Combined Effect of Heat Shock and Chlorine Fails to Elicit Acquired Thermal Tolerance in Labeo rohita Spawns

An experiment was conducted to delineate the effect of heat shock and chlorine on the biochemical responses of Labeo rohita spawns for evaluating acquired thermal tolerance. Spawns were equally distributed in three different groups i.e., group 1 heat shock (37 °C) without chlorine, group 2 heat shock (37 °C) in chlorinated water and group 3 control in ambient water (28 °C). Following 1-h stress, the animal was transferred to ambient water conditions to study the recovery from stress at different sampling hours i.e., 0, 2, 4, 8, 14, 24 and 48 h. Stress parameters viz., glucose, lactate dehydrogenase, malate dehydrogenase and adenosine triphosphatase were measured for both the experimental groups and compared with the control. At the end of 48 h, the recovering spawns in the respective experimental groups were subjected to temperature higher than 37 °C in order to check for thermal tolerance and induction of cross protection. Their survivability rates were checked after exposure to 38, 39, 40, 41 and 42 °C. The result indicated that the spawns in group 1 recovered within 24 h wherein heat shock alone imparted higher thermal tolerance in them leading to 100 % survival at 40 °C; however the fishes in group 2 did not recover even after 48 h and demonstrated only 30 % survival at 40 °C. In both experimental groups, none of the fish survived the exposure to 42 °C. The results indicate that the combined effect of heat shock and chlorine has more pronounced effect on L. rohita spawns and fails to develop acquired thermal tolerance.