaler Carcharhinus spp. sharks in Australian waters based on location, sea surface temperature (SST), rainfall, and distance to river mouth. A generalised additive model analysis was performed using shark attack data and randomly generated pseudo-absence non-attack data. White shark attack risk was significantly higher in warmer SSTs, increased closer to a river mouth (<10 km), and peaked at a mean monthly rainfall of 100 mm. Whaler shark attack risk increased significantly within 1 km of a river mouth and peaked in the summer months. Tiger shark attack risk increased significantly with rainfall. We performed additional temporal and spatio-temporal analyses to test the hypothesis that SST anomaly (SSTanom) influences white shark attack risk, and found that attacks tend to occur at locations where there is a lower SSTanom (i.e. the water is relatively cooler) compared to surrounding areas. On the far north coast of eastern Australia — an attack hotspot — a strengthening of the East Australian Current may cause white sharks to move into cooler upwelling waters close to this stretch of the coast and increase the risk of an attack.
... Seawater is a sodium chloride solution containing sulphates and bicarbonates of K + , Ca 2+ and Mg 2+ . Aquatic organisms have specific total dissolved solids (TDS) concentration, ranges within which a tolerable internal osmotic pressure can be maintained through osmoregulation [6,11,12]. ...
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A few major ions contribute most of the weight of dissolved solids in water. Direct determination of total dissolved solids (TDS) concentration is tedious, and the electrical conductivity of freshwater and the salinity of saline water are common surrogates for TDS in aquaculture. The primary concern over dissolved solids is maintaining TDS concentration within a range that allows effective osmoregulation by culture species. There is usually more concern over TDS concentration in inland, saline water or brackishwater aquaculture than in freshwater aquaculture. The handheld salinity refractometer is used almost exclusively to measure the salinity of saline waters for aquaculture. Suspended solids comprise mineral soil particles, living microorganisms (especially phytoplankton) and decaying organic matter cause turbidity, and amount of suspended solids is usually assessed from water clarity as determined with a Secchi disk. Turbidity limits light penetration and restricts the depth to which photosynthesis may occur. Turbidity from suspended soil particles usually is a negative factor while plankton turbidity normally is a positive factor in fertilized ponds. Nevertheless, in fertilized ponds or un-aerated ponds with feeding, excessive plankton turbidity causes low nighttime dissolved oxygen concentrations. Turbidity from suspended soil particles may be beneficial by reducing light penetration for phytoplankton growth in mechanically-aerated ponds with feeding, but soil particles suspended by aeration settle creating zones of organically-enriched sediment. Such sediment may result in anaerobic areas from which microbial respiration releases toxic metabolites. Methods of managing dissolved and suspended solids and sediment are summarized.
... Following defatting, all elasmobranch muscle samples were rinsed in distilled water three times to remove urea [72]. This compound is found at high concentrations in marine elasmobranch tissues [97,98], and may lower apparent 15 N/ 14 N ratios of muscle tissue [99,100]. ...
Article
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An extensive ecological literature applies stable isotope mixing models to derive quantitative dietary reconstructions from isotope ratios of consumer tissues. While this approach works well for some organisms, it is challenging for consumers with complex, varied diets, including humans; indeed, many archaeologists have avoided the use of mixing models because uncertainties in model outputs are sufficiently large that the findings are not helpful in understanding ancient lifeways. Here, we exploit an unparalleled opportunity to evaluate the feasibility of dietary quantification in a nutritionally and isotopically complex context on the Cape Peninsula, South Africa. Delta values (δ¹³C and δ¹⁵N) of 213 indigenous food samples enable us to characterise four food groups: terrestrial plants, terrestrial vertebrates, marine invertebrates and marine vertebrates. A recent study of baboons that consumed marine and terrestrial foods provides insight into the relationship between such foods and consumer tissue isotopes. We use this information to refine our interpretation of δ¹⁵N and especially δ¹³C in bone collagen from 35 archaeological hunter-gatherers, achieving better estimates of the relative importance of marine and terrestrial foods in the diet than has hitherto been possible. Based on Bayesian stable isotope mixing model (SIMM) outputs, we infer that the trophic enrichment factor (TEF) for δ¹³Cbone collagen in these coastal humans is closer to +3 than +5‰. In the most ¹³C- and ¹⁵N-rich individuals, 65–98% of bone collagen (95% credible intervals) derived from marine foods. Conversely, in ¹³C and ¹⁵N-poor individuals, 7–44% of bone collagen derived from marine foods. The uncertainties discussed here highlight the need for caution when implementing SIMMs in studies of consumers with complex diets. To our knowledge, this work constitutes the most detailed and most tightly constrained study of this problem to date.
... The blood of elasmobranchs (sharks, skates, and rays) and of non-cartilaginous fishes represent highly divergent food sourceselasmobranch blood often contains 2 to 3 orders of magnitude more urea than that of non-cartilaginous fishes (Wells et al., 1986;Hammerschlag, 2006). Nonetheless, these strongly denaturing conditions (Zou et al., 1998;Bennion and Daggett, 2003) seem to present no impediment to those piscicolid species that effectively parasitize elasmobranchs. ...
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Leeches (Annelida: Hirudinea) possess powerful salivary anticoagulants and, accordingly, are frequently employed in modern, authoritative medicine. Members of the almost exclusively marine family Piscicolidae account for 20% of leech species diversity, and feed on host groups (e.g., sharks) not encountered by their freshwater and terrestrial counterparts. Moreover, some species of Ozobranchidae feed on endangered marine turtles and have been implicated as potential vectors for the tumor-associated turtle herpesvirus. In spite of their ecological importance and unique host associations, there is a distinct paucity of data regarding the salivary transcriptomes of either of these families. Using next generation sequencing, we profiled transcribed, putative anticoagulants and other salivary bioactive compounds that have previously been linked to bloodfeeding from 7 piscicolid species (3 elasmobranch-feeders; 4 non-cartilaginous fish-feeders) and 1 ozobranchid species (2 samples). In total, 149 putative anticoagulants and bioactive loci were discovered in varying constellations throughout the different samples. The putative anticoagulants showed a broad spectrum of described antagonistic pathways, such as inhibition of factor Xa and platelet aggregation, that likely have similar bioactive roles in marine fish and turtles. A transcript with homology to ohanin, originally isolated from king cobras, was found in Cystobranchus vividus but is otherwise unknown from leeches. Estimation of selection pressures for the putative anticoagulants recovered evidence for both positive and purifying selection along several isolated branches in the gene trees and positive selection was also estimated for a few select codons in a variety of marine species. Similarly, phylogenetic analyses of the amino acid sequences for several anticoagulants indicated divergent evolution.
Article
Thromboelastography (TEG) is a hemostatic assay evaluating clot initiation time, kinetics, strength, and extent of fibrinolysis. Hemostatic assays in nonmammalian species have been less extensively studied because of lack of taxon-specific reagents and unique physiology. Hemostatic or hemorrhagic disease has been described postmortem in elasmobranchs, but antemortem detection of coagulopathies is limited in this taxon. The study aimed to establish an elasmobranch TEG protocol to improve hemostatic evaluation and facilitate advanced treatment options for animals under human care. Multiple clotting initiators were assessed for efficacy with frozen-thawed citrated plasma, fresh citrated plasma, and fresh whole citrated blood: RapidTEGTM, citrated kaolin, Reptilase®, and species brain-derived thromboplastin prepared by two different methods. Initial evaluation found plasma samples clot inconsistently, but TEG analyses using fresh whole blood consistently led to measurable TEG reactions using multiple clotting initiators. The most reliable elasmobranch TEG results were observed using citrated fresh whole blood and the RapidTEG clot initiation reagent.
