Effect of DL-methionine supplementation on the success of almost total replacement of fish meal with soybean meal in diets for hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

This study evaluated the effects of increasing levels of methionine (Met) supplementation on the success of almost total replacement of fish meal (FM) with soybean meal (SBM) in diets for hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus). Fish were fed for 70 days a FM-based diet (Diet1-positive control) or SBM-based diets supplemented with graded levels of DL-methionine (Diet2 to Diet7). Contrast in dietary Met, concentration was created by supplementing Diet2-negative control with 1.2 (Diet3), 2.4 (Diet4), 3.6 (Diet5), 4.8 (Diet6) or 6.0 g kg−1 (Diet7) of DL-Met. Specific growth rate (SGR), feed conversion ratio (FCR), and protein gain and retention efficiency (PER) improved significantly with increasing levels of dietary DL-Met supplementation. Moreover, nonlinear regression analysis of the effects of supplementing SBM-based diet with graded levels of DL-Met indicated that a dietary Met + Cys level of 15.7 and 12.5 g kg−1 diet (as fed) was required to reach 95% of maximum weight and protein gain, respectively. Supplementation of SBM-based diet with graded levels of DL-Met proved an effective strategy in reducing FM content in practical diets for hybrid tilapia. Data also indicate that adjustment of dietary formulas according to currently recommended Met or Met + Cys dietary concentrations is probably limiting maximum growth potential of hybrid tilapia.