| Samples of the bagrid catfish Mystus n;acroplerus(Bleeker), including pro-larvae, post-larvae, juvenile fish were obtained by artificial propagation of spawners collected from the Beibei-Hechuan section of the Jialing River from the end of June to the middle of July 1 988.Young and adult were collected from the haling River too,from Octorber 2000 to May 2001 With slice technology and light microscope,the postembryonic development characteristics of the digestive system in A-f macroplerus were observed for the first time.The results are as follows:According to the histological development characteristics of M n;acroperus,the structure and function of the digestive system developed gradually during the development stages from the pro-lan'al,post-larval to juvenile period and well developed in young fish.As in other teleost species,the esophagus,stomach, intestine,liver and pancreas of M rnacropterus began to develop during the pro-larval period,then became mature gradually,different from Odontohutis po(amophila whose digestive system bad well developed during the embryonic stage.The inner longitudinal muscle fiber of the oesophagus was one part of its submucosa,instead of muscutaris. The muscularis,consisting of inner circular and outer longitudinal muscles,were composed of striated muscle fibers.The outer longitudinal muscle was not continuous and poorly develped.Obvious histological differences were observed in the anterior and posterior oesophagus.For example,the anterior oesophagus had taste buds and developed inner longitudinal muscle fibers;the posterior oesophagus had no taste buds and poorly developed inner longitudinal muscle fibers, but had more mucous cells.The first differentiation of gastric glands had occurred at the end of endogenous feeding (day 5 after hatching),which was in relation to the transition from endogenous to exogenous feeding and was helpful to ingest exogenous food.The gastric glands were composed of a single secretory cell type and increased in size and number during larval and juvenile periods of development The stomach could be divided into three parts:an anterior glandular region(cardia),an intermediate glandular region (lbndus) and a posterior non-glandular region(pylorus).At the stomach—oesophagus jun3tion,some inner circular muscles of the cardiac part(or cardia)of the stomach were composed of striated muscle fibers.Possibly owed to being not well-developed,the sUia was not typical during the larval peiiod Although the pyloric part(or pylorus)of the stomach was devoid of glands, it had the thickest27muscularis and deepest plicamucosa among the three parts, one ftinction of which is possibly to enable mechanical digestion.During the larval period the mitosis of the stomach and intestine cells led ,to multinucleated syncytia and plicaniucosa.The brush borders of the epithelial cells could be detected at 1 --3 days after hatching and were well-developed at 7—8 days post-hatch,which was a compensation to the immature histological structures of the intestine during early period.Afler pro-larval period,the vacuolus appeared in the epithelial cells,which were vacuolus of fat absorbed through the brush borders and their numbers increased with the larval development. The digestive tract muscularis,particulary longitudinal muscles,was not well developed,and only provided very low mechanical digestive capacities during the larval stage.The liver contained abundant hepatic sinusoids that was helpftul to the accumlation of nutritious material and the development of hepatic cells.At day 5 post-hatch,the posterior part of the liver started to accumlate lipids and the adult had abundant fat vacuoles,which was possibly related to its carnivorous habits.In Mmacropieru~the pancreas is a difiüse gland,distnbuted on the border of the liver and on the surface of peritonwm,and sunounding the gall bladder,intestine and spleen.Some pancreatic tissue even extended into the liver with hepatic vein.The pancreas consists of two typical portions,the tubular exocrin... |
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