Observations on the Seed Production of the Tilapia Oreochromis spilurus (Gunther) under Different Spawning Conditions and with Different Sex Ratios

Abstract

Two experiments were conducted to compare the seed production of the tilapia Oreochromis spilurus (Gunther) under ambient and controlled (water temperature of 30.0 :I: 1.0 °C and photoperiod of 14 h day·1) conditions. Twelve 2.0 x 2.0 x 0.5 m fiberglass tanks were used and six tanks were assigned to each spawning condition. In Experiment 1, each tank was stocked with 30 females. Males were added to ob­tain male to female sex ratios of 1:3, 1:4 and 1:5. Each sex ratio in each spawning condi­tion was duplicated and the experiment lasted for 14 months. In Experiment 2, twelve breeders were stockerl per tank at 1:3 male to female sex ratio with two tanks per sex ratio. The experiment lasted for 10 months. In both experiments, seed collection was car­ried out every two weeks. Results showed that sex ratios have no significant effect (P>0.05) on the seed produc­tion of 0. spilurus under both breeding conditions. In both experiments, daily mean seed production under ambient conditions reached its lowest levels during the coldest (Decem­ber-January) and warmest (August) months of the year while, under controlled conditions, it was significantly higher (P<0.05) during the same months. Seed production was more evenly spread throughout the year. No significant difference (P>0.05) was observed in the overall seed composition (eggs, yolk-sac fry and swim-up fry) of females under both breed­ing conditions. The results of this study indicate the potential of extending the restricted six-month spawning season of 0. spilurus in Kuwait to a year with controlled water temperature and light duration.