Development of Some Digestive Enzymes and Alkaline Phosphatase Activities in Turbot Scophthalmus maximus Larvae and Juveniles

In order to provide a further theoretic basis for improving the survival rate, growth rate and optimizing the diet, the activities of some digestive enzymes and alkaline phosphatase were investigated during the larval and juvenile development of the turbot. The alkaline protease activity was identified after hatching. Acid protease was not present until the appearance of the gastric gland (about 15 days old). Three extremely low protease activities were observed during the period of the first feeding, the complete absorption of yolk sac and the transition from larva to juvenile. The noticeable amylase activity was present during the early stage of larvae and decreased significantly after they were 5 days old; from then on, it always remained at a low relative activity. The activity of lipase was very low before entering the young stage. The activity of alkaline phosphatase increased slowly from day 1 to day 50 but thereafter it showed a sharp increase. Important variations in specific activities of all the enzymes were observed during the period of development. At the end of metamorphosis, the activities of protease, lipase and alkaline phosphatase increased significantly, indicating the transition from juvenile to young and the improvement of the digestive system of turbot.