Effect Of Dietary Carbohydrate Level On Histology Of Liver, Pancreas And Kidney In The Southern Catfish (Silurus Meridionalis Chen)

To study the effect of dietary carbohydrate (CHO) on histological structure in the southern catfish (Silurus meridionalis Chen), using white fishmeal as protein source, corn oil as lipid source, three isonitrogenous and isoenergetic diets containing 0%, 15%, and 30% level of precooked starch were formulated, and were referred to as the control, middle and high CHO diet, respectively. The juvenile southern catfish (20.7±0.5g) were acclimated with the control diet for 15d at 27.5±0.2℃. The morphology of liver, pancreas, and kidney was examined at the 0, 2^nd, 4^th, 8^th, 12^th, and 16^th week.The results were as following: No significant difference was found on hepatocyte densities of the control group irrespective of feeding period, and hepatocyte short diameter, long diameter and area increased with the feeding period lasted. Hepatocyte densities at the middle and high CHO levels at the 8^th, 12^th, and 16^th week were significantly lower than that at the 0 week (P<0.05). And hepatocyte short diameter, long diameter and area were significantly larger than that at the 0 week (P<0.05), no significant difference was found among those at the 8^th, 12^th, and 16^th week. When fed for 4 weeks, a few hepatocytes were swelling, and part of hepatocyte membrane was broken in the middle and high CHO groups compared to the control group. When fed for 8, 12, and 16 weeks, most of the hepatocytes in the fish at the middle and high CHO levels were swelling and more vacuolating than that in the control group, and part of hepatocyte membrane was broken. Parts of pancreatic islets and pancreatic acinuses were broken in the middle and high CHO groups at the 12^th and 16^th week, and a few pancreatic islets were shrinking in the high CHO group. No obvious change was found in the histological structure of kidney among the three groups irrespective of feeding period.The results in this study suggested that the certain level of dietary CHO would impact a nutritional stress of CHO on the carnivorous fish in the sight of histology level. The histological structure of liver was damaged by excess dietary CHO to some extent. As the feeding period lasted, the histology of liver in the fish was damaged severely. When fed for 8 weeks, no change was found in the endocrine and exocrine portion of pancreas in the southern catfish, which should be the histological base the fish fed with dietary CHO could secrete insulin and digestive enzyme normally. No obvious change was found in the morphology of kidney in the southern catfish, and the structure of epithelial cells in the proximal segment was normal, which should be the histological base that the carnivorous fish fed with CHO diet could maintain the function of glucose reabsorption, to avoid to increase the urine glucose excretion.