Metabolic and osmoregulatory changes during temperature acclimation in the red sea bream, Chrysophrys major: Implications for its culture in the subtropics

Abstract

Red sea bream, Chrysophrys major, were acclimated to 10, 20, 25 and 30°C for 21 days in seawater. At the end of the acclimation period, fish were sampled and changes in plasma, liver and muscle composition as well as changes in liver enzyme activities were monitored. Plasma osmolality, and Na +, K + and Mg 2+ concentrations were significantly elevated in fish adapted to 30°C. Plasma total α-amino acids, protein and lipid levels were also significantly higher in warm-acclimated fish. On the other hand, muscle and liver of the warm-acclimated fish had significantly lower amounts of total lipid and protein than the cold-acclimated animals. There was also a trend toward reduction in plasma glucose concentration in fish acclimated to higher temperatures; this was accompanied by a marked increase in liver and muscle glycogen storage. The activities of the key gluconeogenic enzymes, glucose-6-phosphatase and fructose-1,-6-diphosphatase, were markedly elevated in the liver of warm-acclimated fish. However, the activity of glucose-6-phosphate dehydrogenase was markedly elevated at 10°C. These data suggest that the metabolism of the red sea bream has been reorganized in response to temperature acclimation. At high temperatures, enhanced protein and lipid catabolism prevails and glycogen deposition results from elevated gluconeogenesis from protein. Metabolic and ionic disturbances occurring at 30°C suggest that it is undesirable to culture red sea bream at high temperatures. Their culture at low temperatures would have the advantage of conserving body protein at the expense of enhanced carbohydrate utilization.