Article
Objective Two Cownose Rays Rhinoptera bonasus were presented for management of a severe capsalid monogenean infection Benedeniella posterocolpa in a mixed species habitat at an aquarium. Methods A series of freshwater (FW) dips were elected to mitigate parasite resistance to praziquantel due to the endemic monogenean population in the system. A pretreatment blood sample was opportunistically obtained, and subsequent samples were processed due to development of clinical signs. Result While the first FW dip was tolerated well and did not induce abnormal behavior, the second led to one individual presenting with tachypnea, pallor, and lethargy. Marked hematological abnormalities requiring medical intervention occurred in both individuals after the second dip. After treatment with elasmobranch Ringer's fluid therapy, sodium bicarbonate, prednisolone acetate, and vitamin E/selenium in the more severely affected ray, and elasmobranch Ringer's alone in the second ray, hematologic derangements and symptoms resolved. Hemoconcentration, hyperproteinemia, hyperlactatemia, and hyperglycemia were attributed to a stress response. A selective loss of urea after exposure to FW resulted in decreased plasma osmolality. Conclusion Given the severity of the stress response and associated complications observed, hyposalinity treatments should be utilized with caution in this species. If this therapy is employed, the clinician is advised to be prepared to administer supportive care coinciding with the FW dip if necessary.
Article
Evolution of the vertebrate urinary system occurs in response to numerous selective pressures, which have been incompletely characterized. Developing research into urinary evolution led to the occurrence of clinical applications and insights in paediatric urology, reproductive medicine, urolithiasis and other domains. Each nephron segment and urinary organ has functions that can be contextualized within an evolutionary framework. For example, the structure and function of the glomerulus and proximal tubule are highly conserved, enabling blood cells and proteins to be retained, and facilitating the elimination of oceanic Ca+ and Mg+. Urea emerged as an osmotic mediator during evolution, as cells of large organisms required increased precision in the internal regulation of salinity and solutes. As the first vertebrates moved from water to land, acid-base regulation was shifted from gills to skin and kidneys in amphibians. In reptiles and birds, solute regulation no longer occurred through the skin but through nasal salt glands and post-renally, within the cloaca and the rectum. In placental mammals, nasal salt glands are absent and the rectum and urinary tracts became separate, which limited post-renal urine concentration and led to the necessity of a kidney capable of high urine concentration. Considering the evolutionary and environmental selective pressures that have contributed to renal evolution can help to gain an increased understanding of renal physiology.
Article
A novel thermally-responsive chloride-anions rich polyionic liquid (TPIL) hydrogel was synthesized and its potential in membrane-free osmotic desalination for saline and seawater was explored. The tunable Lower Critical Solution Temperature...
Chapter
The basic mechanisms of iono/osmoregulation, acid-base regulation, and homeostasis and excretion of nitrogenous wastes (ammonia and urea) are reviewed for freshwater fish, marine and euryhaline fish, and for special cases (marine hagfish and chondrichthyans). Six different examples are then explored where physiological understanding of environmental impacts on these processes has already informed regulatory and conservation strategies, or should do so in the future. These include: (i) the acid-rain crisis; (ii) survival of fishes in the acidic, ion-poor blackwaters of the Rio Negro; (iii) development of the Biotic Ligand Model for environmental regulation of metals; (iv) survival of fishes in highly alkaline lakes; (v) the commercial hagfish fishery; and (vi) the critical importance of feeding for osmoregulation in chondrichthyans. These lessons argue for a greater awareness of the wide-spread variation in the physical chemistry of natural waters, and the associated physiology of the fish that live there. This knowledge should be incorporated into regulatory strategies for both environmental protection and conservation of resident species at risk.
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Acute-stress situations in vertebrates induce a series of physiological responses to cope with the event. While common secondary stress responses include increased catabolism and osmoregulatory imbalances, specific processes depend on the taxa. In this sense, these processes are still largely unknown in ancient vertebrates such as marine elasmobranchs. Thus, we challenged the lesser spotted catshark (Scyliorhinus canicula) to 18 min of air exposure, and monitored their recovery after 0, 5, and 24 h. This study describes amino acid turnover in the liver, white muscle, gills, and rectal gland, and plasma parameters related to energy metabolism and osmoregulatory imbalances. Catsharks rely on white muscle amino acid catabolism to face the energy demand imposed by the stressor, producing NH4+. While some plasma ions (K+, Cl− and Ca2+) increased in concentration after 18 min of air exposure, returning to basal values after 5 h of recovery, Na+ increased after just 5 h of recovery, coinciding with a decrease in plasma NH4+. These changes were accompanied by increased activity of a branchial amiloride-sensitive ATPase. Therefore, we hypothesize that this enzyme may be a Na+/H+ exchanger (NHE) related to NH4+ excretion. The action of an omeprazole-sensitive ATPase, putatively associated to a H+/K+-ATPase (HKA), is also affected by these allostatic processes. Some complementary experiments were carried out to delve a little deeper into the possible branchial enzymes sensitive to amiloride, including in vivo and ex vivo approaches, and partial sequencing of a nhe1 in the gills. This study describes the possible presence of an HKA enzyme in the rectal gland, as well as a NHE in the gills, highlighting the importance of understanding the relationship between acute stress and osmoregulation in elasmobranchs.
Chapter
Because the salt concentration of body fluids in aquatic vertebrates differs from that of their environment, they face net influx or efflux of water and salt across their permeable skin or exposed membranes. In fishes, these diffusional movements of both salts and water largely involve the gills. Other vertebrates have less permeable body surfaces, but water and salts are gained in drinking that is incidental to eating prey, which also can be an important source of salt intake. Kidneys function importantly in freshwater fishes to remove excess water, and ions are actively transported inwards across gill tissue as well as acquired in food. Marine fishes tend to dehydrate in seawater, so they drink seawater to make up a water deficit and secrete excess salt across the gills. Marine elasmobranch fishes accumulate urea in body fluids to minimise the gradient for osmotic exchange and secrete excess ions via a specialised rectal gland that functions accessory to the kidney. In other vertebrates, inhabitants of fresh water must counteract a key problem of acquiring sufficient ions while excreting nitrogenous waste as ammonia or urea, whereas marine species must avoid excess salt intake while avoiding dehydration. Vertebrates without gills have evolved either extrarenal salt glands that excrete excess salt, or in the case of mammals, a specialised kidney that can excrete highly concentrated urine. Relatively few, non-fish taxa drink seawater as a route for water gain, while most others have dependency on dietary, metabolic or free drinking water. • Osmoregulation involves the maintenance of volume, distribution and ionic composition of body fluids in organisms. • With the exception of hagfish, extant vertebrates maintain osmotic concentrations of body fluids at levels that are roughly one-third that of seawater. • Aquatic vertebrates living in fresh water must counteract excessive influx of water and losses of ions to the surrounding environment, whereas those living in marine environments tend to dehydrate and gain excess salt. • Freshwater fishes eliminate excess water by means of producing a copious flow of dilute urine, while acquiring ions from surrounding water by transporter mechanisms located in the gills. • Marine fishes acquire needed water by drinking seawater and excreting excess salt gained by diffusion and drinking by transport mechanisms in the gills. • Marine vertebrates other than fishes and mammals have evolved extrarenal salt glands that excrete excess salts, and water is gained largely from dietary, metabolic and freshwater drinking sources. • Marine mammals excrete salt loads and urea from kidneys that have effective concentrating abilities, while gaining water from diet and metabolism.
