Biochemical indicators of thermal stress in Tilapia aurea (Steindachner)

Tilapia aurea muscle and liver adenylate nucleotides, the adenylate energy charge (EC), plasma glucose, cortisol and chloride were monitored during acute and chronic temperature stress. Muscle EC is unaffected during acute cold water exposure but decreases significantly when tilapia are exposed to chronic, sublethal, low temperature stress. The decrease in EC is primarily the result of a decrease in ATP concentration. Plasma glucose and cortisol increase when tilapia are exposed to 11–12° C for 60 min, 11 days, and a 5-week period. Incomplete compensation is evident in 5-week acclimated fish since glucose and cortisol levels are intermediate between controls and acutely stressed fish. Acclimation to 35° C does not significantly affect plasma glucose and cortisol compared to controls (22° C). Plasma chloride is relatively unaffected by acute and chronic temperature stress. Liver adenylates are not significantly affected when tilapia are subjected to a sudden drop in water temperature (22° down to 11° C). EC is a useful indicator of chronic low temperature stress in T. aurea , while plasma glucose and cortisol are sensitive to both acute and chronic temperature stress.