| Popis: |
In percid fi shes, the development of digestive structures and activities is quite similar to that of other carnivorous species (sea bass and sea bream). In most species at hatching, the digestive tract is a simple tube consisting of undifferentiated cells. The mouth and anus are closed and the esophagus is not connected with the intestine. Liver and pancreas are undifferentiated. Digestive enzymatic activities (pancreas, intestine) are detected shortly after hatching. According to histological and enzymatic studies, important changes occur around mouth opening (fi fth to seventh dph). The pancreas shows exocrine activity and the liver becomes functional with adipogenic and glycogenic functions. The primary stomach develops in pikeperch and even earlier in Eurasian perch. Pancreatic (trypsin, amylase) and intestinal (leucine-alanine peptidase, Alkaline phosphatase, aminopeptidase N) enzyme activities increase at mouth opening. Leucine-alanine peptidase (cytosolic enzyme) activity declines after mouth opening concurrently with the strong increase of the brush border membrane enzymes (Alkaline phosphatase, leucine-aminopeptidase N) activity indicating the development of the brush border membrane of intestinal enterocytes. The stomach development occurs between 15th and 20th dph in pikeperch and between 21th and 35th in Eurasian perch. Pepsin activity is detected only on day 29 in pikeperch as well as in Eurasian perch larvae and is concurrent with the development of gastric glands. The development of brush border membrane of the intestinal enterocytes and the gastric activity indicate that larvae acquire an adult mode of digestion. The digestive structures and activities can be affected by the nature and the diet composition. This aspect is also discussed in this chapter allowing an approach of the nutritional requirements of percid larvae. |
