Effect of water temperature on early life history of African sharp-tooth catfish, Clarias gariepinus (Burchell, 1822)

Early life history of Clarias gariepinus from egg fertilization to full yolk sac resorption was studied at 33 temperatures within the thermal range 17.4-35.6 degrees C. The viable temperature range for embryonic development; temperature at which ontogeny is hypothetically arrested (15.4 degrees C); viable temperature range for larval development; and the number of effective day-degrees for the embryonic and larval periods were determined. The early life history of C.gariepinus was found to be temperature-dependent in terms of the onset of key ontogenetic events, developmental rate, survival rate, and size of larvae. The length of the incubation period, hatching period, size of larvae at hatching, time to first intake of exogenous food, and time to full yolk sac resorption with and without exogenous feed supply, were inversely proportional to the temperature within the optimal temperature range. In terms of survival, the zone of thermal tolerance for early life history of C.gariepinus ranged from 18.9 to 33.2 degrees C with the thermal optimum from 22.9 to 30.3 degrees C, typical for thermophilous species. Temperature ranges of 20.6-22.9 degrees C and 30.2-33.2 degrees C were found to be suboptimal. Temperatures below 17.5 and above 35.1 degrees C may be considered lethal during the embryonic period, and those below 18.9 and above 33.2 degrees C are lethal during the larval period.