Dietary Crystalline DL-Methionine Supplementation of Oilseed Meal-Based Diets: Effects on Growth and Feed Utilization of Juvenile Nile Tilapia (Oreochromis niloticus L.)

Aim: This study evaluated the effect of dietary DL-methionine supplementation of diets containing mixtures of oilseed meals (i.e. soybean meal, SBM; cottonseed meal, CSM and groundnut cake, GNC) on the growth and feed utilization of Nile tilapia (Oreochromis niloticus L.) of mean initial weight 5.48±0.20g.
Study Design and Methodology: Five isonitrogenous (320g kg-1), isolipidic (100g kg-1) and isoenergetic (18KJ g-1) test diets were formulated in which different mixture combinations of oilseed meal (i.e. EQ50, SBM50, CSM50 and GNC50) proteins enriched with crystalline DL-Methionine (0.5%) replaced fish meal (FM) protein at 50%. The control diet had FM as the major protein source. Fish were fed to satiation from the beginning and later fixed at 4% body weight per day and the study lasted for 56 days. The growth experiment was conducted in plastic tanks in a recirculation system with each dietary treatment in triplicate.
Results: Growth and feed utilization of fish fed the control diet were significantly higher (P<0.05) than for all the oilseed meal-based diets (supplemented with methionine). There were no significant differences in whole-body protein, moisture, lipid and energy contents among diets, with the exception of Diet 4 which had lower protein content. The cost analysis also showed that the control diet was the most cost effective.
Conclusion: Results in the present study demonstrated that utilization of crystalline DL-methionine (0.5%) by Nile tilapia was not effective in improving the growth, feed utilization and cost effectiveness of the diets containing oilseed meal mixtures compared with the fish meal based diet.