Characterization of the ultrastructure of the gastrointestinal tract mucosa, stomach contents and liver enzyme activity of the pinfish during development

Carnivorous juveniles (< 16 mm L-S) of pinfish Lagodon rhomboides apparentl y lacked gastric glands in the stomach while larger fish, intermediates (30 33 mm L-S) and herbivorous adults (> 80 mm L-S) had numerous gastric gland s. Two cell types were identified in the gastric glands of larger fish: muc ous secreting cells and secretory cells which had ultrastructure features t ypical of digestive enzymes and acid secretion. Lipid absorption occurred t hroughout the cacca and intestine in all sizes of fish, h Microvilli found on the rectal epithelial cells of the intermediate and adult pinfish occurr ed on stalks and were possibly associated with water reabsorption. Liver en zyme activities changed in small fish (26 39 mm L-S) compared to the adult fish. Alanine amino transferase (ALT) and fructose diphosphotase (FDP) acti vities declined while pyruvate kinase (PK) activities increased significant ly. These changes were consistent with a change in diet from a carnivorous (high protein) diet in juveniles to an omnivorous (lower protein) diet dete rmined by stomach content analyses. (C) 2001 The Fisheries Society of the B ritish Isles.