Correlation between digestive system development and feedback regulation of cholecystokinin and trypsin in Megalobrama pellegrini larvae and juveniles

Megalobrama pellegrini (Tchang, 1930) are endemic economic fishes in the upper reaches of the Yangtze River, and the current understanding of their early development in captivity is minimal. To enhance the breeding of M. pellegrini in a recirculating aquaculture system (RAS), this study examined the development of the digestive system, fluctuations in cholecystokinin (CCK) levels, and tryptic enzyme activity during the early developmental stages of M. pellegrini —additionally, the research aimed to explore the correlations among these variables. A combination of histological, biochemical, and molecular methods was employed to detect M. pellegrini larvae from hatching up to 50 days after hatching (DAH). At 4DAH, the oropharyngeal cavity was opened, and the larvae entered the exogenous nutrition stage at 6DAH. At 12DAH, the functional structures of the intestinal tract gradually developed, the hepatocytes became uniform in size, and the nuclei of the pancreatic cells were clearly visible. At 24DAH, the intestinal tract appeared coiled and curled, and the gyrus was clearly visible. At 42DAH, the digestive tract and hepatopancreas structures became perfect, and the larvae entered the post-larvae stage at 45DAH. A negative feedback regulation was identified between CCK content and trypsin activity; however, the secretion pattern was oscillated by the development of the digestive system structure. In addition, the distribution of CCK in the digestive system of M. pellegrini at 60DAH was determined by in situ hybridization, and it was found that CCK was mainly concentrated in the foregut. The findings of this study can help optimize feeding strategies for the early developmental stages of M. pellegrini . They provide theoretical and practical foundations for the aquaculture of M. pellegrini in RAS and contribute to the research on freshwater fish concerning CCK. • Digestive system development of M. pellegrini was described from hatching to 50DAH. • CCK-trypsin feedback in M. pellegrini early development was governed by digestive tract structural development. • The distribution of CCK in the digestive system of M. pellegrini at 60DAH was mainly concentrated in the foregut. • CCK levels were genetically preset and food-independent in M. pellegrini pre-yolk exhaustion.