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

Abstract

1. 1. Red groupers and black sea breams exposed to 4 and 2.5 mg O 2, 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 O 2 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 O 2 1 − and fermentation of hepatic glycogen to lactate is the principal pathway of energy production in 1 mg O 21 −1. 4. 4. In bothspecies,serum Na +,K + and Ca 2+ concentrations were unchanged after exposure to 4 to 2.5 mg O 2 1 −1 but all three parameters were elevated after exposure to 1 mg O 1 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.