This study was conducted to determine the effects of photoperiod on egg hatchability, growth and survivability of hybrid catfish (Heterobranchus bidorsalis x. Clarias gariepinus) larvae, using hormone-induced spawning method. Eggs were stripped from two sexually matured and healthy female Clarias gariepinus of average weight of 1 kg/each and fertilized with milt from two sexually matured male Heterobranchus bidorsalis of average weight of 2 kg/each. An average of five hundred (500) eggs were introduced into each ten aquaria tanks of size 70 cm × 45cm × 40 cm/tank, using a predetermined spoonful estimation at five photoperiod regimes: (T 1) 24L : 00D (Light : Darkness); (T 2) 18L : 6D; (T 3) 12L : 12D; (T 4) 6L : 18D and (T 5) 00L : 24D in two replicates. Aquaria tanks were arranged in a flow-through system at a flow rate of 1.5 L/min with aerators to maintain good water condition. Provision of light during the night for illumination of the aquaria tanks was kept constant at 1200 1 ×, using solar panel (Mono)/inverter (Microtex) light energy. Growth and survivability of the fish larvae were monitored for six weeks. They were fed with laboratory-cultured live feed (Daphnia) to achieve maximum feed utilization. Percentage hatchability of eggs and best growth performance of fish larvae were significantly (p<0.05) highest (92.5%, 91.2 ± 0.21 mg) respectively in T 5 (00L : 24D), while percentage survivability of hatchlings was significantly (p<0.05) highest (94.4%) in T 3 (12L : 12D). It was observed in this study that the highest hatchability of eggs and optimum growth performance of hatchlings were under complete darkness, with reduced survivability of fish, as a result of observed cannibalism. The fish were photophobic. To achieve a balance result in terms of hatchability of eggs, growth and survivability of fish fry, it is suggested that incubation and hatching of eggs should be done under complete darkness, while rearing of fry should be under equal light and darkness exposure.
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