The effect of photoperiod on stomach and intestinal digestive enzymes in Rainbow trout (Oncorhynchus mykiss) larvae and juvenile

This study investigated the ontogeny of some digestive enzyme and explored the effects of photoperiod on stomach (pepsin) and intestine enzyme activity (alkaline phosphatase and N-amino peptidase) in rainbow trout (Oncorhynchus mykiss) larvae juvenile. About 3600 larval rainbow trout in first feeding (18 days after hatching) with an average initial weight 119±0.009 mg were distributed in plastic tanks in four treatments (300 larvae in each replicate). Four light treatments consisting of 14 to 10 h, 10 to 14 h, 4 to 20 h and 24 to 0 h (light: dark), were compared in triplicates for 6 weeks.. Finally, a random sampling from larvae was undertaken on days 1, 3, 5, 8, 10, 15, 20, 25, 30, 39 and 44 days after the onset of first feeding. According to the results, the digestive enzymes activity in fish larvae and juveniles had a similar change trend with age at all photoperiods. In addition, at the end of experiment, the specific activity of pepsin and N-amino peptidase were the highest in 24h Light treatment, but there was no significant difference in specific activities of alkaline phosphatase (p>0.05). The results demonstrated that growth and digestive enzymes activity of rainbow trout larvae and juvenile are improved by applying of longer photoperiod in rearing conditions.