Chapter
This chapter is intended to help maximize the information gained from diagnostic tests in fish. The text focuses on selecting appropriate tests, understanding their limitations, and evaluating sample quality. Specific topics include laboratory medicine (wet mounts, cytology, histopathology, hematology, and biochemistry), toxicologic and nutritional analyses, microbiology, and molecular and antibody-based diagnostics (PCR, DNA sequencing, immunohistochemistry, in situ hybridization, fluorescent antibody, and ELISA).
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The aim of this study is to investigate the effect of three daily fish feeding frequencies, two, four and eight times per day (FF2, FF4, and FF8, respectively) on growth performance of sea bass ( Dicentrarchus labrax )and lettuce plants ( Lactuca sativa ) reared in aquaponics. 171 juvenile sea bass with an average body weight of 6.80 ± 0.095 g were used, together with 24 lettuce plants with an average initial height of 11.78 ± 0.074 cm over a 45-day trial period. FF2 fish group showed a significantly lower final weight, weight gain and specific growth rate than the FF4 and FF8 groups. Voluntary feed intake was similar for all the three feeding frequencies treatmens ( p > 0.05). No plant mortality was observed during the 45-day study period. All three aquaponic systems resulted in a similar leaf fresh weight and fresh and dry aerial biomass. The results of the present study showed that the FF4 or FF8 feeding frequency contributes to the more efficient utilization of nutrients for better growth of sea bass adapted to fresh water while successfully supporting plant growth to a marketable biomass.
Article
In heterogeneous environments, mobile species should occupy habitats in which their fitness is maximized. Mangrove rivulus fish inhabit mangrove ecosystems where salinities range from 0-65 ppt but are most often collected at ∼25 ppt. We examined rivulus' salinity preference in a lateral salinity gradient, in the absence of predators and competitors. Fish could swim freely for 8 hours throughout the gradient with chambers containing salinities from 5-45 ppt (or 25 ppt throughout, control). We defined preference as the salinity in which the fish spent most of their time, and also measured preference strength, latency to begin exploring the arena, and number of transitions between chambers. To determine whether these traits were repeatable, each fish experienced three trials. Rivulus spent a greater proportion of time in salinities lower (5-15 ppt) than they occupy in the wild. Significant among-individual variation in the (multivariate) behavioral phenotype emerged when animals experienced the gradient, indicating strong potential for selection to drive behavioral evolution in areas with diverse salinity microhabitats. We also showed that rivulus had a significantly greater probability of laying eggs in low salinities compared to control or high salinities. Eggs laid in lower salinities also had higher hatching success compared to those laid in higher salinities. Thus, although rivulus can tolerate a wide range of salinities, they prefer low salinities. These results raise questions about factors that prevent rivulus from occupying lower salinities in the wild, whether higher salinities impose energetic costs, and whether fitness changes as a function of salinity.
Article
Serum protein electrophoresis (EPH) is used to assess relative concentrations of blood proteins in clinical and biological studies. Serum EPH fractions have been determined for elasmobranchs using mammalian albumin, alpha 1-, alpha 2-, beta-, and gamma-globulin fractions, and have been deemed fractions 1 through 5, respectively. However, serum EPH fraction concentration reference intervals (RIs) have not been widely established for different elasmobranch species. In this study, RIs for fractions 1 through 5 were determined from 45 wild-caught Nurse Sharks Ginglymostoma cirratum (27 females and 23 males) in South Florida. Serum samples were isolated from whole blood following caudal venipuncture. Body condition was also measured in the field to assess the relative health of the individuals sampled. There was no relationship between body condition and serum EPH fraction concentrations. In addition, there was no difference in body condition or serum EPH fraction concentrations between females and males. Total solids and total protein values were significantly different (P < 0.001). Nurse Shark serum EPH fraction 1 was found within the mammalian albumin migrating band distance and was negligible. Fraction 2 showed no peak in the mammalian alpha 1-globulin range. A thin, medium peak in the mammalian alpha 2-globulin range represented fraction 3. In the mammalian beta-globulin range, fraction 4 consisted of the majority of protein observed. It was represented by a smooth, broad peak. A short, medium broad peak in the mammalian gamma-globulin range represented fraction 5. The Nurse Shark serum EPH fraction RIs provided in this study may be utilized to clinically evaluate the health of Nurse Sharks in captivity and in the wild, and to compare the health of their populations around the world experiencin
Chapter
The antibody repertoire of cartilaginous fish comprises an additional heavy-chain-only antibody isotype that is referred to as IgNAR (immunoglobulin novel antigen receptor). Its antigen-binding site consists of one single domain (vNAR) that is reportedly able to engage a respective antigen with affinities similar to those achieved by conventional antibodies. While vNAR domains offer a reduced size, which is often favorable for applications in a therapeutic as well as a biotechnological setup, they also exhibit a high physicochemical stability. Together with their ability to target difficult-to-address antigens such as virus particles or toxins, these shark-derived antibody domains seem to be predestined as tools for biotechnological and diagnostic applications. In the following chapter, we will describe the isolation of anti-idiotypic vNAR domains targeting monoclonal antibody paratopes from semi-synthetic, yeast-displayed libraries. Anti-idiotypic vNAR variants could be employed for the characterization of antibody-based therapeutics (such as antibody-drug conjugates) or as positive controls in immunogenicity assays. Peculiarly, when using semi-synthetic vNAR libraries, we found that it is not necessary to deplete the libraries using unrelated antibody targets, which enables a fast and facile screening procedure that exclusively delivers anti-idiotypic binders.
Article
With the aim of reducing the ammonia content and improving the quality of meat from the blue shark, Prionace glauca, and salmon shark, Lamna ditropis, we evaluated the effect of soaking solutions containing 10% sucrose and 5% NaCl, with or without the addition of an aqueous extract suspension (AES) of rice bran (RB-AES), or fermented RB (FRB-AES) generated using Lactobacillus plantarum Sanriku-SU8 and Saccharomyces cerevisiae Misaki-1 (FRB-AES-Misaki-1), or S. cerevisiae Sanriku- SUY2 (FRB-AES-SUY2). RB is a major by-product of rice polishing. Although the effect of the soaking treatments on ammonia content and preference ranking were not clear in the fresh shark meats, there was a significant effect for meat refrigerated at 10 °C for 2 and 4 days (not-so-fresh meat). In particular, FRB-AES-Misaki-1 treatment raised the preference ranking for chub mackerel, Pacific cod and chicken breast meat. These results suggest that FRB-AES-Misaki-1 can be used as a potential starter for the pretreatment of meat from blue sharks and other fish species.
Chapter
1. Introduction2. Osmoconformers Versus Osmoregulators 2.1. Osmoconforming: Elasmobranchs in the Oceans2.2. Osmoregulating: Elasmobranchs at Low Salinities3. Properties of Organic Osmolytes 3.1. Inorganic Ions Versus Compatible Solutes3.2. Urea Versus Methylamines: Counteracting Solutes3.3. Salts Versus Methylamines: Counteracting Solutes3.4. TMAO Versus Pressure: A Piezolyte in the Deep Sea?3.5. Physicochemical Mechanisms of (De)stabilization3.6. Urea and Methylamines: Buoyancy3.7. Other Cytoprotective/Compensatory Properties3.8. Implications for Food Industry4. Metabolism and Regulation 4.1. Osmolyte Synthesis Versus Dietary Intake4.2. Retention of Osmolytes4.3. Development4.4. Cell Volume Regulation4.5. Hormonal Regulation5. Evolutionary Considerations6. Knowledge Gaps and Future DirectionsMarine elasmobranchs are hypoionic osmoconformers. Their extra- and intracellular fluids accumulate organic osmolytes for osmotic balance, mainly urea and methylamines such as trimethylamine N-oxide (TMAO), higher intracellularly at about 2:1 in shallow species, even in embryos and starvation. The relatively few euryhaline species reduce osmolytes only partially, and become hyperosmotic regulators, while permanent freshwater species have almost no organic osmolytes. Urea binds to and unfolds proteins while methylamines promote folding, thermodynamically counteracting each other at 2:1. Both also provide buoyancy. Deep-sea elasmobranchs increase TMAO and reduce urea, possibly because TMAO also counteracts protein-destabilizing effects of hydrostatic pressure. Recent studies show TMAO coordinates water molecules in a complex excluded from protein backbones (“osmophobicity”). This entropically favors folded protein conformations, and conteracts urea and pressure unfolding effects. Osmolytes are made in the liver or obtained from diets and retained by adaptations of gill, kidney, intestine, rectal gland. Regulatory mechanisms and evolutionary history are incompletely understood.
