Sixty juveniles of the African catfish, Clarias gariepinus (Burchell), were reared in triplicate under three different photoperiods: 24 h total darkness (24D:0L); 24 h total light (24L:0D); 12 h darkness and 12 h light (12D:12L). The latter served as the control in order to investigate the effects of light duration on the growth, body coloration, and feed conversion efficiency of the juveniles. Water quality in the tanks was also measured. Significant (P < 0.05) increases in body weight, specific growth rate, and food conversion efficiency were recorded among the fish cultured under 24D:0L, followed by 24L:0D, while those under 12D:12L showed the least growth increase. The high growth increase recorded in the 24D:0L was attributed to better food conversion efficiency and the suppression of swimming activity, aggression, and stress in the dark. All these enabled more energy to be converted to body weight. The body coloration of these fishes was also darker than in the other photoperiods. This was due to the physiological response of the fish in the dark to increase the stimulation and production of melatonin. The simple, low-cost technique of a 24D:0L photoperiod should be applied to ponds in order to achieve faster growth of this fish in less time.
