Distribution and ontogeny of digestive enzymes in larval yellowtail and winter flounder

The development of digestive enzyme activity was compared in 2 species of flounders, the yellowtail flounder, Pleuronectes ferruginea, and the winter flounder [Pseudopleuronectes americanus], subjected to 3 feeding regimes (live rotifer and algal diet, weaning onto a compound diet or starvation). Twelve larvae from each of the 3 groups were sampled, 1-2 h after the first feeding of the day, and individually processed for enzyme histochemistry. The results suggest that in the 2 species of pleuronectids examined, digestive enzymes are synthesized and functional during the earliest stage of postembryonic development, the yolk-sac stage. The spatial and temporal distribution of the enzymes, alkaline phosphatase, aminopeptidase M, dipeptidylpeptidase IV and non-specific esterase indicates that the functional segmentation of the digestive tract coincides with the morphological development for optimum nutrient digestion..