STUDIES ON BIOCHEMICAL RESPONSES OF TABLE SIZED LABEO ROHITA (HAMILTON, 1822) TO THE THERMAL EXPOSURE AT CRITICAL MAXIMUM TEMPERATURE (CTMAX)

Water temperature of aquatic bodies is gradually getting warmer and may pose threat for survival, health and production of fish in future. The critical temperature maximum (CTmax) is the tool to estimate the upper limit of thermal tolerance of fish but information on biochemical events occurring at CTmax are limited for our selected fish, Labeo rohita. In the present study, biochemical alteration of table sized Labeo rohita (Rahu) was examined at CTmax (42.67±0.53ºC) against fish kept at acclimation temperature (30.5±1.0ºC) by increasing water temperature continuously at the rate of 0.28°C minute-1. Significant alteration was observed for all studied biomolecules with increased glucose and triglycerides and declined protein and cholesterol in serum at CTmax. Hormones also altered with increased value for thyroid hormones and decreased value for cortisol, however the alteration was significant only for T4. In liver glucose, triglycerides and cholesterol level was higher but protein was less at CTmax. Increased transaminase enzymes activities (GPT and GOT) in liver may have increased the production of the glucose from tissue protein. At CTmax, alteration in metabolic activities (higher amount of glucose and triglycerides in serum) for energy production and onset of heat shock responses (higher expression of hsp70 gene in liver) were occurred in Rahu. In this study, CTmax was 42.67±0.53ºC and warming tolerance was 12ºC indicating that Rahu can tolerate sudden increment of water temperature of a few degrees beyond present habitat temperature, although for few moments.