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Abstract
The catfish

Ompok bimaculatus

(butter catfish) has recently gained importance as an aquaculture candidate species because of its delicious taste, higher nutritional value and market demand. A significant problem in butter catfish aquaculture is its inability to voluntarily spawn in captivity. This experiment was conducted to study the impact of photoperiod on the voluntary spawning of O. bimaculatus in the pre-spawning season (April) in captivity. A total of 80 broodfish were equally distributed (n = 20; F = 10 and M = 10) into four photoperiod treatments: natural condition (control), 12:12 light:dark (L:D), 15L:9D and 9L:15D were stocked in rectangular tanks, and the experiment was carried out for 45 days. Light intensity was maintained at 1000 lx throughout the study for all treatments, except the control. The fish were fed a commercial diet (40% crude protein and 6% crude lipid) at a rate of 3% of body weight, twice a day, for 45 days. Ovasis™ was used for hormone induction to study induced breeding. Broodfish reared under natural photoperiod (control) did not respond to voluntary captive spawning. A complete voluntary captive spawning response was observed in the 12L:12D broodfish, and partial success was observed in the 15L:9D and 9L:15D broodfish. The fertilization rate, hatching rate and survival were significantly (p < 0.05) higher in the 12L:12D broodfish group than those in the broodfish group. Hence, the photoperiod regime of 12L:12D with 1000 lx light intensity would be ideal for voluntary captive spawning and can be elected for maximum seed production in the pre-spawning season. The present study showed that photoperiod manipulation and fixed light intensity stimulate advanced gonadal maturation and voluntary captive spawning of butter catfish, which can help seed production throughout the year.