HISTOLOGICAL AND ULTRASTRUCTURAL STUDIES OF THE STOMACH AND INTESTINE IN LARVAE OF YELLOW CATFISH PELTEOBAGRUS FULVIDRACO

Yellow catfish(Pelteobagrus fulvidraco) is an important commercial freshwater species in China.Due to its high market value,the culture of this species has increased rapidly in recent years.However,larvae rearing became a major bottleneck because of its high mortality.In order to enhance the success of larvae rearing of P.fulvidraco,we need to know the ontogeny of its digestive system thoroughly.The purpose of this study was to understand the morphological structure and the ultrastructure of digestive tract during the ontogeny of P.fulvidraco.We hope that this information would provide fundamental knowledge for larvae rearing management for this species.The histological and ultrastructural characteristic studies of the stomach and intestine of yellow catfish were carried out from hatching(0d after hatching(DAH)) until 35 DAH.Larvae were hatched from artificially spawned broodstock and maintained in the laboratory(water temperature was 23-25℃).They were fed with zooplankton from 3 to 17 DAH,adding zoobenthos from 10 DAH,and only zoobenthos from 18 to 35 DAH.Development of the digestive tract in yellow catfish followed the general pattern described for other species.At hatching,it consisted of an undifferentiated straight tube laying over the yolk sac.The digestive tract was differentiated into buccopharynx,esophagus,initial stomach,and intestine by 2 DAH.The intestine became differentiated into anterior and posterior regions separated by a valve at 3 DAH.The gastric gland in cardiac stomach appeared at 3 DAH,the same time at the first feeding.In ultrastructure,oxynticopeptic cell contained pepsinogenic granules and abundant tubulovesicular systems at 3 DAH.The abundant visible tubulovesicular systems suggested that oxynticopeptic cell was still in rest phase with little hydrogen chloride(HCl) secreted at the first appearance time.As larvae grew,more pepsinogenic granules but less tubulovesicular systems were found in oxynticopeptic cell.There were abundant pepsinogenic granules but little tubulovesicular systems in gastric gland cell at 25 DAH.The epithelial absorptive cell of the anterior and posterior intestinal segment showed electron-opaque lipid droplets and heavy pinocytosis at 3 DAH.Heavy pinocytosis was observed in the posterior intestine between 3 and 25 DAH.The results of this study suggested that the development of digestive tract of yellow catfish larva was functional rapidly,but incomplete.Pinocytotic absorption and intracellular digestion of proteins can compensate for this incomplete extracellular digestion.It is suggested feeding management strategy in line with the physiological function development process in order to effectively increase the survival rate of larva and juvenile of yellow catfish.