Study On Morphology Of The Digestive System Of Hyriopsis Cumingii And The Characteristics Of Digestive Enzymes

Triangle sail mussel (Hyriopsis cumingii) is the most important freshwater pearl mussels in China. Both the enlarging farming scale and overloaded aquacultural water resource lead to a serious regression of germplasm resources of Hyriopsis cumingii. Although it has been for a long time that Hyriopsis cumingii was used to commercially exploited for freshwater pearl culture in China, a number of basic theories associated with aquaculture have not yet been clarified, particularly in digestive physiology of Hyriopsis cumingii. In this study, the morphological structure of digestive system, the optimal pH value of digestive enzymes activity, and the variation of digestive enzymes under different algal culture conditions were investigated, which will provide basic imformation on shellfish digestive physiology and alga'l cultivation.The morphological anatomy of the digestive system was studied by using anatomy and optical microscope techniques. The results showed that the digestive system of Hyriopsis cumingii was constituted of digestive gland and enteron. The former only contained the liver, while the latter included the mouth, esophagus, stomach, foregut, midgut, hindgut, rectum, anus, and so on. The mouth, which had a pair of triangular piece lip on two sides, was under anterior adductor muscle. Esophagus was very short at the back of the mouth. The volume of stomach was small. A pair of liver surrounded the stomach. Contactto crystal rod (rod-like structure of glial). was contacted with gastricshield. The intestine was constituted of inner tube and outer tube. According to the structure, the intestine could be divided into four parts: foregut, midgut, hindgut and rectum. The foregut was joined to the stomach. Both the crystal rod and the foregut were wrapped into one tube during getting out of the stomach, and twisted in the visceral mass. The midgut was constituted from the suddenly small part of foregut to the swelled part of hindgut. The above two parts were joined by capsule, which was full of food and also twisted in the visceral mass. The hindgut was began with the swelled part through into the heart, which was constitute of one capsule filled with food. The rectum was from the heart to anus, and wrapped in a pipe which was full of food and waste. The anus was located at the posterior adductor muscle and the outlet pipe.The organization structure of digestive system of Hyriopsis cumingii.The liver, as digestive diverticula, was the most important digestive organs, which was composed of a number of branches of small blind tubes by biopsy technique. According to the structure and function, the liver could be divided into common hepatic duct and tubule. The enteron was constituted of mucosa, submucosa and serosa, and did not have muscle. However, there was a muscle layer outside of the intestinal tract, which was gradually thickened from the beginning to the end. Mucous layer was constituted of long cylindrical cells with cilia. In different parts of the enteron, the structure of mucosa layer were slightly different from that of submucosa layer. The mucosa epithelium of hindgut was irregularly rough. The gastric mucosa epithelium was little thicker than intestinal mucosa epithelium. Besides, the intestinal epithelium contained caliciform cells, which could secrete mucus, especially in the hindgut.The activities and optimal pH values of protease, amylase and cellulase were determined by using Folin-phenol, iodine-starch colorimetry and DNS techniques in the liver, stomach, foregut, midgut, hindgut and rectum. The results showed that the protease activity was from high to low as follows: stomach> liver> foregut> midgut> hindgut> rectum. The optimal pH value of all organs was 7.0, except the rectum 7.5. The amylase activity was from high to low as follows: stomach > hindgut> liver> midgut> foregut> rectum. The optimal pH value of liver, stomach and hindgut was 7.5, while that of foregut, midgut and rectum was 7.0. The cellulose activity was from high to low as follows: stomach> midgut> liver> hindgut> foregut> rectum. The optimal pH value of liver is 5.0, while that of the others was 4.6. Compared test was showed that activities of protease, amylase, cellulase in two groups were significantly different under different conditions of live algae.