Effect of different photoperiod cycles on metabolic rate and energy loss of both fed and unfed young tilapia Oreochromis niloticus: Part I

Abstract

: To study the influence of different photoperiod cycles on the metabolic rate and energy loss of fed and unfed adult tilapia Oreochromis niloticus (bodyweight 102–107 g) at 28°C, four photoperiod cycles (i.e. 3L : 3D, 6L : 6D, 12L : 12D, and 24L : 24D) were applied. A computer-operated respirometer with a closed tank was used so as to prevent water from condensing from the air or evaporating into the air. A photoperiod-mediated metabolic cycle was demonstrated during the routine state in which the metabolic rate was higher during the light phase compared with during the dark phase for all photoperiods. The combined effects of photoperiod and feeding episodes acted as a strong Zeitgeber (cue or synchronizer) for synchronizing the daily rhythm in fed fish. Fish exposed to short photoperiod cycles showed a higher metabolic rate and energy loss compared with those exposed to longer photoperiod cycles. Mean oxygen consumption in the fed and unfed fish were 295.7 mg/kg per h and 149.8 mg/kg per h, respectively, during the 3L : 3D period; 286.5 mg/kg per h and 143.3 mg/kg per h during the 6L : 6D period; 262.2 mg/kg per h and 130.3 mg/kg per h during the 12L : 12D period; and 238.3 mg/kg per h and 120.4 mg/kg per h during the 24L : 24D period. The highest post-prandial increase in energy loss was recorded during the 3L : 3D period (56.2 kJ/kg per day), followed by 55.1 kJ/kg per day during the 6L : 6D period, 50.7 kJ/kg per day during the 12L : 12D period, and 45.4 kJ/kg per day during the 24L : 24D period. The study’s results demonstrated that the fish conserve energy when raised under longer photoperiod cycles.