Effect Of Dietary Lipid Levels And Sources On Growth Performance,Body Compositions And Feed Utilization Of Juvenile Spotted Knifejaw Oplegnathus Punctatus

Lipid,as one of the main nutrient elements in aquatic feed,is of vital importance to the growth,development and reproduction of aquatic animals.Therefore,for each aquatic animal,exploring its requirement for lipid nutrition is conducive to promoting the development of high-efficiency specific formula feed,so as to save the breeding cost and improve the breeding income.So,this study was conducted to explore the effects of dietary lipid level and lipid sources on growth,feed utilization and body compositions of spotted knifejaw Oplegnathus punctatus with two experiments:Experiment 1: Effects of different feed fat levels on growth,feed utilization and body composition of juvenile O.punctatus.In this experiment,6 diets with different lipid levels(2.30%,6.31%,8.98%,12.93%,16.08% and 18.99%)were formulated and fed to juvenile O.punctatus for 8 weeks.After the feeding experiment,the weight gain(WG)and specific growth rate(SGR)significantly elevated with raising the dietary lipid level to 12.93%,and then deteriorated when dietary lipid further increased(P < 0.05).The tendencies of feed efficiency(FE),protein efficiency ratio(PER),nitrogen retention(NR)and energy retention(ER)were consistent with the growth performance(P < 0.05).The lipid retention(LR)significantly deteriorated with dietary lipid increasing(P < 0.05).The fish consuming 2.30% and 6.31% lipid diets had significantly elevated hepatosomatic index(HIS)(P < 0.05).The intraperitoneal fat ratio(IPF)was increased when dietary lipid elevated(P < 0.05).The elevation of dietary lipid levels significantly increased the lipid concentrations in the whole body,dorsal muscle and liver(P < 0.05).The liver glycogen deposition in 2.30% dietary lipid treatment was highest(P < 0.05).The fish consumed 12.93% lipid diet had the highest serum protein concentration(P < 0.05).The lowest total cholesterol(TC)content in the serum was detected in 2.30% dietary lipid treatment(P < 0.05).The fish consumed 2.30% or 18.99% lipid diet obtained elevated serum AST and ALT activities(P < 0.05).The regression analysis in two slope broken-line mode based on WG and FE indicated that 10.46-12.71% lipid level in diet was optimal for juvenile O.punctatus.Experiment 2: Effects of different feed fat sources on growth,feed utilization and body composition of juvenile O.punctatus.In this experiment,4 iso-nitrogenous and sio-lipidic diets were formulated with fish oil,soybean oil,rapeseed oil and linseed oil as lipid source respectively and fed to juvenile O.punctatus for 8 weeks.The results of the experiment showed that WG and SGR of juvenile O.punctatus fed diets with fish oil and linseed oil were significantly higher than those fed diets with soybean oil and rapeseed oil(P < 0.05).FE in fish oil group and linseed oil group was significantly higher than that in soybean oil group and rapeseed oil group(P < 0.05).Linseed oil group showed the highest PER value and it was significantly higher than that in soybean oil group and rapeseed oil group(P < 0.05).The viscerosomatic index(VSI)and HSI of juvenile O.punctatus fed diet with soybean oil were significantly higher than those of other treatment groups(P < 0.05).The fish in linseed oil group obtained the highest condition factor(CF),which was significantly higher than that in rapeseed oil group and soybean oil group,but there was no significant difference with fish oil group(P < 0.05).There was no significant difference in IPF among all groups(P < 0.05).The liver lipid content of juvenile O.punctatus in soybean oil group was significantly higher than that of linseed oil group,but there was no significant difference with rapeseed oil group and fish oil group(P < 0.05).There were no significant differences in the composition of whole fish and muscle as well as liver water and protein between different treatment groups(P > 0.05).The results of tissue fatty acid composition analysis showed that the total SFA content in the dorsal muscle and liver of juvenile O.punctatus in fish oil group was higher than that in other groups(P < 0.05).The total MUFA content in dorsal muscle and liver of fish fed rapeseed oil diet was higher than that of fish fed other diets(P < 0.05).The total n-3 PUFA content in dorsal muscle and liver of fish fed linseed oil diet was significantly higher than that in fish oil group,while the total n-3 PUFA content in dorsal muscle and liver of fish fed soybean oil diet and rapeseed oil diet was significantly lower than that in the other groups(P < 0.05).The highest total n-6 PUFA content in the dorsal muscle and liver was observed in the fish fed with soybean oil diet,while the lowest was detected in fish oil group(P < 0.05).The ratio of n-3/n-6PUFA in dorsal muscle and liver of fish fed fish oil and linseed oil diets was significantly higher than that of the other groups(P < 0.05).The DHA and EPA contents in muscle of fish fed fish oil diet were significantly higher than those of other groups(P < 0.05).The EPA content in the liver of fish fed fish oil and linseed oil feed was significantly higher than that of the other groups(P < 0.05).The DHA content in the liver of fish fed fish oil feed was the highest and significantly higher than that of fish fed soybean oil and rapeseed oil diets,but there was no significant difference between the fish oil and linseed oil groups.According to the results of the experiment,linseed oil can replace fish oil as a fat source in the formula diet for juvenile O.punctatus,without effect on growth and feed utilization,but soybean oil and rapeseed oil are not suitable to add in the formula diet as a single lipid source.