Abstract: In order to understand the microdevelopment characteristics of intestine and liver of juvenile Cynoglossus semilaevis at different stages, paraffin sections, hematoxylin and eosin staining, microscopic observation and other methods were used to compare the intestinal microstructural characteristics of C. semilaevis with an average body weight of 2 g（W₂）, 26 g（W₂₆）, 59 g（W₅₉）, and 228 g（W₂₂₈）. The number of mucosal folds, the height of mucosal folds, the thickness of muscle layer, the relative density of mucinous cells and the height of monolayer columnar epithelium were measured. The results showed that the number of mucosal folds, the height of mucosal folds, the length of striatum margin and the single columnar epithelium of the four groups showed a consistent downward trend along the intestinal tract from front to back. Mucinous cells were distributed everywhere in the intestine, and their density gradually increased from front to back, and the change pattern of the four groups was consistent. Except for the number of mucosal folds and the density of mucinous cells, the other four morphological indexes showed a downward trend in the anterior part of the intestine, but gradually increased with ontogenetic development. The striatum border and the simple columnar epithelium of the midgut and hindgut decreased first and then increased in the four groups. The thickness of hindgut muscle layer decreased obviously, showing certain regularity. The liver was well developed in the four developmental stages, and the hepatocytes were polygonal. In conclusion, the intestinal and hepatic structures of C. semilaevis were gradually refined as the individuals developed, and in the W₂₂₈ group the intestinal and hepatic structures were well developed.

Key words: Cynoglossus semilaevis, Histology, intestine, liver