Chapter
1. Introduction2. Cardiovascular Function and Energetics 2.1. Oxygen Transport by the Cardiovascular System2.2. Responses to Hypoxia2.3. Elasmobranch Cardiac Anatomy2.4. Cardiac Metabolic Biochemistry3. Factors Controlling and Effecting Cardiovascular Function 3.1. Heart Rate and Stroke Volume3.2. Body Fluid Volume and Blood Pressure Regulation4. Signaling Mechanisms Effecting Blood Vessel Diameter 4.1. Gasotransmitters4.2. Endothelins and Prostaglandins (Prostacyclin)4.3. Autonomic Nervous System Signaling Mechanisms (Adrenaline and Noradrenaline)4.4. Other Vascular Signaling Mechanisms (Acetylcholine, Adenosine, CNP, Serotonin, Vasoactive Intestinal Polypeptide, Bombesin, and Neuropeptide Y)4.5. Substances Affecting Gill Blood Flow Patterns5. The Action Potential and Excitation–Contraction (EC) Coupling in Elasmobranch Hearts: The Influences of Environmental, Biochemical, and Molecular Factors 5.1. The Action Potential5.2. EC Coupling5.3. Effects of Catecholamines and Acetylcholine5.4. Effects of Temperature and Acidosis6. Practical Applications: Physiology in the Service of Elasmobranch Conservation 6.1. Global Climate Change and Ocean Acidification6.2. Surviving Interactions with Fishing Gear7. SummaryThe functional characteristics of elasmobranch and teleost cardiovascular systems are similar at routine metabolic rates. Differences do become apparent, however, in cardiovascular function of high-energy-demand species (e.g., mako shark and yellowfin or skipjack tunas) at maximum metabolic rates. Elasmobranchs have an autonomic nervous system separable into parasympathetic and sympathetic components. The vagus nerve has a major role in controlling heart rate, although sympathetic innervation of the heart and blood vessels is absent. Elasmobranchs increase cardiac output primarily by increasing stroke volume which, in turn, is primarily determined by ventricular end diastolic volume. End diastolic volume is determined by filling time and venous filling pressure; with the latter being effected by venous tone and venous capacitance. Blood volume and pressure in elasmobranchs are controlled by endocrine (e.g., renin-angiotensin, kallikrein-kinin, and natriuretic peptides) and paracrine (e.g., endothelins, prostaglandins, the gasotransmitters NO and H2S,) mechanisms. Excitation-contraction (EC) coupling in elasmobranch hearts largely fits the accepted model for vertebrates, although the rise in cytoplasmic calcium is primarily from trans-sarcolemmal sources, which includes Na⁺-Ca²⁺ exchanger (NCX). Some elasmobranchs populations are severely depleted due to the intersection of life history characteristics, unsustainable rates of fisheries-associated mortality, and environmental degradation. To address these issues effectively will require a better understanding of the elasmobranch cardiovascular physiology – including the ability of various species to withstand the physiological consequences of the increasing temperature and expanding hypoxic zones accompanying global climate change, and the severe acidosis and the plasma ionic imbalances resulting from interactions with fishing gear.
Article
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The white-edge freshwater whip ray Himantura signifer can survive in freshwater (0.7‰) indefinitely or in brackish water (20‰) for at least two weeks in the laboratory. In freshwater, the blood plasma was maintained hyperosmotic to that of the external medium. There was approximately 44mmoll - 1 of urea in the plasma, with the rest of the osmolality made up mainly by Na + and Cl-. In freshwater, it was not completely ureotelic, excreting up to 45% of its nitrogenous waste as urea. Unlike the South American freshwater stingray Potamotrygon motoro, H. signifer has a functional ornithine-urea cycle (OUC) in the liver, with hepatic carbamoylphosphate synthetase III (CPS III) and glutamine synthetase (GS) activities lower than those of the marine blue-spotted fan tail ray Taeniura lymma. More importantly, the stomach of H. signifer also possesses a functional OUC, the capacity (based on CPS III activity) of which was approximately 70% that in the liver. When H. signifer was exposed to a progressive increase in salinity through an 8-day period, there was a continuous decrease in the rate of ammonia excretion. In 20‰ water, urea levels in the muscle, brain and plasma increased significantly. In the plasma, osmolality increased to 571 mosmol kg - 1 , in which urea contributed 83mmoll - 1 . Approximately 59% of the excess urea accumulated in the tissues of the specimens exposed to 20‰ water was equivalent to the deficit in ammonia excretion through the 8-day period, indicating that an increase in the rate of urea synthesis de novo at higher salinities would have occurred. Indeed, there was an induction in the activity of CPS III in both the liver and stomach, and activities of GS, ornithine transcarbamoylase and arginase in the liver. Furthermore, there was a significant decrease in the rate of urea excretion during passage through 5‰, 10%o and 15‰ water. Although the local T. lymma in full-strength sea water (30‰) had a much greater plasma urea concentration (380 mmoll - 1 ), its urea excretion rate (4.7 μmol day - 1 g - 1 ) was comparable with that of H. signifier in 20‰ water. Therefore, H. signifer appears to have reduced its capacity to retain urea in order to survive in the freshwater environment and, consequently, it could not survive well in full-strength seawater.
Article
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Ureolytic activity was detected in liver homogenates of two carcharhinid shark species, Galeocerdo cuvieri and Negaprion brevirostris, employing 14C-labeled urea to monitor mineralization over 48 h. Significant (P < 0.05) urea hydrolysis was detected in liver homogenates within 48 h whereas no hydrolysis was detected in homogenates incubated with either ampicillin or the vibriostatic agent O/129, indicating bacterial mediation of the ureolytic activity. Urea hydrolysis could not be detected in blood samples. The autochthonous microflora of sharks has been found to contain ureolytic bacteria, and the present study supports the conclusion that they are present in organ tissues of healthy sharks but are not present in the blood.
Article
Full-text available
A review of past behavioral ultrasonic telemetry studies of sharks and rays is presented together with previously unpublished material on the behavior of the lemon shark, Negaprion brevirostris, around the Bimini Islands, Bahamas. The review, focusing on movement behaviors of 20 shark and three ray species, reveals that elasmobranchs exhibit a variety of temporal and spatial patterns in terms of rates-of-movement and vertical as well as horizontal migrations. The lack of an apparent pattern in a few species is probably attributable to the scarcity of tracking data. Movements are probably governed by several factors, some still not studied, but data show that food, water temperature, bottom type, and magnetic gradient play major roles in a shark's decision of where and when to swim. A few species exhibit differences in behavior between groups of sharks within the same geographical area. This interesting finding warrants further research to evaluate the causes of these apparent differences and whether these groups constitute different subpopulations of the same species. The lack of telemetry data on batoids and some orders of sharks must be addressed before we can gain a more comprehensive understanding of the behavior of elasmobranch fishes. Previously unpublished data from 47 smaller and 38 larger juvenile lemon sharks, collected over the decade 1988–1998, provide new results on movement patterns, habitat selection, activity rhythms, swimming speed, rate-of-movement, and homing behavior. From these results we conclude that the lemon shark is an active predator with a strong, apparently innate homing mechanism. This species shows ontogenetic differences in habitat selection and behavior, as well as differences in movements between groups of individuals within the same area. We suggest three hypotheses for future research on related topics that will help to understand the enigmatic behavior of sharks.
