Morphological And Histological Studies On The Development Of The Digestive System In Odontobutis Sinensis

The O.sinensis belongs to the order Perciformes,Odontobutidae,the genus Odontobutis.Its wild resources are in decline,because of heavy fishing and the degradation of the habitat environment.Therefore it is necessary for large-scale farming in order to meet the strong market demand.The bait package is one of the key techniques for artificial breeding.In this experiment,we studied the digestive system characteristics of adult Odontobutis sinensis and the development of the digestive system during embryonic and juvenile phases by means of anatomical and histological methods.The results are as follows.1.The digestive tract of O.sinensis consists of the oropharyngeal cavity,oesophagus,stomach,and intestine,according to the external curvature and constrictions of the digestive tract.The stomach is type I,very short.The intestine forms 2 curves,and can be divided into foregut,midgut,hindgut and rectum.The foregut is enlarged.Anatomical observation of welldeveloped longitudinal folds in the stomach.Forming a flap at the pylorus-intestine that extends into the foregut.Intestine valva forms between the hindgut and rectum,extends into the rectum.The wall of the digestive tube(except for the oropharyngeal cavity)consists of a mucosal layer,a submucosal layer,a muscular layer and a plasma layer.The main features are the variation in the type and number of cells in the mucosal layer and the thickness of the muscularis.The mucosal epithelium of the oropharynx is distributed with mucus cells and taste buds.The mouth flap has abundant taste buds.The mucosal epithelium of the oesophagus distributes abundant mucus cells.The transverse longitudinal muscle in the posterior segment of the oesophagus gradually decreases and a small amount of smooth longitudinal muscle appears.The lamina propria of the stomach is richly lined with gastric glands.The muscular layer of the cardia gastrica consists of an inner layer of smooth longitudinal muscles and an outer layer of transverse circular muscles.The posterior muscular layers of the stomach body are the inner smooth circular muscle and the outer smooth longitudinal muscle.The pyloric valve consists of a mucosal layer,a submucosal layer and a cricothyroid layer,which increases the length of the stomach and prolongs the digestion time of food in the stomach.The number and height of the mucosal folds in each segment of the intestine gradually decreased from the beginning to the end.The intestine and midgut are the main sites of absorption.The intestine valva consists of a mucosal layer,a submucosal layer and a muscular layer,which serves to prolong the passage of food through the intestine and improve digestion.The liver is divided into two lobes at the front end and later united into a single lobe,which is heart-shaped.The liver is rich in fatty vacuoles.The pancreas is indistinguishable to the naked eye.Histological observations reveal that the pancreas is mainly distributed around the pyloric gastro-intestinal tract,around the bile ducts,around the splenic hilum,and partially diffused in the liver.The above-mentioned structural features indicate that the stomach of O.sinensis increases the volume of the stomach through the pyloric valve and prolongs the digestion time of food in the stomach.The large foregut is an important site of digestion and absorption.The intestine valva prolongs the passage time of the surimi in the intestine and improves the utilisation of the surimi.The liver is primarily used to store nutrients.The development of the digestive system of the O.sinensis is divided into intra-ovarian and post-ovarian.It has a long incubation time,26 days after fertilisation at 17.8 ± 2 °C.The day of fertilization is recorded as 1 DAF(days after fertilization)and the day of emergence at26 DAF,also known as 0 DAH(days after hatching).In embryonic stage.(1)digestive tract development: the digestive tract is already present at 12 DAF.The mouth is a closed cavity.Esophageal lumen not yet formed.The stomach and intestine are not clearly differentiated,being straightforward tubular lumen.The mouth is connected to the outside world,the middle part of the digestive tract expands and divides into a stomach at 15 DAF.The mucosal layer of the posterior segment of the intestine protrudes to form the intestine valve primordium at 16 DAF,which divides the intestine into two anterior and posterior segments.Intestine curves distinctly,and divides the anterior segment of the intestine into three parts at 19 DAF.At this moment,the intestine can be divided into the foregut,midgut,hindgut and rectum.The folds of digestive deepen,empty vesicles appear on the nucleus of the rectum,the anus is connected to the outside at 20 DAF.Formation of pylorus,which lack of gastric glands.(2)Digestive gland development: the liver primordium is present,with indistinct cell boundaries and a few vacuoles.Liver with hepatic blood sinusoids and increased vacuoles at 15 DAF.Hepatocytes with distinct boundaries and increased vacuoles at20 DAF.The pancreas already shows enzymogenic granules at 18 DAF.Before emergence the pancreas is distributed to the mesentery around the hindgut,with abundant enzymogenic granules.The liver and pancreas are obvious at hatching.The organs of the digestive system of O.sinensis are differentiated and formed before hatching.The development after hatching.The O.sinensis are ready to feed at hatching,and the yolk sacs are still visible,entering the mixed nutrition phase.The mucosal,submucosal,muscular and plasma layers are evident in all parts of the digestive tract at 1 day of age after hatching(1DAH).There are empty nuclear vesicles in the foregut,midgut,hindgut and rectum at 2 DAH.Yolk sac is disappearance at 10 DAH,and the fish enter the exogenous nutrition phase.A large amount of pancreatic tissue appeare on the surface of the liver.The annulus muscle is evident in the pyloric valve.The number of mucous cells and mucosal folds are increase,mucosal folds are deepen at 20 DAH.Intestine valve is obvious,and there is no muscular layer.The empty vesicles in the anterior mid-and hindgut nuclei are disappearance at 30 DAH.Gastric glands and mucous cells are increased at 30 DAH.Part of the pancreas is diffused in the liver at 30 DAH.The empty nuclear vesicles remain at 40 DAH.There is a uniquely long intra-ovarian developmental period of O.sinensis.The organs of the digestive system are already differentiated and formed before hatching.The digestive system is already digestive at hatching.The empty nuclear vesicles in foregut,midgut and hindgut are dispearance,it indicates that the digestive system is becoming more functional.It is suggested that the larvae should have enough palatable food when they are hatching.During the stage of gradual improvement of digestive system function,the diet should be mainly digestible.