The aim of this study was to determine the activity of digestive enzymes during the fry development of Rainbow trout (Oncorhynchus mykiss), which has a remarkable role in food digestion and absorption in the first feeding. The assessment of digestive enzymes activity of gastric (pepsin), pancreatic (trypsin, chymotrypsin, α-amylase and lipase) and intestinal (alkaline phosphatase) revealed that enzymes were available on the first day after hatching (DAH) but their activity showed no significant difference from hatching to day 12 (P > 0.05). An increased activity was seen between 12 and 18 DAH and this activity was significantly higher than the first 12 days (P < 0.05). In the primary stages after yolk sac absorption (after 20 to 31 days), enzymes activity showed an increased profile; however none of them showed a significant difference between 20 to 31 DAH (P > 0.05). These results could be used as a basis for formulating a suitable feeding and also selecting the best time for starting the feeding so that optimum nutritional values and cost-effectiveness are achieved
