Abstract:Eleutheronema tetradacty is a tropical inshore marine fish species that belongs to the Polynemidae family. It has very high commercial values. Previous studies mainly focused on the stock structure and taxonomy of this species. However, the information about morphology and structural and functional biology has been limited, especially little is known about the development of the digestive system. In this study we applied the histological method to investigate this issue of E. tetradactylum aged Day 1 to Day 30 after hatching (DAH 1 to 30). Thus we may develop a better feeding strategy during artificial seedling rearing and improve the survival rate of the larvae. The experimental conditions were temperature 29–32℃，salinity 25–28, dissolved oxygen 4.80–5.5 mg/L，and pH 8.0–8.3. We found that on DAH 1, the digestive tube was not differentiated, and was composed of intestinal tubes that were attached to the abdominal wall and the yolk sac. On DAH 3, the yolk sac was fully absorbed, the larvae began feeding, and the digestive tube started to communicate with the outside. This indicated a switch from the endogenous nutrition to the exogenous feeding, and from this point, the larvae could maintain the growth by relative independent digestion and absorption through the gradually differentiated esophagus, stomach and intestine. The gastric gland and pyloric caeca appeared on DAH 15, which greatly improved the digestion and were the signs of the juvenile stage. On DAH 30, the structure and function of the digestive tract were well developed, which resembled that of the adults. The liver and the pancreas started to differentiate on DAH 2 and DAH 5 respectively, and they developed fast as the larvae grew. These observations suggested that the development of the digestive system was highly associated with the functions. Based on the characteristics of the digestive system, we further discussed issues in three major critical stages in the process of seedling rearing and proposed solutions for each stage.
