The aim of this study was to investigate the ontogeny of digestive enzymes and effects of photoperiod on pancreatic enzyme activity in rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) alevin and fry. After hatching, 3600 individuals of first-feeding alevin with a mean (±SD) mass of 119 ± 0.01 mg were reared in plastic tanks at four photoperiod levels (llight (L) : dark (D) cycle) for 6 weeks. Each replicate contained 300 alevin. Photoperiod treatments consisted of 14 h L : 10 h D, 10 h L : 14 h D, 4 h L : 20 h D, and 24 h L : 0 h D. During the rearing period, environmental variables including water temperature, oxygen, and pH were checked. Random sampling of alevin and fry was done at 0, 1, 3, 5, 8, 10, 15, 20, 25, 30, 39, and 44 days after the beginning of the first feeding (equal to 18, 19, 23, 25, 28, 30, 35, 40, 45, 50, 58, 63 days post hatching (dph)). The digestive enzyme activities in alevin and fry had a similar variation trend with age at all photoperiod levels. The specific activities of trypsin, chymotrypsin, and α-amylase at 24 h L : 0 h D were significantly higher than other treatments, but there was no significant difference in specific activity of lipase among treatments. The results demonstrated that growth, feeding efficiency, and digestive enzyme activity improved with longer exposure to photoperiod in rearing conditions.
Differences in stress and disease resilience related to emergence time for first feeding in farmed rainbow trout (Oncorhynchus mykiss)
