| In the present study,we focused on the study of juvenile Sillago sihama.It was studied in terms of the optimum protein and lipid levels of the diet,and the replacement of fish meal by low-gossypol cottonseed meal.The main findings were twofold as follows:1.Casein,white fish meal and wheat gluten were used as protein sources and fish oil and soy lecithin as fat sources.Four protein levels(40%,45%,50% and 55%)and three lipid levels(8%,10% and 12%)were formulated for complete crossover experiments,for a total of 12 diets.Experiments were conducted with 1080 juvenile grouper with an average weight of 0.83 ± 0.01 g.Three replicates of 30 fish in one replicate were selected for each group,and the experiment period was 8 weeks.Result:Weight gain rate(WG),specific growth rate(SGR)and protein efficiency ratio(PER)were significantly higher in the 50% protein level(P50)group compared to the 40% protein level(P40)group.However,a decreasing trend in WG was observed when the diet protein level was 55%(P55).WG was significantly higher(P<0.05)in the lipid level 12%(L12)group than in the lipid level 8%(L8)group.At the same time,lipid levels above 10% in the diet significantly reduced whole-body moisture content;significantly increased condition factor(CF),hepatosomatic index(HSI)and viscerosomatic index(VSI);and significantly increased whole-body crude lipid levels(P<0.05).Excessive energy in the diet resulted in a decrease in the daily feed intake(DFI)of Sillago sihama.According to WG,the quadratic regression model fit yielded a diet optimum protein level of 48.42%(dry matter)when the lipid level was 10%;and 48.53% when the lipid level was 12%.Liver glutamic-pyruvic transaminase(GPT)and glutamic-oxalacetic transaminase(GOT)activities increased with increasing diet protein levels,and glutamate dehydrogenase(GDH)activities were significantly higher in the high-protein diet group(50% and 55%)than in the low-protein diet group(40% and 45%)(P<0.05).Lipoprotein lipase(LPL)activity was significantly higher in the high lipid level group(10% and 12%)than in the low lipid level group(8%)(P<0.05).Fatty acid synthase(FAS)activity decreased with the increase in diet lipid level.Diet lipid level significantly up-regulated the expression level of insulin-like growth factor1(igf-1)gene(P<0.05).The expression level of target of rapamycin(tor)gene in the liver increased with increasing diet protein level at 45% to 50% protein level,but decreased at 55%diet protein level and was significantly lower than that of the 50% protein level group(P<0.05).In conclusion,the results of this study show that the optimum protein level for the diet of Sillago sihama is 48% and the lipid level is 10%-12% for the best growth.2.White fish meal(FM),wheat gluten meal,Soybean protein concentrate and lowgossypol cottonseed meal(LCSM)were used as protein sources,and fish oil and soy lecithin were used as lipid sources.LCSM replacement levels were formulated as 0(R0,control,containing 550.0 g/kg FM),16%(R16,88.5 g/kg LCSM and 461.5 g/kg FM),32%(R32,177.0 g/kg LCSM and 373.0 g/kg FM),48%(R48,265.5 g/ kg LCSM and 284.5 g/kg FM)and 64%(R64,354.0 g/kg LCSM and 196.0 g/kg FM)of the five isonitrogenous and isolipidic diets.The experiment was conducted with 450 juveniles Sillago sihama weighing5.8 ± 0.58 g on average,with three replicates of 30 fish per group and an 8-week experiment period.Result:WG and SGR were significantly higher in the R0 and R16 groups than in the R48 and R64 groups(P<0.05).In contrast to whole-body crude protein,whole-body moisture increased with increasing FM replacement levels(P<0.05).Intestinal amylase(ASM)activity increased significantly(P<0.05)and intestinal trypsin(TRP)activity decreased significantly(P<0.05)as the level of LCSM in the diet increased.The increase in diet LCSM upregulated the expression of intestinal tumor necrosis factor-α(tnf-α),nuclear factor kappalight-chain-enhancer of activated B cells(nf-κb)and interleukin-β(il-1β),but downregulated the expression of tight junction protein zo-1(zo-1),transforming growth factor β-3(tgf-β3)and interleukin 10(il-10).Histological analysis showed that morphological damage in the midgut gradually increased with increasing levels of fish meal replacement.In terms of liver indicators,liver malondialdehyde(MDA)content,alkaline phosphatase(AKP)activity and reactive oxygen species(ROS)concentrations peaked in the R0 group and were significantly higher than in the R32,R48 and R64 groups.Liver catalase(CAT),glutathione peroxidase(GSH-Px),total superoxide dismutase(T-SOD),lysozyme(LYZ)activity,immunoglobulin M(IgM)concentration and total antioxidant capacity(T-AOC)levels all achieved maximum values in the R32 group.With the increase of LCSM level in the diet,the expression level of liver il-10 was upregulated,while the expression levels of liver tumor necrosis factor-α(tnf-α),target of rapamycin(tor),insulin-like growth factor 1(igf-1)and transforming growth factor β-3(tgf-β3)were downregulated.The expression levels of liver nf-κb and il-1β were not affected by the level of diet LCSM.Some genes of complement component 3(c3),complement factor H(cfh),complement factor B(cfb),and mbl-associated serine protease 1(masp1)in the complement pathway were significantly upregulated(P<0.05)when the fish meal replacement level reached 32%.In summary,16%(88.5 g/kg)of fishmeal can be replaced with LCSM,with excessive replacement levels causing intestinal damage,but with less effect on liver immunity. |
