Tolerance of hypo-osmotic salinities in thirteen species of adult marine fish: Implications for estuarine fish culture

Thirteen species of adult marine fish were exposed to hypo-osmotic salinities for more than 2 weeks. Twelve species survived at 10‰, six species at 5‰ and three species at 3‰. No abnormal behavior was observed, but the water content of muscle increased in all species. Shallow-water, inshore species generally appeared to be more tolerant to changes in salinity than deep-water, offshore species. Tolerance of hypo-osmotic salinities varied within a single family or genus. For most species tested, the critical tolerance limit is about 5 to 10‰, and above 10‰ all species survived without apparent abnormal behavior. The present results suggest that many marine fish are more euryhaline than expected, and could be selected for farming in estuaries, provided that production is not reduced in fluctuating salinities. © 1983.link_to_subscribed_fulltex

Changes in biochemical composition in the red grouper, Epinephelus akaara (Temminck and Schlegel), and the black sea bream, Mylio macrocephalus (Basilewsky), during hypoxic exposure

1. 1. Red groupers and black sea breams exposed to 4 and 2.5 mg O2, 1- for 1-7 hr showed no increase in serum and tissue lactate concentration and only slight changes in other tissue metabolites and electrolytes. 2. 2. In both species subjected to 1 mg O2 1-, there was marked hyperglycaemia, hyperlactaemia, hepatic glycogenolysis and elevation of hepatic lactate content, but the lactate and glycogen contents of the muscles were unaffected. 3. 3. Both species can obtain enough oxygen to prevent anaerobiosis at 4 to 2.5 mg O2 1- and fermentation of hepatic glycogen to lactate is the principal pathway of energy production in 1 mg O21-1. 4. 4. In bothspecies,serum Na+,K+ and Ca2+ concentrations were unchanged after exposure to 4 to 2.5 mg O2 1-1 but all three parameters were elevated after exposure to 1 mg O1 1-1, suggesting that osmoregulatory failure could occur in extremely hypoxic conditions. 5. 5. The black sea bream, but not the red grouper, accumulated lipids in the liver in addition to lactate when exposed to all levels of hypoxia. © 1984.link_to_subscribed_fulltex

Metabolic and osmoregulatory changes in response to reduced salinities in the red grouper, Epinephelus akaara (Temminck & Schlegel), and the black sea bream, Mylio macrocephalus (Basilewsky)

Red groupers (Epinephelus akaara Temminck & Schlegel) and black sea breams (Mylio macrocephalus Basilewsky) were transferred from 30‰ into 3, 7, 12, 20, and 30‰ salinity. Fish were sampled at 0, 6, 24, 96, 168 and 336h after transfer. Serum osmolality, glucose, protein, Na+, K+, Ca2+, liver glycogen, liver protein, muscle water and haematocrit were determined. In general, transient disturbances in these variables were observed after transfer. For both species, no tissue hydration was observed upon acclimation to different salinities, whereas a progressive increase in haematocrit value was found as salinity decreased. Liver glycogen of both species, however, was higher in hypo-osmotic salinities. Serum Na+ of the red groupers declined upon acclimation to 7‰ salinity but the opposite was found for the black sea breams. The results indicate that both species are extremely euryhaline, and physiological stress is unlikely to occur within the salinity regime of 7 to 30‰ Comparatively, the black sea bream appears to be a more efficient osmoregulator. © 1982.link_to_subscribed_fulltex

Respiratory responses and tolerance to hypoxia in two marine teleosts, Epinephelus akaara (Temminck & Schlegel) and Mylio macrocephalus (Basilewsky)

The respiratory responses and tolerance of hypoxia were studied in two marine teleosts, the red grouper (Epinephelus akaara, a sluggish species) and the black sea bream (Mylio macrocephalus, an active species). Neither species showed abnormal behaviour or mortality when exposed to 2 mg O2 l-1 for 7 h. The black sea bream was, however, comparatively more tolerant when exposed to 1 mg O2 l-1, but tolerance of both species became similar under extremely hypoxic conditions (i.e. 0.5 mg O2 l-1). In contrast to most other teleosts, both species showed a reduction in opercular beating rate during hypoxia, and oxygen conformity was found in the range of 0.5 to 7.0 mg O2l -1. O2 dissociation curves were constructed, and the P50 value of the black sea breams (27 ± 5.6 mm Hg) was found to be much lower than that of the red groupers (50 ± 2.5 mm Hg). For both species, the general levels of venous PO2 showed a direct relationship to ambient PO2, and were markedly reduced after 1 h exposure to various levels of hypoxia. Compared with the red groupers, the black sea breams appeared to be more able to maintain its venous PO2 levels during prolonged hypoxic exposure. © 1984 Dr W. Junk Publishers.link_to_subscribed_fulltex

Metabolic effects of C21 steroids in female Epinephelus akaara (Teleostei: Serranidae)

International audienc

Aquatic hypoxia is an endocrine disruptor and impairs fish reproduction

There is increasing concern that certain chemicals in the aquatic environment can disrupt endocrine systems, leading to reproductive impairment and threatening survival of wild populations of invertebrates, fish, bird, reptiles, and wildlife. For the first time, we report that hypoxia is also an endocrine disruptor and poses a significant threat to the reproduction and hence sustainability of fish populations. Serum levels of testosterone, estradiol, and triiodothyronine significantly decreased in carp (Cyprinus carpio) upon chronic exposure to hypoxia. These hormonal changes were associated with retarded gonadal development in both male and female carp, reduced spawning success, sperm motility, fertilization success, hatching rate, and larval survival, indicating that adverse effects of hypoxia on reproductive performance resulted from endocrine disruption. Since aquatic hypoxia commonly occurs over thousands of square kilometers in aquatic systems worldwide, our results imply that endocrine disruption and reproductive impairment in fish may be a widespread environmental problem.link_to_subscribed_fulltex