Abstract：To investigate the structural characteristics and analyze their functional and dietary differences and similarities of the digestive system of loach Sinogastromyzon szechuanensis and Metahomaloptera omeiensis hangshuiensis, morphology and histology were observed in the digestive system of S. zechuanensis with average body length of (5.18±0.11) cm, and M. omeiensis hangshuiensis with average body length of (4.96±0.25) cm collected from the Jiangjin section of the Changjiang River, Chongqing, and the Luowang Town section of the Baishui River, Zhaotong City, Yunnan Province in December 2021 by morphological, histological, and histochemical (AB-PAS) methods.It was found that the alimentary canal was comprised of the oropharyngeal cavity, esophagus, stomach and intestine, with diminutive oral fissure and a stomach configuration resembling the letter “U”.The intestinal morphology in S. szechuanensis was characterized by a straight forward folding pattern, in contrast to the intricate organization observed in M. omeiensishangshuiensis, as indicated by intestinal coefficients of 1.43±0.08 and 2.46±0.21, respectively, signifying a substantial disparity. The pancreas was distributed throughout the hepatic tissue.The structural and characteristic attributes of the digestive systems in both species were evidently tailored to accommodate omnivorous feeding habits. In the oropharyngeal cavity, four distinct types of mucous cells were observed. The esophageal mucosa featured multiple layers of type Ⅰ and type Ⅲ mucinous cells within its epithelium. Conversely, there was predominant mucous cell type Ⅲ, with the presence of gastric glands limited to the cardiain gastric mucosa without goblet cells. Transitioning from the foregut to the hindgut, a gradual decrease in mucosal fold height, columnar cell and striated border thickness was noted, while goblet cell density exhibited an incremental trend. Four categories of mucinous cells were found in the foregut, without type Ⅰ mucous cells in the midgut and hindgut. In the case of S. szechuanensis,several key distinctions were observed, including significantly high densities of the four types of mucous cells in the oropharyngeal cavity, elevated density of type Ⅲ mucous cells in the caecum and pyloricus, increase in thickness of the pyloric muscle layer, and the posterior intestinal submucosa. The stomach of S. szechuanensis was also characterized by an abundance of gastric glands, housing all four types of mucous cells, featuring a typical portal area within the liver tissue. Conversely, for M. omeiensis hangshuiensis, notably density of heightened goblet cells was observed in the posterior intestine as compared to S. szechuanensis. It is postulated that S. szechuanensis primarily exhibits carnivorous tendencies within its omnivorous dietary preferences, while M. omeiensis hangshuiensis is more inclined towards omnivorous-herbivorous feeding habits.
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2024, Vol. 43 
