DEVELOPMENT OF THE DIGESTIVE ORGAN SYSTEM IN JAPANESE FLOUNDER IN RELATION TO METAMORPHOSIS AND SETTLEMENT

During metamorphosis and settlement the digestive system of Japanese f lounder (Paralichthys olivaceus) exhibits various morphological featur es that include: differentiation and development of gastric glands and pyloric caeca coupled with partial degradation of the pancreas; invol ution of the liver; inflation of the gall bladder, and shortening of g ut epithelium height. Pepsin-like enzyme activity increases markedly a s metamorphosis proceeds, while trypsin-like enzyme and amylase activi ties drop significantly. High percentage of newly settled wild flounde r at the climax phase of metamorphosis have empty stomachs, indicating that feeding ceases while the gut is undergoing reorganization. These findings suggest that the morphological and functional changes of the digestive system that occur during metamorphosis of Japanese flounder relate to the drastic diet shift at settlement from zooplanktonic to benthic prey.