Effects of photoperiod on egg hatching and growth and survival of larvae fed with different diets in the Asian catfish, Clarias macrocephalus (Gunther), and the African catfish, C. gariepinus (Burchell).

摘要

Experiments were conducted in two Clarias species to determine the effects of: (1) photoperiod on egg fertilization and hatching, and (2) photoperiod and diet on larval growth and survival. Artificially fertilized eggs of C. macrocephalus and C. gariepinus exposed to combinations of different photoperiod regimes had similar fertilization rates (89-95%), but the highest hatching rates (70-76%) were recorded at 6 h light (6L):18 h dark (18D) photoperiod and the shortest hatchingtime (24-25 h) under continuous light (24L:0D). Ten-day-old larvae of both species were reared for 35 d under different photoperiods and fed three types of diet. Clarias macrocephalus larvae were the largest (p <0.05) and heaviest (p <0.05) under0L:24D photoperiod regardless of diet, but C. gariepinus larvae fed with diets of chopped fresh shrimp (D2) or chopped fresh finfish (D3) and exposed to 0L:24D photoperiod were significantly the largest (p<0.05) and heaviest (p<0.05). The highestsurvival rates were observed under photoperiods 18L:6D, 12L:12D and 0L:24D for C. macrocephalus and 12L:12D, 6L:18D, and 0L:24D for C. gariepinus. Survival rate was significantly higher in larvae fed diets D₂ and D₃ than those fed frymash alone (D₁). In conclusion, short periods of light increased egg hatching rate but continuous light shortened egg hatching time, while a combination of short periods of light and continuous darkness and fry mash supplemented with fresh feeds increased growth and survival of larvae in both catfish species.