A comparative study on the tolerance of tilapia(Oreochromis niloticus)to high carbohydrate and high lipid diets

A 12-wk trial was conducted to compare the tolerance of tilapia to high carbohydrate and high lipid diets.Three isonitrogenous and isoenergetic diets,whose carbohydrate and lipid levels were the following:35.0%and 8%(control),44.2%and 4%(D1,high carbohydrate),and 25.8%and 12%(D2,high lipid),respectively.Three hundred tilapias(27±0.11 g)were fed the diets for 10 wk(4 replicates per group);72 fish from the D1 group were continually fed the D1(D1D1)and 72 fish from the D2 were continually fed the D2(D2D2)diet for 2 wk(3 replicates each group)to evaluate the tilapia's capacity to tolerate high carbohydrate and high lipid diets,respectively.Another 36 fish from D1 group were continually fed D2(D1D2)for comparison with D1D1 and D2D2 groups.In phase 1,hepatosomatic index,liver triglycerides(TG),glucose tolerance(GT)and crude protein in the whole body in D1 group were higher than those in D2 group(P<0.05).During phase 2,D1D1 group had lower feed intake and weight gain,as well as lower serum total protein and albumin than that of D2D2 group(P<0.05),while its liver glycogen was significantly higher than that in D1D2 and D2D2 groups(P<0.05).Moreover,serum glucose and GT were higher in D1D1 and D1D2 groups than those in D2D2 group(P<0.05).By contrast,D2D2 group had significantly higher intraperitoneal fat,subcutaneous adipose tissue(SCAT)and liver TG than those in D1D1 group(P<0.05).The mRNA expression of brain npy,hepatic nrf2,gst1 and hepatic transcriptomic data showed that immune-related genes(gama,mrc2,mhc2 and cd163),were downregulated in D1D1 group compared to D2D2 and D1D2 groups.Taken together:1)tilapia have higher tolerance to a high lipid diet than high carbohydrate diet;2)despite retention of glucose tolerance,the continuous feeding of D1 diet impaired tilapia's appetite,weight gain rate and host immune response;3)specific distri-bution of fat in intraperitoneal regions,SCAT and liver may be a risk-avoidance strategy in tilapia in response to a continuous D2 diet.