Effects Of Dietary Lipid Levels On Growth Performance, Nutritional Components And Activities Of Digestive Enzymes Of Siganus Guttatus

Lipid is the main nutrient elements in aquatic animals and Its content in the feedshould be appropriate. This paper studied the enzymology and hematological of Siganusguttatus cultured in different salinities. Siganus guttatus was chosen to be researched,mainly in optimum dietary protein requirement, animal protein to plant protein ratio anddietary protein to energy ratio in this study. For the production of Siganus guttatus feed,providing the nutrient composition of fat content.1、Effects of dietary lipid levels on growth performance and body composition ofSiganus guttatusA growth trial was conducted to evaluate the effect of dietary lipid level on growthperformance and body composition of Siganus guttatus. Six isonitrogenous diets withincreasing lipid levels of4.16%(L1),7.42%(L2),10.68%(L3),14.20%(L4),16.56%(L5),19.62%(L6) were fed to duplicate groups of fish28.09±0.60g for8weeks and weightgain was recorded. At the end of the feeding experiment, fish fed with10.68%lipid dietand14.20%lipid diet showed optimal growth performance (P<0.05). Lipid content ofwhole body, muscle and liver increased in parallel with the increase in dietary lipid levels.The whole body protein content of L1and L6were the lowest, while there were nosignificant differences with other four groups (P>0.05). Protein content, moisture content,and ash content of the muscle were not significantly affected by dietary lipid level.Moisture content of liver decreased with the increase in dietary lipid levels. Inconsidering these results, in this study, it was concluded that the optimum dietary lipidrequirement for Siganus guttatus was10.68%~14.20%. Based on a second-orderpolynomial regression analysis of lipid level against weight gain rate, the optimumdietary lipid level for Siganus guttatus was13.94%.2、Effects of dietary lipid level on fat deposition and fatty acid composition ofSiganus guttatus The conceputual design of raising was the same as that of the one. At the end of thefeeding experiment, fat content of muscle, liver and mesentery increased in parallel withan increase in dietary lipid level. When dietary lipid level raising from L1to L3, the fatcontent of liver increased significantly, but the mesentery fat content is stable after L2.The partial physique indices were influenced by dietary lipid level, especially mesentericfat index (MFI). The fatty acid composition of fish reflected fatty acid composition in theexperimental diets, and the C22:6n-3(DHA) was stored more easily than C20:5n-3(EPA)in Siganus guttatus.Comparisons were made between wild and experimental S.guttatus. Results showthat there are larger proportions of saturated fatty acids (SFA) in the wild fish(P<0.05).The C12:0content in the wild group are significantly higher than each experimentalgroup (P<0.05), and C16:0content are significantly higher than all experimental groupsexcept L1and L2(P<0.05). On muscle monounsaturated fatty acid (MUFA), no obviousdifferences are found between wild and experimental S.guttatus (P>0.05). The wild fishand L1group have similar proportion of polyunsaturated fatty acids (PUFA)(P>0.05),but eieosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and n-3/n-6coefficient ofexperimental groups were significantly(P<0.05) higher than wild group which has higherproportion of C20:4n-6.3、Effects of dietary lipid levels on activities of digestive enzymes and bloodbiochemical index of Siganus guttatusThe conceputual design of raising was the same as that of the one. The resultsshowed that the protease activities of stomach were the highest from L2to L4. Theactivity of protease in the pyloric caeca of L2and L3were significantly higher than thoseof other groups (P<0.05), while the highest activities of midgut proteinase appeared at L4(P<0.05). The lipase activity of intestinal tract was increased at first and then decreased,while the lipase activities of stomach, pyloric caeca and liver had not signifcantlychanged between treatments (P>0.05). The activity of amylase activities in the pyloriccaeca of L3and L4were significantly higher than those of other groups (P<0.05), but theamylase activities of foregut and midgut were declined. The cholesterol concentrationincreased with the increase of dietary lipid level. The levels of alanine aminotransferase(ALT) and aspartate aminotransferase (AST) at L3, L4and L5were significantly lowerthan other groups (P<0.05). Alkaline phosphatase (ALP) in serum increased with theincrease of dietary lipid level. Blood urea (UREA) content at L3, L4and L5were significantly lower than those of L1, L2and L6.