Book
This text lays out the principles of mechanistic comparative physiology in an ecological and evolutionary context. The subject of evolutionary physiology has been advancing considerably and this book will bring readers up to date on a number of new techniques, ideas and data. Topics include NMR spectroscopy and molecular biology, evolution and adaptation, phylogenetically-based analytical techniques and more.
Chapter
Introduction The osmotic composition of the body fluids of all sharks, skates, and rays is distinctly different from that of their environment (Table 9.1). Of special note is the extremely high concentration of urea that characterizes marine elasmobranch plasma (and cytoplasm). Enzyme function is maintained in the face of such high concentrations of urea by protein structural modifications to offset the denaturing effects of urea and/or by the presence of a stabilizing solute, trimethylamine-N-oxide (TMAO). Elasmobranch blood TMAO levels are usually approximately 75 mmol, but intracellular concentrations approach 200 mmol or 50% of urea levels, a ratio that has been shown to be of general occurrence (e.g., Hochachka and Somero, 2002). Because of the salt and water gradients across their permeable gill epithelium, these fishes must utilize various organs to maintain blood ionic and osmotic consistency (osmoregulation). Specifically, the osmotic gain of water across the gills of marine elasmobranchs must be balanced by renal excretion, and the diffusional gain of NaCl must be balanced by salt excretory mechanisms in the rectal gland, kidney, or gills. The few species of elasmobranchs that enter or reside in more dilute salinities (including freshwater) must balance the large osmotic gain of water by increased urinary water excretion. In addition, the diffusional loss of NaCl across the gills must be balanced by gill salt uptake mechanisms, and the kidney tubules must reabsorb salt to minimize urinary salt loss.
Chapter
The field of “elasmobranch endocrinology” began at the same time as the field of vertebrate endocrinology itself, when Bayliss and Starling (1903) used extracts from the intestines of sharks and skates to demonstrate the actions of secretin, the first described vertebrate hormone. Although perhaps coincidental, a pivotal role for sharks and their relatives in the birth of this field is prophetic to some extent, given that many vertebrate hormones appear to have first appeared in the cartilaginous fishes. Because sharks and their relatives occupy such a critical position in the evolution of the vertebrate endocrine system, studies on endocrinology of these fishes contribute to a better understanding of the roles that hormones exert in all higher vertebrates. Furthermore, because hormones regulate virtually all aspects of elasmobranch physiology, knowledge concerning the function of the elasmobranch endocrine system is essential for developing a full comprehension of how these fishes develop, grow, reproduce, and survive.
Chapter
Publisher Summary This chapter describes the role that salt-secreting organs play in fishes that are living in a hyperosmotic medium. Hypoosmoregulation is evidenced by those animals that can maintain the salt concentration of their extracellular fluid below that of the environment in which they live. Many hypoosmoregulating species inhabit marine or brackish waters, whereas others are located inland in saline lakes. Hyperosmoregulators on the other hand occupy terrestrial and/or freshwater habitats. The development of diverse anatomical structures within the various vertebrate classes that deal with salt and water balance suggest that at least two, and possibly more, independent solutions to the problem of osmoregulation have arisen. The evolution and development of the mammalian renal system appears to be an example of a system that couples the mechanism of regulating deviations of extracellular solutes and excess solvent within the same structure. The chapter reviews recent studies on cellular differentiation and its related biochemical changes in regard to the development of extrarenal osmoregulation. It also presents physiological studies of hypoosmoregutation in myxinoids morphological studies of salt secretion in petromyzonids
Article
Since the discovery of the phenomenally high urea content of the body fluids of cartilaginous fishes by Staedeler and Frerichs (1858), the unique osmoregulatory system of this vertebrate class has been studied by many investigators. In broad outline, the mechanisms are essentially similar in all three of the major subtaxa: the selachians, the batoids, and the holocephalans. A single exception is the genus Potamotrygon (fresh-water stingrays of South America and Africa), which has apparently lost the ability to concentrate urea even when transferred to salt water.
Article
The gill of fishes is modified for gas exchange, thereby providing a site for net movement of salts and water down their respective gradients. Specialized cells in the gill epithelium are joined by tight junctions of variable depth and express a variety of transporters and channels. These cells mediate NaCl extrusion in marine fishes and NaCl uptake in freshwater fishes. These transport steps also provide pathways for the extrusion of ammonia and acid vs. base equivalents. (C) 1999 Wiley-Liss, Inc.
Chapter
Study of urea transport in teleosts offers systems that are in a sense “stripped down” from the elasmobranch situation, such that facilitated diffusion, rather than active transport, may predominate. Likewise, different tissues within teleosts also appear to offer heterogeneity of function and additional model systems. The toadfish system appears to offer an advantage in studies of the temporal dynamics of urea transport regulation. In addition, the chapter focuses on urea transport in adult fish because urea transport during development. Earlier stages in development may in fact continue to offer novel and simpler systems for the study of urea transport. Finally, with the rapid progress in identifying urea transporters at the molecular level in both mammals and fish, phylogenetic perspectives of transporter evolution will be most informative.
Conference Paper
In general, marine elasmobranch fishes ( sharks, skates, and rays) maintain body fluid osmolality above seawater, principally by retaining large amounts of urea. Maintenance of the high urea concentration is due in large part to efficient renal urea reabsorption. Regulation of renal urea reabsorption also appears to play a role in maintenance of fluid homeostasis of elasmobranchs that move between habitats of different salinities. We identified and cloned a novel 2.7- kb cDNA from the kidney of the euryhaline Atlantic stingray Dasyatis sabina ( GenBank accession no. AF443781). This cDNA putatively encoded a 431- amino acid protein ( strUT- 1) that had a high degree of sequence identity ( 71%) to the shark kidney facilitated urea transporter ( UT). However, the predicted COOH- terminal region of strUT- 1 appears to contain an additional sequence that is unique among cloned renal UTs. Injection of strUT- 1 cRNA into Xenopus oocytes induced a 33- fold increase in [ (14)C] urea uptake that was inhibited by phloretin. Four mRNA bands were detected in kidney by Northern blot: a transcript at 2.8 kb corresponding to the expected size of strUT- 1 mRNA and bands at 3.8, 4.5, and 5.5 kb. Identification of a facilitated UT in the kidney of the Atlantic stingray provides further support for the proposal that passive mechanisms contribute to urea reabsorption by elasmobranch kidney.
Article
Marine elasmobranch fishes maintain high urea concentrations and therefore must minimize urea loss to the environment in order to reduce the energetic costs of urea production. Previous studies have identified a facilitated urea transporter in the kidney of the dogfish. We examined mechanisms of urea transport in the kidney of the little skate Raja erinacea using an isolated brush-border membrane vesicle preparation. Urea uptake by brush-border membrane vesicles is by a phloretin-sensitive, non-saturable uniporter in the dorsal section and a phloretin-sensitive, sodium-linked urea transporter ( K m=0.70 mmol l–1, V max=1.18 μmol h–1 mg–1 protein) in the ventral section of the kidney. This provides evidence for two separate urea transporters in the dorsal versus ventral sections of the kidney. We propose that these two mechanisms of urea transport are critical for renal urea reabsorption in the little skate.
