Effects of thermal stress on physiological responsess in male red hybrid tilapia oreochromis

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.