Studies On The Structure And Development Of Digestive Systerm Of Hucho Taimen

Ripe male and female Hucho taimen whose bellies were ventricose, soft and ptotic were selected respectively as parents fish in March of 2005, 2006 and 2007. Zygotes were obtained from the fish by artificial fertilization. Specimens of digestive system were collected from embryo as well as fry, juvenile, fingerling and adult fish which were get through artificial incubation and breeding. The paper aims to study the structure and phylogenesis of digestive system in Hucho taimen. It was also investigated that the effects of PNR(the point of no return) on the growth of Hucho taimen juvenile. The results as follows:1.The digestive system of adult fish was composed by Cavum oropharyngeum, esophagus, stomach, intestines and pyloric caeca. Cavum oropharyngeum contained many geny-teeth, palato-teeth, vomerine teeth, pharyngeal teeth and hyoid teeth. The mucous layer of cavum oropharyngeum contained number of mucous cells and few taste buds; Esophagus which was pachy and short have developed muscle layer. The shape of stomach was like a"V", and the stomach was divided into cardiac part, fundus gastricus and pyloric part obviously. Stomach was lined with mucous layer, stratum submucosum, muscle layer and placenta percreta from inside to outside. Inferior part of the mucous layer contained a greate number of gastric gland. The structures of the intestines and the pyloric caeca were almost the same.They were lined with mucous layer, stratum submucosum, muscle layer and placenta percreta. The mucous layer contained number of mucous cells and eosinophilic granular which was used for protein digestibility. Liver was comparatively large, and it was independent from the pancreas.2. When the cumulative temperature reached 7.83℃·d the cleavage stage had been completed; And the blastula stage were completed at the cumulative temperature of 40.04℃·d; After the gastrocoel stage and the neurula stage, the archistome began to block; When the cumulative temperature reached 262.69℃·d, the larva hatched out, and became the fry. At 14 days after hatching, solid center cell mass which was the rudimentumof the digestive tract appeared below the notochord. Digestive tract further developed and had apparente two layers after 26 days hatching, and the muscle layer differentiated obviously. There also appeared a great quantity of conjugate nuclei inclusions which were in dividing phase as well as absorptive cell. At day 28 after, the whole digestive tube was unblocked except the symphysis between the cavum oropharyngeum and the oesophagus as well as the archos. And the liver get bigger. The mouth of the fry had opened. After 10 day the goniozygomatic and the exognathion had already been calcified, mouth can open smoothly. at the anterior extremity of the oesophagus the cavity could be found. The mitosis of gastric epithelium cells were increased and 5～7 mucosal foldings can be found. Central veins and liver cell cord were apparent in liver. At 20 days after hatching, mucous cells can be found in mucous layer of the oesophagus. A constriction apperaed in the dilatate part between stomach and intestine. Liver cells in the central part of the liver were seriously vacuolated. At day 66 post-hatching, the structive of the stomach and intestine in fry was the same as those in adult fish. Stomach was divided into cardiac part, fundus gastricus and pyloric part obviously. The foregut and the rectum were all lined with mucous layer, submucous layer, muscle layer and serous membrane.3. The body of the sharp-set juveniles were melanized and thin, but their heads were big. Their body heights were lower than that of control group. Their total length were shorter. The melanin pigment in stomach intestine was dense. When they were hungery for a long term, their pars encephalica sagged, and they would eat each other. PNR(the point of no return) of the juvenile was at day 39 post-hatching. The digestive system of hungry juvenile developed slowly. To be hungry for 15 days, the stomach muscle layer thickness of juvenile reached the maxmize of 51.50μm. Then it would get thinner to be hungry for 33 days. It would reach the minimize of 42.22μm. The structure of gastric gland was destroyed severely,and it was appeared as the atrophy of gland cell, the reduction of the number of the gastric glands which were in bad order ,and the muscle fiber of stomach was raritas and reticulated. To be hungry for 21days. Mucous layer thickness of stomach was maximizing 34.16μm. Then the height of the epithelium mucosae cell would get lower. It reached the nadir of 18.38μm at the day 33. Mucous layer and muscle layer of intestines completely developed when juveniles were hungry for 21 days, their thicknesses were maximum of 31.71μm and 21.96μm. Along with the experiment was carried on, acidophilia particles became raritas and the number of them got smaller. The height of Intestine epithelium got lower. Duodenal duodenal and many mucous cells were broken. To be hungry for 33 days, the heights of mucous layer and muscle layer reached the nadirs of 20.00μm and 24.42μm. By day 27, the demarcations between liver cells bacame indefinite, and the nucleoli which were atrophie or disintegrated deviated or cohered to the nuclear membranes. And that made part of the nuclear membrane got thickened and vacuolization.