Development of mucous cells in different parts of the digestive tract of larval and juvenile (1-45 dph) loach was observed and analyzed by histological sections and AB-PAS histochemical staining techniques.The results showed that:there were four types of mucous cells (typeⅠ,Ⅱ,Ⅲ and Ⅳ) during the development of digestive tract of loach.Mucous cells in digestive tract were first detected in buccopharygeal cavity and esophagus on 3 dph and appeared in every part of the digestive tract on 7 dph.Mucous cells were few before 10 dph and were widespread in digestive tract after 15 dph.As larvae grew,mucous cells changed from infantile types (typeⅠand typeⅡ) to mature types (typeⅢ and typeⅣ).According to the development and distribution of mucous cells in the digestive tract of fish,3 to 10 dph were critical periods of development of digestive tract in loach.Functions of digestive tract developed well on about 20 dph.In order to improve the survival rate of loach larvae and juvenile,appropriate managing measures based on the developmental process of the digestive tract was necessary.