DISTRIBUTION AND ONTOGENY OF DIGESTIVE ENZYMES IN LARVAL YELLOWTAIL AND WINTER FLOUNDER

The distribution of digestive enzymes was studied using histoenzymolog ical methods in yellowtail and winter flounder larvae reared on three different diets: live food, weaned at day 15, or starved. Alkaline pho sphatase, dipeptidyl peptidase IV, aminopeptidase M and esterase were present at 3 days post-hatch and became differentially distributed coi nciding with morphological development. For larvae fed a live diet, ac tivity of these enzymes was present in the intestine of both species a nd rectum of yellowtail flounder. Alkaline phosphatase was also presen t 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 identifie d in either species. The effect of weaning on enzymatic activity was n ot 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.