DEVELOPMENT OF DIGESTIVE-TRACT AND PROTEOLYTIC-ENZYME ACTIVITY IN SEA-BASS (LATES-CALCARIFER) LARVAE AND JUVENILES

The development of the digestive tract and changes in activity of proteolytic enzymes were studied in seabass larvae and juveniles. The stomach and pyloric sphincter did not start to be formed until 13 days after hatching (day 13) and were not completely formed until day 17. Prior to this, a high level of pinocytotic activity was found in the rectal cells of 6-day-old and 14-day-old seabass larvae indicating that protein macromolecules were being absorbed by these cells. The pH of the anterior gut (the presumptive stomach before the stomach was formed) in early larvae was alkaline (pH 7.7 on day 8); on day 17, the pH of the stomach had become acidic (pH 5.0) and pepsin-type enzyme activity in the larvae had increased from an initial basal level. By day 22, the acidity of the stomach had become more pronounced (pH 3.7) and the pepsin-type enzyme activity had become well established. Digestion of dietary proteins by the larvae and the possible contribution of live food to the process are discussed.