Effect of light intensity and photoperiod on Nile tilapia Oreochromis niloticus L. seed production

The objective of this study was to compare the effect of six light intensity/photoperiod combinations (2500 lux/18 h, 2500 lux/15 h, 2500 lux/12 h, 500 lux/18h, 500 lux/15h and 500 lux/12h) on seed production in the Nile tilapia Oreochromis niloticus L. Each combination represented a treatment and was triplicated in 0.4-m(3) fibreglass tanks within a recirculating water system. Water temperature was maintained at 29.0+/-1.0 degrees C. Males and females with mean body weights of 116.8 and 91.6 g, respectively, were stocked at a rate of eight fish/tank with a male to female ratio of 1:3. Seeds (eggs, sac fry and swim-up fry) were collected every 2 weeks. The experiment lasted for a total of 120 days. The results showed that the 2500 lux/ 18 h treatment produced significantly greater (P < 0.05) total seed/tank (4944), seed kg(-1) female-day(-1) (50.9), seed m(-2) day(-1) (40.3) and seed/ female day(-1) (6.7) than treatments with medium or short photoperiods (15 and 12 h day(-1) respectively) or lower light intensity (500 lux). The degree of spawning synchrony and percentage of the sac and swim-up fry stages were significantly higher in the 2500 lux/18 h treatment than in the other treatments. Under the conditions tested in this study, seed production and spawning synchrony in the Nile tilapia may be improved by subjecting breeders to a light intensity of 2500 lux and a photoperiod of 18 h day(-1).