Organogenesis of digestive system in Hapalogenys mucronatus during early development

Understanding the morphological and histological characteristics of the digestive system of larvae, juveniles and young fish of Hapalogenys mucronatus can provide a theoretical basis for its developmental biology, digestive physiology and feeding strategy. Through morphological observation, continuous tissue sectioning, and HE staining techniques, we examined histologically the development of the digestive system of the larvae, juveniles and young fish of H. mucronatus from 0^th−45^th day after hatching. The results show that at a water temperature of (24±2) ℃, the 0−2 day was the endogenous nutritional period, and the oropharyngeal cavity, esophagus and stomach had been penetrated. During the mixed nutrition period from 3−8 day, the cell masses of liver and pancreas had been formed, possible to feed on rotifers. Mmucus cells and taste buds were produced in the oropharyngeal cavity, mucosal folds were formed in the esophagus and intestine, and zymogen particles appeared in the pancreas. At this stage, the larvae had preliminary feeding and digestive abilities, and could fed rotifers and other bait. After 9 days of age, it was the exogenous nutritional period, with a curved intestinal tract, abundant mucosal folds and well-developed striated margins. The stomach was divided into a cardiac region, a gastric body and a pyloric region. Gastric glands and gastric pits were also formed, with a large number of hepatic sinuses, and zymogen particles visible in the pancreas. At this stage, it was possible to ingest some Moina mongolica and large copepods. From 22 to 30 days, each organ further developed, and after 35 days, the digestive system structure and function were basically improved. The development characteristics of digestive system at the early development stage of H. mucronatus are closely related to its feeding mode and function.