Article
Marine elasmobranchs retain urea and other osmolytes, e.g. trimethylamine oxide (TMAO), to counterbalance the osmotic pressure of seawater. We investigated whether a renal urea transporter(s) would be regulated in response to dilution of the external environment. A 779 bp cDNA for a putative skate kidney urea transporter (SkUT) was cloned, sequenced and found to display relatively high identity with facilitated urea transporters from other vertebrates. Northern analysis using SkUT as a probe revealed three signals in the kidney at 3.1, 2.8 and 1.6 kb. Upon exposure to 50% seawater, the levels of all three SkUT transcripts were significantly diminished in the kidney (by 1.8- to 3.5-fold). In response to environmental dilution, renal tissue osmolality and urea concentration decreased, whereas water content increased. There were no significant differences in osmolyte and mRNA levels between the dorsal–lateral bundle and ventral sections of the kidney. Taken together, these findings provide evidence that the downregulation of SkUT may play a key role in lowering tissue urea levels in response to external osmolality.
Book
Hochachka P.W., Somero G.N. (2002) Biochemical adaptation: mechanism and process in physiological evolution. New York: Oxford University Press. 466 p.
Article
1. The major body fluid compartments were measured in two species of fresh-water Chondrostei, two species of fresh-water Holostei, three species of fresh-water Teleostei and seven species of marine teleosts. These were compared with previous measurements of an agnathan species and four species of Chondrichthyes.2. A general correlation was shown between the relative rates of respiratory movements and pulse rates, but neither of these appeared to be related to the taxonomic series. A faster pulse was more characteristic of marine than of fresh-water species.3. Plasma volume was measured by the dye dilution method, using T-1824. Whole blood volume was calculated from plasma volume and hematocrit. A progressive reduction in plasma and whole blood volume was noted, proceeding from the primitive to the more advanced groups. This is true both among the three classes of aquatic vertebrates and also among the three groups within the Osteichthyes. These volumes were remarkably similar in fresh-water and marine tel...
Article
The bacterial flora of 28 neritic sharks, comprising five species, was examined. Representatives of the genus Vibrio and related species were isolated, including V. alginolyticus, V. harveyi, V. furnissii, V. damsela, V. carchariae, and Vibrio spp. Vibrios accounted for 59 of 78 pure cultures identified to genus. The remaining 19 isolates comprised Photobacterium and Proteus spp., one strain of Escherichia coli, and three unidentified strains. Vibrios were found in all the organs and tissues that were cultured, indicating that these bacteria are part of the natural flora of sharks. Surprisingly, vibrios were frequently isolated from the kidneys, liver, and spleen of the sharks, strongly suggesting a bacterial-host relationship. Implications of this relationship are that vibrios may act as opportunistic pathogens for sharks and that vibrios may affect shark physiology, for example urea homeostasis.
Article
The gill of fishes is modified for gas exchange, thereby providing a site for net movement of salts and water down their respective gradients. Specialized cells in the gill epithelium are joined by tight junctions of variable depth and express a variety of transporters and channels. These cells mediate NaCl extrusion in marine fishes and NaCl uptake in freshwater fishes. These transport steps also provide pathways for the extrusion of ammonia and acid vs. base equivalents. J. Exp. Zool. 283:641–652, 1999.
Article
This chapter discusses the molecular and mitochondrial studies of the urea cycle in fish. A significant proportion of energy production in fish involves the catabolism and oxidation of proteins and amino acids. Consistent with their water habitat, the major end product of nitrogen metabolism in most fish is ammonia. Carbamoyl phosphate is the precursor for two major metabolic pathways: the urea cycle and pyrimidine nucleotide biosynthesis. The first step of the urea cycle in mammalian and amphibian ureotelic species is catalyzed by carbamoyl-phosphate synthetase I. The function of CPSase II is to catalyze carbamoyl phosphate formation as the first step in pyrimidine nucleotide biosynthesis. The utilization of the amide group of glutamine for the biosynthesis of carbamoyl phosphate in the glutamine-dependent CPSases involves the reaction of glutamine with a cysteine SH group on the enzyme to form a γ-glutamyl thioester intermediate, releasing ammonia, which reacts with an activated intermediate common to all CPSase. The unique co-functioning of glutamine synthetase and CPSase III in ammonia assimilation in the mitochondrial matrix probably reflects the adaptation of urea synthesis for the dual role of ureoosmotic and ureotelic functions.
Article
The evolutionary aspects of nitrogen metabolism and excretion in fishes continue to be an exciting and fruitful area for research, hypothesis generation, and testing. The scenario proposed by Griffith can be evaluated more completely because several significant findings of the past decade: (1) Although larval lampreys (ammocoetes) do not appear to express O-UC activity as predicted by Griffith, the O-UC occurs in embryos of teleosts that are typical ammonoteles as adults; (2) urea transport appears to be governed in fish by very specific transport molecules; (3) CPSase activities with some “I” isozyme characteristics, that is, enzymes with at least equal preference for ammonia as substrate, are found in higher teleostean fish; and (4) it is fully understand the cost of osmoregulation in ureosmotic versus hypoosmotic regulators, and the teleostean strategy may prove to be more economical.
Article
Peripheral plasma concentrations, metabolic clearance rates (MCR) and blood production rates (BPR) of 1α-hydroxycorticosterone (1-OH-B) were determined in female dogfish (Scyliorhinus canicula) under varying environmental conditions. The constant-infusion technique, using high specific activity tritiated 1-OH-B, was applied to measure the MCR, and BPR were derived from the product of plasma concentration and MCR at equilibrium. Urea plasma clearances and apparent BPR were assessed in a similar manner. Fish were adapted stepwise to 140, 120, 90, 80, 70, 60 and 50% normal sea water (about 1000 mosmol/l). In all cases 1-OH-B was the major corticosteroid, cortisol and corticosterone were sought but never detected. In environments of reduced osmolarity, plasma osmolarity, sodium, chloride and urea concentrations all declined, alongside increases in plasma concentrations, MCR and BPR of 1-OH-B. In fish held in environments at concentrations greater than normal sea water, plasma osmolarity, sodium, chloride and urea concentrations all increased. Plasma clearance of urea increased in fish held in environments more dilute than sea water, while it decreased in the more hyperosmotic waters. It is tentatively concluded that homeostasis of plasma composition, with particular respect to urea, is in part regulated by 1-OH-B in the dogfish. J. Endocr. (1984) 103, 205–211
Article
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Article
South American freshwater stingrays, which lack the high urea content characteristics of all marine and euryhaline elasmobranchs, fail to build up their urea concentration appreciably even when exposed to a saline environment gradually increased to a concentration approaching that of full strength sea water over a period of as much as six days. In a hypertonic external medium, osmolality of body fluid rises somewhat, but largely by an increase of sodium chloride rather than by urea accumulation.
