Title: Lysine optimization of a commercial fishmeal-free diet for hybrid striped bass (Morone chrysops x M. saxatilis) Authors
Submitted to: Book of Abstracts Aquaculture America
Publication Type: Abstract Only
Publication Acceptance Date: January 9, 2013
Publication Date: February 21, 2013
Citation: Rawles, S.D., Fuller, S.A., Beck, B.H., Gaylord, G., Barrows, F., Mcentire, M.E. 2013. Lysine optimization of a commercial fishmeal-free diet for hybrid striped bass (Morone chrysops x M. saxatilis)[abstract]. Book of Abstracts Aquaculture America 2013: Strike a Chord for Sustainable Aquaculture, February 21-25, 2013, Nashville, Tennessee. p.889. Technical Abstract: Substitution of fishmeal with alternate proteins in aquafeeds often results in dietary imbalances of first-limiting essential amino acids (EAA) and poorer fish performance. This 12-week growth trial was undertaken to test the hypothesis that ideal protein theory accurately predicts first-limiting amino acids and the optimum lysine level for a fishmeal-free, commercial-grade diet formulated for hybrid striped bass (HSB). A negative control diet (D1) based on soybean (45%), corn gluten (10%), and poultry by-product (13%) meals was formulated on an ideal basis to contain 16% lipid, 40% crude protein (CP), 36% digestible protein (DP) and 1.8% LYS from intact sources based on in-house digestibility data. MET and THR were then added at levels equivalent to 40% HSB muscle to form a basal diet (D2) containing 42% CP and 37% DP. The basal formula was fortified with seven levels (2.2, 2.8, 3.1, 3.4, 3.5, 5.1, 6.4 g/g diet) of LYS at the expense of wheat starch to form additional test diets (D3-D9) that bracketed the predicted ideal lysine requirement (3.5g/g diet) for this formulation. The diets were extruded to mimic commercial-grade fish feed. Juvenile fish (118 g initial weight) were stocked (35 fish/tank; 3 tanks/diet) in 27 x 650-L round tanks supplied with flow-through well water and ample aeration, and fed daily to satiation until the highest weight gains achieved 200%. Response data were subjected to polynomial and exponential regression and the best model per response selected based on the lowest error (MSE) and p-values < or = 0.05, and the highest adjusted R2 > or = 0.25. Selected models were used to derive dietary lysine levels required to reach 95% (R95) or 99% (R99) of the minimum or maximum y-response. Mean final fish weights (328–369g) increased linearly with increasing LYS in the diet. Weight gain (%), average daily feed intake (1.42-1.7%), and feed efficiencies (FE) at 4-, 8-, and 12-week intervals were well-modeled by cubic functions that yielded fairly consistent R95 and R99 dietary levels of about 2.4 and 4.3g LYS/g diet, respectively. These values evenly bracket the predicted ideal LYS level. A slightly higher LYS requirement was found for optimum FE at 4 weeks and smaller fish, as opposed to 8 or 12 weeks and larger fish. Whole body composition was unresponsive to dietary LYS level; however, liver size (HSI), body fat (IPF), and muscle ratio were consistent with cubic functions. Higher dietary LYS was required to minimize HSI (4.8 to 5.2 g LYS/g diet) than to minimize IPF (2.5 to 3.1 g LYS /g diet) or maximize muscle ratio (1.8 to 3.9 g LYS/g diet). Whole body protein, lipid, energy, and EAA retention efficiencies were also consistent with cubic functions that generally confirmed the predicted ideal LYS level with notable exceptions. Retention of LYS decreased exponentially with increasing diet LYS, whereas, MET retention decreased in a slow linear fashion, corroborating that MET was first-limiting in the diet formula as predicted. Retention efficiencies of THR and branched-chain amino acids (LEU, ISL, VAL) were optimized at higher LYS concentrations (3.9-4.5 g/g diet) than those required to maximize production parameters. Protein accretion (g/fish/d) responded quadratically to LYS intake predicting maximum deposition at 0.10 to 0.16 g LYS/fish/d. Histological assessment of intestines in fish fed these high-soybean meal test diets did not reveal any lesions associated with enteritis for any diet and overall normal intestinal morphology was observed in all fish sampled.