Effects Of Dietary Lipid And Protein Levels On Growth, Body Composition, Non-specific Immunity And Hematological Parameters Of Largemouth Bass (Micropterus Salmoides)

An88-day feeding test was conducted to estimate therequirements of dietary lipid and protein in largemouth bass with aninitial body weight of (10.06±0.02)g. Eight diets (D1-D8) used fishmeal, spray-dried blood meal and so on as primary protein sources,then the essential amino acid profile of the diets simulated the profilein largemouth bass muscle protein by adding zein-coated crystallineamino acid mixture. The protein ingredients used in the diets werechanged propotionally in order to keep the profile constant. Soybeanoil was used as a main lipid souce in the diets, and fish oil was addedto compensate the amount of fish oil caused by the reduction of fishmeal. The diets were formulated with varying lipid to protein(LIP/PRO, w/w) ratios ranging from0.17to0.84. From D1to D8,dietary lipid levels were increased from9.0%to26.5%resulting in anincrease in dietary gross energy, while dietary protein levels weredecreased from52.0%to31.0%by reducing protein ingredientsproportionally. Each diet was assigned randomly to triplicate tanks,and30fish were stocked in each tank. All the tanks were connected to an indoor aerated recirculating freshwater system. Fish were fed byhand to apparent satiation twice daily (08:00and16:00). During theexperimental period, water temperature was maintained at (28±1)℃and dissolved oxygen content kept nearly saturated. The natural lightcycle was adopted.The results of this study were as follows:The growth performance and feed utilization were significantlyaffected by the dietary lipid and protein levels. The survival rates weresignificantly higher in fish fed D1and D2with higher protein levels thanthose in fish fed D5-D8with lower protein levels (P <0.05). The specificgrowth rate, feed efficiency ratio and lipid deposition rate of D2-fed fishwere the highest, but those of fish fed the other diets with a higherLIP/PRO ratio showed a significant downward tendency (P <0.05). Theprotein efficiency ratio was significantly higher in fish fed D3-D5,compared with the fish fed D1and D8(P <0.05). The protein depositionrates between D2-, D3-and D4-fed fish were not significantly different(P>0.05), but significantly higher than those with the other treatments (P<0.05).Excessive dietary lipid had a significant effect on the bodycomposition with increased body lipid deposition (P <0.05), while it hadless effect on muscle lipid content than on visceral lipid content.Hepatosomatic indexes (HSI) in fish fed D7-D8were significantly higher than in the fish fed D1-D3(P <0.05). The viscerosomatic index (VSI)was significantly higher in D8-fed fish, compared with other treatments(P <0.05). The condition factor of D2-fed fish was significantly higherthan in fish fed D3-D8(P <0.05).Dietary protein digestibility coefficient and dietary lipid digestibilitycoefficient with D2-fed fish were the highest. Although no significantdifference in dietary energy digestibility coefficient occurred among thefish fed D1-D4(P>0.05), the coefficients were significantly higher thanthose with other treatments (P <0.05).Dietary lipid and protein levels also significantly affected thenon-special immunity parameters of serum lysozyme activity and serumclassical complement pathway (CH50) activity as well as respiratory burstactivity of the head kidney leukocytes (P <0.05). The highest activity oflysozyme, CH50activity and respiratory burst of head kidney leukocytesoccurred in D4-, D2-and D2-fed fish, respectively.There are significant differences in the haematological paramentersof red blood cell count, haemoglobin concentration (Hb) and haematocrit(Hct) in fish fed diets with different lipid and protein levels (P <0.05).The red blood cell counts between D2and D3fed fish showed nosignificant difference (P>0.05), but were significantly higher than thosewith the other treatments (P <0.05). The haematocrit (Hct) of D2-fed fishwas significantly higher than in the fish fed D1and D4-D8(P <0.05). The haemoglobin concentrations (Hb) in fish D1-D4were significantlyhigher than those in the other treatments (P <0.05).Based on the results it could be concluded that the largemouth bassrequires a high level of dietary protein. The growth performance, bodycomposition and non-specific immunity were affected by dietary lipid andprotein levels to a different extent. In addition, an excess of dietary lipidwould inhibit the digestion of dietary protein. Thus, protein-sparing effectof dietary lipid is limited in this fish species. According to a one-wayANOVA, the optimal dietary protein and lipid levels for largemouth basswere49.30%and11.50%, respectively. Using a second-order polynomialregression analysis, the optimum dietary protein, lipid and lipid to proteinratio (L/P) in diets for largemouth bass were estimated based on thespecific growth rate (SGR) and protein deposition rate (PDR). When SGRwas the highest, the optimum dietary protein, lipid and L/P wereestimated to be48.20%,12.44%and0.26. When PDR was the highest,the optimum dietary protein, lipid and L/P were estimated to be46.42%,13.96%and0.30. A quadratic regression analysis of PDR against dietaryprotein to energy ratio (P/E) indicated a similar result that the optimumdietary P/E, protein, lipid and L/P requirements of largemouth bass were23.72mg/KJ,46.16%,14.18%and0.31, respectively. It could berecommended to maintain dietary protein and lipid levels within46%-49%,11.5%-14%, respectively, in the practical feed for largemouth bass.