Article
Urea and trimethylamine oxide (TMAO) have long been recognized as important osnuotic constituents of elasmobranch body fluids. Together, these organic solutes make up roughly one-half of the osmotically active constituents of elasmobranchs, allowing them to remain osmotically superior to the surrounding sea water. Eggs of elasmobranchs are nearly isosmotic to sea water ( Dakin, 191 1) , and like the adults, they contain significant quantities of urea (Kruken burg, 1888) . Smith ( 1936) , in reviewing urea retention and modes of repro duction in elasmobranchs, concluded that the tendency of elasmobranchs toward intrauterine development may be related to its adaptive advantage in protecting early embryos fronu urea loss. More recently, Price and Daiber ( 1967) , in their study of the intrauterine environment of ovoviviparous and viviparous forms, have concurred with Smith's conclusion. In what appears to be the only detailed study of the amounts of urea at various developmental stages of elasmobranchs, Needham and Needham (1930) found that in the dogfish Scyllium canicula, low amounts of urea are present when the eggs are laid, and that this urea is added to by the embryos as development proceeds (see also Needham, 1931) . Although Needham and Needham did not measure urea concentrations directly, they suggested that urea levels are lower in the undeveloped eggs than in the maternal fluids. They found that only a minimal amount of urea was lost from the developing embryo, and concluded that the increased urea content during development must be due to the excretion of urea by the embryo into the yolk. Their conclusions were rendered uncertain, however, by the lack of a good series of weighings for Scyllium embryos, and more importantly by their failure to measure urea in the embryos and yolks separately. In adult elasmobranchs, the major pathway of urea synthesis appears to be via the ornithine-urea cycle (Schooler et al., 1966). Recently (Read, 1968), evidence was presented of an ornithine-urea cycle early in elasmobranch develop ment. Embryos of the oviparous Raja binoculata and the ovoviviparous Squalus suckleyi were found to contain ornithine carbamoyltransferase and arginase, and the specific activities of these ornithine-urea cycle enzymes underwent marked increases early in development. Neither of these enzymes was found in the yolk, suggesting that any urea formed during development must be supplied by the embryo. This work thus supported the finding of Needham and Needham (1930) thatelasmobranchembryos are capableof producingurea.
Article
This chapter examines the hormonal control of gill Na+, K+-ATPase and chloride cell function. The secretion of excess sodium and chloride by teleosts in seawater is carried out by gill chloride cells. These highly specialized cells are characterized by a large, columnar appearance, numerous mitochondria, an extensive tubular system, an apical crypt, and mucosal–serosal exposure. The breakdown of ATP is detected in the presence and absence of ouabain. Herndon found that prolactin treatment of seawater-adapted tilapia resulted in a dramatic reduction in chloride cell size without changing chloride cell density. Chloride cell height and the proportion of cells spanning the opercular membrane were reduced, suggesting that these cells were effectively removed as chloride secretory cells. Based on reductions in opercular membrane conductance and short-circuit current following prolactin the treatment of seawater-adapted tilapia, Foskett postulated that prolactin reduces chloride cell numbers and active transport in the remaining chloride cells. Working with the closely related but stenohaline Nile tilapia (Oreochromis niloticus), Pisam found that prolactin injection caused the appearance of the smaller β-chloride cells that were previously absent from these fish in seawater.
Article
In all but 3 of 16 species of Amazon crustaceans and fishes, the activities of inorganic ions in the blood are 15–27% lower than expected. In most of the fishes, blood pH is higher than expected. In two of the fishes both departures are reversed by adding NaCl or KCl, but not H+, to the medium. Ammonia excretion varies inversely with blood and water salinity, and changes in blood ammonia induced by experimental exposure to air or high salinity can explain the changes in blood pH. Preliminary data suggest that the (Na+ + K+)-ATPase prepared from the gill of one teleost has a higher affinity for NH4+ than K+. It is suggested that at least some of the Na+ absorbed from the medium is exchanged for NH4+, and that binding to the ammonia molecule is responsible for at least some of the reduction of H+ activity in the blood.
Article
1. Juvenile freshwater stingrays of the family Potamotrygonidae are unable to survive in salinities in excess of 20.6‰ when gradually acclimated.2. No differences were observed in blood pH or hematological parameters when fish adapted to a salinity of 14.5‰ were compared with freshwater controls.3. Significant increases were found in serum sodium (21%), chloride (21%), calcium (48%), and magnesium (51%). Increases in total CO2 (16%), potassium (21%), and inorganic phosphorus (35%) were not significant on account of high variance. Serum osmolarity increased 69%.4. There was no apparent effect of salinity on serum total cholesterol, organically bound phosphorus, or total carbohydrates. Glucose contributed only 25% of the latter.5. Serum urea was low (1.1 mM/1) as previously reported, and the trend to increase in a saline environment was not osmotically significant.6. Freshwater stingrays are unique among elasmobranchs in possessing significant amounts of a protein with the electrophoretic mobility of human ...
Article
1. Water, urea and glucose reabsorption have been studied simultaneously using the inulin clearance method.2. Variations in filtration rate appear to be due to changes in the number of functional glomeruli, rather than to changes in the rate of function of individual units.3. Glucose reabsorption is not correlated in any way with that of urea.4. The main factor controlling the urea reabsorption is the concentration of urea occurring normally in the plasma. Attempts to increase the reabsorption of urea by raising the plasma level result in a depression of reabsorption not only of urea but of glucose and water as well. To some extent this reduced water reabsorption is offset by a decreased filtration rate, with the result that only a very moderate diuresis ensues.5. The percentage of the filtered urea which is reabsorbed varies with the concentration in the plasma, ranging from 70% to 99.5%, comparing quite favorably with the reabsorption of glucose.6. On the average, the actual amount of unabsorbed urea le...
Article
Comprehensive analyses have been made of the plasma and parietal muscle of the marine cyclostome Myxine glutinosa and of the chimaeraoid Chimaera monstrosa, and the sum of some 17 constituents compared with the directly determined osmotic concentration of plasma. Both Myxine and Chimaera plasmas are isosmotic with sea water within 2%. Ions account for at least 96% of the total concentration of the plasma in Myxine and about 60% in Chimaera, but the blood of the latter contains 332 mM urea, compared with 3 mM in Myxine. In muscle a similar divergence exists, the urea concentrations per kilogram muscle water being practically the same as in the respective plasmas of the two species. The mean values in millimoles of the other nitrogenous constituents of muscle are for Myxine and Chimaera (figures for latter in brackets), trimethylamine oxide 87 (189), betaine 65 (38), creatine and creatinine 30 (37), amino acids 291 (43). Using osmotic coefficients the calculated osmotic concentration of muscle exceeds that of plasma in Myxine and possible reasons for this are discussed. Estimates of inulin space in Myxine muscle have enabled intracellular concentrations of ions to be calculated. Analysis of Myxine bile shows it to have much higher concentrations of sodium, calcium and magnesium, and much lower chloride, than plasma. The resulting large anion deficit is presumably made up chiefly by the bile salt myxinol disulphate.
Article
In undiluted sea water, the lip-shark Hemiscyllium plagiosum excretes urine high in Mg++ and rectal-gland fluid with high concentrations of Na+ and Cl−. Urea is excreted largely by the gills (87%), but also by kidney (5%) and rectal gland (6%). In 50% sea water, the urine flow rate increases while the rate of excretion of Mg++ decreases. The rectal gland continues to secrete a fluid with Na+ and Cl− hypertonic to those of plasma. Branchial loss of urea is diminished as a result of a decline in plasma-urea concentration so that the clearance rate is unaffected. The U/P ratio for urea increases and the kidney excretes 48.4% of the total urea loss. However, this change in excretion of urea is too small to account for the concomitant decline in body urea content indicating that a reduction in the rate of biosynthesis of urea occurs.
