Abstract:To clarify the digestive and physiological characteristics in the early developmental stage of Seriola aureovittata, the activity of different digestive enzymes (lipase, amylase, trypsin, and alkaline phosphatase) were studied. Fertilized eggs and 1- to 60-day-old larvae and juveniles of S. aureovittata were selected as the research objects. The relationship between total length and days after hatching was also studied. The results indicated that the total length of larvae and juveniles increased with age within 60 days after hatching and increased significantly after 25 days. Lipase, amylase, and alkaline phosphatase were detectable during the embryonic stage while trypsin was detected in newly hatched larvae, which indicated that S. aureovittata can digest lipid, carbohydrate, and proteins before feeding. The specific activities of lipase and alkaline phosphatase increased rapidly after hatching (P<0.05), reached a peak at (5.88±0.45) and (5.56±0.41) U/mg, respectively at first feeding. The amylase activity reached its peak at (1.59±0.02) U/mg on day 7. The specific activity of trypsin increased slowly after hatching, and reached the highest value ((1098.67±24.03) U/mg on day 15 (P<0.05). Lipase, alkaline phosphatase, and trypsin were basically stable in the visceral mass of juvenile fish. However, the activity of lipase, alkaline phosphatase, and trypsin increased with the development of S. aureovittata. The amylase activity in the visceral mass of juvenile fish showed a downward trend and was basically stable at a lower specific activity level. The results of this study showed significant changes in various digestive enzyme activities during the development of larvae and juveniles, which were closely related to the development stage and feeding habits. The digestive enzymes were detected in early larvae that had not yet eaten food which was considered that the digestive enzymes were maternal in origin and not from exogenous food. The lipase, alkaline phosphatase, and trypsin activities in juveniles significantly increased, which reflect the improvement of intestinal structure and digestive function and the increasing demand for fat and protein.
