Studies On The Development Of Digestive System And The Effect On Digestive Enzymes Of Different Diets And Environments On Bleeker, Erythroculter Ilishaeformis

The development of the digestive system of bleeker was reported in this research. Since diet and environment will affect the growth of fish,investigations were made to reveal the effect of different diets and environments on the growth of juvenile bleeker and digestive enzymes of juvenile and adult fish.The purpose of this research was to provide more basic information for post-embryonic development of the digestive system of fish.It also gave references to the culture of carnivorous fish with artificial diets and to optimizing of the artificial diets.Paraffin section was used to observe the histological change of the development of the digestive system of bleeker.It was found that the digestive tract had not differentiated at hatching.The fish larvae utilized the nutrient during the yolk sac to maintain its growth in the first few days,which means that the fish larvae werein the stage of endogenous feeding.The digestive tract is an undifferentiated tube at dorsal side of the yolk sac at ldah(day after hatching).The mouth of fish larvae opened at 2dah,while the larva couldn't ingest exogenous food.Enterocytes could be found at 3dah.The fish larvae began exogenous feeding at 5dah,while the yolk sac was absolutely exhausted.The development of liver was observed at 8dah and the goblet cells in intestine epithelium was found at 16dah.The activities of tryptase and amylase were detected at hatching.On the contrary, lipase activity couldn't be found.The activity of AKP kept increasing after hatching. The activities of tryptase,amylase and AKP decreased at 4dah and then increased,which were caused by the conversion to exogenous feeding.The total length of fish larvae fed by artificial feed(test group)was significantly lower(p＜0.05)than that of fish larvae fed by Cladocera(control group).It shew that the artificial feed affected the growth of fish larvae.The activity of tryptase of both groups increased in 10 days after feeding and then decreased.The activity of amylase of test group was significantly lower(p＜0.05)than that of control group,except at 30 days after feeding.There was no significant difference between the activities of AKP in both groups,except at 6days after feeding.The activity of AKP of control group decreased at 15days after feeding,while that of test group decreased at 30 days after feeding.The fish larvae of test group had more goblet cells in intestine epithelium than that of control group,which indicated that the feeding of artificial feed affected the cell distribution and the structure of intestine.Four groups of bleeker which are wild group(WG)harvested from Taihu lake, artificial group(AG)cultured with compound feed,with trash fish(TG)and no extra adding feed(NG)in ponds respectively,were collected.The experiment was conducted to investigate the effect of different type culture condition and diets on the three kinds of digestive enzymes such as protease,amylase and lipase.The results showed that the activities of protease,amylase and lipase in intestine were much higher than that in hepatopancreas(p＜0.05).The activity of protease was in descent ranged as:NG＞AG＞TG＞WG.The insufficient food at intervals may result in the lower activity of protease in WG.The activities of protease in foregut and hindgut of NG were 3.1-1.8 and 3.2-1.8 times as that in the same sector comparing with the other three groups.The activities of protease in AG were in ascent ranged as along with the different gut sector,contrary to the activities of protease in TG.It may result from the texture and moisture content of different feeds because the artificial feed is more firm than that of trash fish.In hepatopancreas,the activities of protease was significantly lower in TG than that in AG(p＜0.05).The activities of amylase in hepatopancreas were declined as follow as NG＞TG＞WG＞AG.In whole gut,except in hindgut,the activity of amylase was highest in TG and lowest in WG..The activity of lipase was in descent ranged as:AG＞WG＞TG＞NG,but there was no significant difference among the four groups except for the activity in hindgut.The lipase activity of hindgut in TG was significantly lower than that in AG and NG..It has shown that different types of culture condition and diets had less influence on lipase activity comparing with that of protease in bleeker.