Effects of Water Temperature on Activities of Metabolic Enzymes of Juvenile Siganus guttatus
Background: Temperature is one of the most important environmental factors affecting the survival, growth and metabolism of fish. The current study was aimed to study the effects of water temperature on the metabolic enzyme activities of juvenile Siganus guttatus. Methods: The juveniles were domesticated at 28±1°C for two weeks and then the temperature was adjusted to the target temperature groups (31°C, 27°C, 23°C and 19°C) by the gradually increasing or decreasing temperature with the change rate of 2°C per day. The experiment lasted for 70 d. At the end of the experiment, the fish were anesthetized and all the livers were dissected on ice plate and stored in the refrigerator at -80°C for the determination of enzyme activity. Result: The activities of glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT), hexokinase (HK) and pyruvate kinase (PK), lipoprotein lipase (LPL) and hepatic lipase (HL) tend to be increased with the reduction of temperature. The above enzymes activities in 19°C group were highest. The activity of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) and citrate synthase (CS) was lowest in 19°C. These results suggests that 19°C had exceeded the suitable temperature range for juvenile S. guttatus. At low temperature, S. guttatus mainly use fat for energy, but less anaerobic metabolism for energy.