Effects of dietary carbohydrate levels on growth performance and liver metabolism functions of juvenile tilapia(Oreochromis niloticus)

Abstract

This study was to investigate the effect of dietary carbohydrate levels on juvenile tilapia(Oreochromis niloticus)growth performance and liver metabolism functions.Eight groups of 1 200 tilapias,in triplicate,with initial body weight of(0.36±0.01)g were fed eight experimental diets(similar protein and lipid contents but carbohydrate levels were 10%,15%,20%,25%,30%,35%,40%,45%,respectively).After 7 weeks feeding,the results showed that:(1)dietary carbohydrate level had significant effects on weight gain rate,survival rate,feed conversion ratio and hepato-somatic index(HSI)in tilapia juvenile(P0.05).The growth rate of the fish fed the diet of 35% carbohydrate level was the highest among the treatments,and the feed conversion ratio of the fish fed the diet of 40% carbohydrate level was the lowest.(2)With increasing of dietary carbohydrate,the muscle glycogen and crude fat content gradually increased.However,the glycogen content rose initially and then declined.(3)The activities of serum alanine aminotransferase,aspartate aminotransferase,phosphofructokinase,and the concentrations of serum total protein and total bile acid were all significantly increased with the elevated levels of carbohydrate(P0.05).However,the activities of liver esterase and lipoprotein lipase rose initially and then declined.(4)Liver tissues displayed a few lipid vacuolations in hepatocyte cells at 35%.At the carbohydrate level over 40%,liver histological sections showed a large number of hepatocyte lipid droplets vacuolar degeneration,nuclear migrations and cytoplasm disappearances.The lipid vacuolation areas in liver histological sections basically tallied with the lipid content of the liver,which were consistent with the severity of fatty liver.In conclusion,according to the observation of growth and prevention of late fatty liver disease,the most appropriate proportion of carbohydrate in the fish diet is around 29.10%-35.00%.