MORPHOLOGY, HISTOLOGICAL STRUCTURE CHARACTERISTICS AND DIGESTIVE ENZYME ACTIVITIES OF THE DIGESTIVE TRACT OF PAMPUS ARGENTEUS

To study the relationship between feeding habits and structural characteristics and functions of the digestive tract of Pampus argenteus, we used morphological, histological, histochemical (AB-PAS) and enzymological techniques to investigate the morphological and histological structures, mucous cell distributions and digestive enzyme activities of the digestive tract of P. argenteus. Our results showed that the digestive tract of P. argenteus consist of six parts: an oropharyngeal cavity with a short tongue, an ellipsoidal esophageal sac, a stubby esophagus, a U-shaped stomach, a multiple coils intestine with index 2.03 and a large number of pyloric sacs. In the oropharyngeal cavity, several taste buds and three types of mucus cells were detected in the stratified squamous epithelium of tongue. The esophagus sac, esophagus, stomach, pyloric sac and intestine are all composed of mucosal layer, submucosa, muscle layer and serous membrane. The esophageal sac contains primary and secondary protrusions, which were covered with stratified squamous epithelium, a special structure (horny spur) and a large numbers of type Ⅳ mucus cells were observed in the epithelium, and the esophageal sac showed a high level of pepsin activity. The esophagus showed high mucosal folds with a stratified squamous epithelium, a large number of mucus cells were detected in the epithelium, which are dominated by type Ⅳ. The stomach was abundant in gastric glands, no mucus cell was observed in it. A high level of pepsin activity was detected in the stomach. The intestine shows a single columnar epithelium, four types of mucus cells were observed in the epithelium, which are dominated by type Ⅰ. The total density of mucus cells increased from anterior intestine to middle intestine, but decreased from middle intestine to posterior intestine. while the height of mucosal fold was first decreased and then increased from anterior intestine to posterior intestine. The intestine also showed high level of trypsin, lipase, amylase and alkaline phosphatase activities. The structure of pyloric sac was similar to intestine, it enhances the digestive and absorptive functions of intestine. In conclusion, the morphological and histological characteristics, mucous cell distributions and digestive enzyme activities in the digestive tract of P. argenteus adapted to its omnivorous feeding habits.