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

The distribution of digestive enzymes was studied using histoenzymological methods in yellowtail and winter flounder larvae reared on three different diets: live food, weaned at day 15, or starved. Alkaline phosphatase, dipeptidyl peptidase IV, aminopeptidase M and esterase were present at 3 days post-hatch and became differentially distributed coinciding with morphological development. For larvae fed a live diet, activity of these enzymes was present in the intestine of both species and rectum of yellowtail flounder. Alkaline phosphatase was also present in the post-oesophageal swelling (stomach anlage) of winter flounder. Activity of all enzymes was absent in starved winter flounder larvae and a decrease in aminopeptidase M and esterase activity occurred in starved yellowtail flounder larvae. Acid phosphatase was not identified in either species. The effect of weaning on enzymatic activity was not evaluated fully as the larvae did not survive long enough after the introduction of the artificial diet to complete experimentation. (C) 1998 The Fisheries Society of the British Isles.