Abstract:
Effect of thermal stress on some physiological activities were examined in male red
hybrid tilapia (Oreochromis sp.). The 24h loss of equilibrium temperature (LET50) and
lethal temperature (LT50) were preliminarily identified using water temperature regime
of 28, 30, 32, 34 and 36 °C, and determined at 31.6 and 33.6 °C, respectively. Fish were
then subjected to gradual acclimation at 1°C/8 h from 28 to 31 °C, and exposed for a
duration of 1, 7 and 14 days. The effect of sublethal thermal stress on the activities of
cortisol, HMG-CoA reductase, osmolality, ionic composition and total protein in
plasma; citrate synthase activities in brain, liver and kidney tissues, 11-ß hydroxylase
activity in testis tissue, as well as oxidative stress responses (lipid peroxidation,
superoxide dismutase, catalase, glutathione-S-transferase) in muscle, liver and kidney
tissues were investigated. Plasma cortisol was gradually increased from day 1 to day 7,
but decreased on day 14. Plasma HMG-CoA reductase and 11-ß hydroxylase in testis
tissue were also significantly increased (p < 0.05) on day 14.
