Ontogenetic development of digestive tract and digestive enzymatic activities in Squaliobarbus curriculus larvae

Squaliobarbus curriculus is an economically important freshwater fish. The ontogenetic development of the digestive system of S.curriculus larvae was studied histologically and enzymatically from hatching to 30days posthatching (DPH). Amylase, lipase, alkaline phosphatase and pepsin activities were detected from the hatching stage, indicating that these enzymes were genetically preprogrammed. Marked increases in intestinal amylase, trypsin and alkaline phosphatase activities between 10 and 20 DPH corresponded to feed acquisition and transformation. Larval development in S.curriculus could be divided into three phases: phase I (endotrophic period): 1-3 DPH; phase II (endo-exotrophic period): 4-5 DPH; and phase III (exclusively exotrophic period): from 6 DPH onward. At hatching, the digestive tract of the larvae was an undifferentiated straight tube. On 3 DPH, the digestive tract differentiated into the mouth cavity, oesophagus and intestine. On 6 DPH, feeding was totally exotrophic and the yolk sac was completely exhausted. During the growth of S.curriculus larvae, the intestinal mucosa formed and the number of goblet cells and microvilli increased, demonstrating maturation of the digestive system. The study about the digestive development of S.curriculus larvae will contribute to better larval-rearing strategies.