Does light duration (photoperiod) have an efect on the mortality and welfare of cultured Oreochromis niloticus and Clarias gariepinus?

Abstract

One hundred and eighty juveniles of Oreochromis niloticus with a respective smean total length and weight of 7.30 ± 0.5 cmand 7.05 ± 0.5 g and 180 fry of Clarias gariepinus with a mean total length and weight of 14.90 ± 0.1 cm and 32.10 ± 0.5 g were separatelycultured in 3 replicates in 18 plastic tanks (1 × 1 × 0.5 m; 200 L), 9 for O. niloticus and 9 for C. gariepinus, for photoperiods of 24 L: 0D, 0 L: 24 D, and 12 L: 12 D for 13 weeks. Mortality and welfare impairment were evaluated daily. Mortality was signifcantly higher(P < 0.05) for the 0 L: 24 D photoperiod among O. niloticus and signifcantly higher (P < 0.05) for the 24 L: 0 D photoperiod among C.gariepinus. In general, mortality was signifcantly higher (P < 0.05) among O. niloticus than in C. gariepinus, with mortality being veryhigh in the frst 5 weeks of culture in the 2 species in all 3 photoperiods. Mortality was probably due to stress in the tanks arising frompoor acclimatization to the environmental conditions, feeding inhibition, cannibalism, and maladjustment to the light/dark rhythmiccycle. Te 0 L: 24 D photoperiod had a profound efect on the welfare of the juveniles of O. niloticus, and 24 L: 0 D compromised thewelfare of the juveniles of C. gariepinus, as shown by the nonintrusive welfare indicators. Te 2 unfavorable photoperiods manifestedin stress conditions that caused injuries and afected swimming activity, behavior, coloration, and growth. If welfare challenges arisingfrom photoperiodism are taken into account during culture of the species with photoperiodic manipulation, the species mortality willbe decreased and the farmer s profts will increase.