THE PRODUCTIVITY OF NILE TILAPIA, OREOCHROMISNILOTICUS (L.) REARED UNDER DIFFERENT BROODSTOCK DENSITIES AND PHOTOPERIODS IN A RECYCLING WATER SYSTEM

Abstract

T he effect of three brood fish stocking densities (4, 8 and 12 fish / m 2) combined with three photoperiods (12, 15 and 18 hours/day) on the fry production of the Nile tilapia, Oreochromis niloticus (L.), were evaluated in a recycling water system. Treatments were arranged according to a 3x3 factorial design with three replicates giving a total of 27 spawning fiberglass tanks. Males and females with mean body weights of 160.3 and 112.0 g, respectively, were stocked at a male: female ratio of 1:3 in all tanks, and the experiment lasted for 120 days. The results showed thai breeders stocked at the lowest stocking density (4 fish / m 2) combined with the longest photoperiod (18 hours/day) had significantly higher (P<0.05) mean values for total fiy production, fry / kg female /day, fry / female /day, fry / m 2 / day, spawning rate and hatching rate than at 8 and 12 fish/nr broodstock densities exposed to the same photoperiod. Moreover, the productivity parameters of tilapia decreased in descending order with the medium and short photoperiods (15 and 12 hours/day, respectively) for all densities. The maximum percentage of yolk-sac and swim-up fry stages were obtained at the lowest stocking density combined with, the longest photoperiod. These findings are discussed to achieve optimum reproductive performance of Nile tilapia broodstock for fry production management. INTRODUCTION Many exogenous factors involving water temperature and light (intensity and duration) often interact to regulate the onset of gonadal maturation, the spawning season, spawning frequency and the calibration