| The mud loach (Misgurnus anguillicaudatus) is a small freshwater teleost belonging to the family Cobitididae of the order Cypriniformes. It is an important commercial species in China. Because of its high values of nutrition and economy, the loach was welcomed among the people, artificial culture of this species has gained more popularity recent years. Technique for its large-scale artificial propagation has been applied well. However, mass mortality in larvae rearing has been a major bottleneck in seed breeding. In order to enhance the success of larvae rearing of mud loach, we need to know the ontogeny of its digestive system and respiratory organs thoroughly. The purpose of this study was to understand both the morphological structure and function development during the ontogeny of mud loach. We also want to understand the ontogenies of air-breathing organ and respiratory organ in addition. HE stain, AB stain, PAS stain, AB-PAS stain were adopted in this study. We hope that this information would provide fundamental knowledge for larvae rearing management for this species. The main results are shown as follows:By adopting HE staining, the study focuses on the ontogeny of morphological structure of digestive system in loach larvae. At1DPH (Day Post Hatching), the buccopharynxgeal cavity was closed, the digestive tract appeared as a straight tube. At3DPH, the mouth opened, taste buds and goblet cells could be found, the digestive tract was developing quickly, two different regions could be distinguished in the esophagus, and mucosal folds appeared in intestine, hepatocytes developed rapidly. Lipid vacuoles appeared in intestine on4DPH and numerous acidophilic supranuclear vacuoles appeared on5DPH. The buccopharynxgeal cavity was well developed and the first goblet cell was detected in intestine. Some blood vessels could be found on15DPH in intestine and the liver and pancreas had developed well. At20DPH, there were many visual differences among the three parts of the intestine, the height of the epithelial cell layer was progressively reduced from anterior intestine to posterior intestine, as were the number and depth of the mucosal folds. More capillaries with red blood cells could be found just beneath the epithelial layer of the mid-intestine and posterior intestine. The organizational structure became similar to the adult gradually after20DPH.Development of mucous cells in different parts of the digestive tract of larval loach was observed and analyzed by the method of histological sections and AB, PAS and AB-PAS staining techniques. There were four types of mucous cells (type Ⅰ,Ⅱ,Ⅲ and IV) during the development of digestive tract of loach, the first mucous cells were found in buccopharynxgeal cavity and esophagus on3DPH. Mucous cells were few before10DPH and were widespread in digestive tract on15DPH. As larvae grew, mucous cells changed from infantile types (type I and type II) to mature types (typeⅢ and typeⅣ). According to the study, it was a period of rapid development of mucous cells about15DPH, functions of digestive tract developed well on about20DPH.By morphological observation on the changes of external gills of loach larvae, we found that: the first see of external gills was18hours after hatching, and bloodstream could be seen at that time. Then the external gill developed rapidly, bloodstream increased, both number and length of external gills increased and got maximal on2DPH. From3DPH, the external gills got shorter. On5DPH, the inner gill filament appeared. On7DPH, the external gills got significantly shorter. On15DPH, the external gills disappeared and the operculum could close completely.According to the result of the present study, we concluded that it was a critical period of loach from3DPH to20DPH, especially from15DPH to20DPH because that in this period the air-breathing function formed. In order to improve the survival rate of loach larvae and juvenile, appropriate managing measures basing on the developmental process of the digestive tract was necessary. |
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