| This study was designed to improve the understanding of the alimentary canal of Cynoglossus semilaevis. The alimentary canal of C. semilaevis can be divided into five sections, including oropharyngeal cavity, esophagus, esophagus and intestinal junction, foregut and hindgut. The structure and ultrastructure of alimentary canal of C. semilaevis were investigated using anatomical, histological and electronic microscopy methods. The number of mucosal folds, the height of mucosal folds, the thickness of muscle layers (longitudinal muscle and circular muscle), the density of mucus cells were measured and analyzed. The results showed that there was no obvious morphological stomach in C. semilaevis, evident by the lack of typical histological structure. However, a cystic structure, namly oesogaster, was formed in posterior part of esophagus following food intake, and oesogaster shrinked significantry during no food period. The principal structures of intestine canal include mucosal layer, submucosal layer, muscle layer and serosal layer. Oesogaster and intestine canal had little morphological difference based on electronic microscopic analysis. Each part of mucosal epithelial cell had mucus cells. Microvilli on the intestinal surface had no morphological difference. Microvilli of different sections, however, had differernces in length, with the longest on the foregut. The size and shape of mucus cells were also different. Top cytoplasm contained significant amount of mucous granules, while surface microvilli were relatively short, inward concaving and compact together. The goblet cells were found in the front segment of esophagus. In terms of mucous cell pattern, type Ⅲ mucous cell was the dominant cell type throughout the whole esophagus. Specifically, the mucous cells in oesogaster belonged to type Ⅲ, whereas foregut and hindgut segments mainly contained type Ⅳ and type Ⅱ mucous cells, respectively. The present study provides basic knowledge of digestive structure and mechanism of C. semilaevis and potentially can help to manufacture commercial diet for C. semilaevis. |