Article
Published data on the diversity, life history, ecology, and status of freshwater and euryhaline elasmo-branchs was reviewed in the context of anthropogenic threats and principles of conservation biology. At least 171 species of elasmobranch, representing 68 genera and 34 families, are recorded from fresh or estuarine waters. Of these, over half are marginal in estuaries, less than one-tenth are euryhaline, and one-¢fth are obligate in fresh water. Obligate freshwater elasmobranchs are dominated by myliobatoid stingrays, of which two-thirds are potamotrygonids endemic to Atlantic drainages of South America. Freshwater and euryhaline elasmobranchs adhere to strongly K-selected life histories and feed at high trophic levels, similar to those of their marine relatives. However, freshwater and euryhaline elasmo-branchs are also subject to habitat constraints, notably more limited volume and physicochemical variability than the ocean, that may render them more vulnerable than marine elasmobranchs to the e¡ects of human activities. The greatest diversity and abundance of freshwater and euryhaline elasmo-branchs occur in tropical countries with enormous and rapidly increasing human populations, notably South America, West Africa, and south-east Asia. Knowledge of the biology, distribution, ecology, and status of freshwater and euryhaline elasmobranchs is frustrated by unresolved taxonomic problems, which are brie£y summarized. To clarify selected issues in the conservation of freshwater and euryhaline elasmo-branchs, special attention is given to sharks of the genus Glyphis, pristids, and potamotrygonids. To foster live release when possible as well as prevent discard of specimens and loss of data, an illustrated key to di¡erentiate Carcharhinus from Glyphis sharks is provided. Obligate freshwater elasmobranchs with limited geographic ranges are deemed most vulnerable to extinction, but euryhaline elasmobranchs that require access to the sea to breed are also at signi¢cant risk. Based on the foregoing data and principles of conser-vation biology, suggested action plans for the conservation of freshwater and euryhaline elasmobranchs and the conservation of freshwater habitats are provided.
Article
There is increasing evidence that urea movement across many epithelia involves more than passive diffusion. Of particular interest is the observation that urea transport across the erythrocyte membrane and across the vasopressin-stimulated urinary bladder of the toad occurs by facilitated diffusion, and can be selectively inhibited by phloretin and chromate. These inhibitory agents have been employed in studies of renal urea reabsorption by the spiny dogfish Squalus acanthias. Both agents inhibit urea reabsorption; the effect of chromate is of particular interest, since it blocks urea reabsorption to a proportionately greater extent than sodium reabsorption, and does so irreversibly.
Article
Under laboratory conditions, the gills of the striped dogfish Poroderma africanum (Gmelin) were studied as a possible site of ion and water transfer between internal and external media. Haematocrits showed that a drop in the external osmalarity produced increase in blood volume, measured as a decrease in blood pcv's (packed cell volume). Similarly, when fish were exposed to increased external osmolarity, the converse occurred, with resultant rise in pcv's. The use of phenol red showed that normally-fed fish did not drink the medium, and hence dilution of the blood was most probably due to water influx at the gills. Hypoosmotic fish (due to underfeeding) drank the medium in appreciable quantities, and dilution and concentration of external medium had a more pronounced effect on blood pcv's in these individuals. The pcv's of normally fed fish returned to initial values within 7 days after transfer to new medium is most cases, but hypo-osmotic specimens took longer to adjust to the new state of water balance. Surgical closure of rectal gland and urinary systems produced initial rises in serum sodium and chloride levels, but these reached equilibrium after 5 to 7 days, indicating compensatory regulation by some other organ, such as the gills. After removal of the sutures to the urinary systems of 3 fish, there was a noticeable drop in sodium and chloride levels of the serum in these individuals. All fish were kept for 14 days in the laboratory, with little change in blood composition (as measured) and with only the gills as regulatory organs in two of them. By using the radioisotopes Chloride-36 and Sodium-22, it was shown that both ions are lost at the gills, against the concentration gradient. Histochemical examination of gill tissue from several fish indicated that many cells contain high concentrations of chloride and are probably the site of chloride excretion. The number of such cells increased with increase in external salinity, and they were also abundant in tissue from hypo-osmotic specimens and those with inoperative urinary and rectal gland systems. From these findings it was concluded that the gills have a definite role in the ion and water balance of P. africanum.
Article
Pyjama sharks (Poroderma africanum) were exposed to a wide range of salinities, over which blood serum was analysed for osmolarity, chloride and urea concentrations. Fish were divided into two groups, those fed twice weekly (high intake), and those fed once a month (low intake). Both groups were exposed to the same salinity range. High intake fish showed the characteristic elasmobranch osmolarity picture, with serum values slightly hyper-osmotic at all times. Low intake fish, however, showed a degree of hypo-osmotic regulation. Serum values for both groups overlapped at very low salinities. Serum urea was also affected by diet, so that again two distinct sets of values were produced, again with overlap at the lower salinities. When previously well-fed fish were starved over a period of one month, serum urea and osmolarity decreased simultaneously. Consequently, it is felt that serum osmolarity is directly related to serum urea levels. Serum chloride was not found to be affected by diet, both groups showing the same change in blood values when exposed to the same change in salinity. It is shown, however, that a reduction in food intake, over a period of more than a fortnight, can reduce metabolic urea to the extent of depressing serum osmolarity and, hence, shift the ionic and osmotic equilibrium between the fish and the sea water. This may result in varying degrees of hypoosmotic regulation.
Article
1.1. Freshwater stingrays, Potamotrygon sp., were slowly acclimated to 40% sea water.2.2. Saline acclimation had no significant effect on the rate of urea biosynthesis.3.3. Rates of urea excretion were low and did not differ significantly in freshwater and saline acclimated rays. Total ammonia-n + urea-n was excreted primarily as ammonia-n in both groups.4.4. The rate of simultaneous total-body clearance of urea-14C and thiourea-14C in saline acclimated rays did not indicate that saline acclimation was accompanied by renal conservation of urea.5.5. Hematocrits and plasma urea concns did not differ significantly in fresh water and saline acclimated rays.6.6. Plasma sodium and chloride concns were significantly increased by saline acclimation.
Article
1.1. Activity levels of ornithine-urea cycle enzymes in the liver of Potamotrygon, a fresh-water ray, were one-half to one-twentieth those found in marine rays. The rate of incorporation of 14C-bicarbonate into urea by liver slices was also markedly reduced.2.2. In contrast to marine elasmobranchs, Potamotrygon did not actively reabsorb 14C-urea in its renal tubules.
Article
The focus of this chapter is on recent developments in our understanding of the expression of the urea cycle and the roles of glutamine synthetase (GSase) and glutamine-dependent carbamoyl-phosphate synthetase (CPSase III) in ammonia detoxification in fish, with emphasis on teleosts. Marine elasmobranch fishes have an active urea cycle, synthesizing and retaining urea for the purpose of osmoregulation. Well-characterized biochemical features uniquely different from the urea cycle in ureotelic terrestrial vertebrates that have served as a reference for studies on teleost fishes are reviewed. The majority of teleost fishes are ammonotelic, that is, ammonia is simply excreted directly across the gills into the surrounding aqueous environment. But, a functional urea cycle and ureotelism have been documented in a few adult species as adaptations to unusual environmental circumstances (stress, air exposure, high pH, exposure to high concentrations of ammonia). These adaptations are reflected in altered (1) CPSase III amino acid sequences and kinetic properties, (2) regulation of the levels of gene expression, and (3) specificity of expression with respect to organ localization (e.g., expressed in muscle instead of liver) and life-cycle stage. The emerging view is that all fish likely have genes for the urea cycle enzymes; teleost fish normally do not express the urea cycle enzymes (except perhaps during embryogenesis); fish are opportunistic in variations of adapting expression of the urea cycle to local environments; and fish are highly individualistic in the mechanisms they employ for adapting to varying environmental challenges, that is, expression of the urea cycle is only one of several possible strategies.