Performance of sunshine bass fed soybean-meal-based diets supplemented with different methionine compounds

Practical diets that contain high levels of plant proteins often require supplementation with methionine to satisfy the total sulfur amino acid requirements of animals. The present study was designed to evaluate L-methionine, DL-methionine, N-acetyl-DL-methionine (acetylmethionine), and or-methionine hydroxy analog (MHA) as supplements in soybean meal-based diets for sunshine bass, the hybrid of white bass Morone chrysops female x striped bass M. saxatilis male. Five practical diets were formulated to contain crude protein at 40% of dry weight, with 75% of the protein provided by soybean meal and 25% provided by menhaden fish meal. The basal diet provided total sulfur amino acids from intact protein at approximately 1.0% of dry diet, and the test diets were supplemented with each of the methionine compounds at 0.3% dry weight on an equal-sulfur basis (except for an additional 25% for MHA). A control diet was formulated to contain 40% crude protein exclusively from menhaden fish meal. All experimental diets were compared with a commercial diet containing 45% crude protein. Triplicate groups of juvenile sunshine bass (initial weights, 8-9 g/fish) were fed each diet in a brackish-water (5%) recirculating system for 8 weeks. Fish fed the soybean-meal-based diets supplemented with L-methionine, Dr-methionine, and acetylmethionine had weight gains and feed efficiencies similar to fish fed the commercial and control diets. However, MHA was not efficiently utilized by sunshine bass, and performance of fish fed that diet was significantly (P < 0.05) reduced, as was that of fish fed the basal diet. The highest protein efficiency ratio values were observed for fish fed the control diet and the diets supplemented with L-methionine and DL-methionine. Whole-body protein and moisture were not affected by the dietary treatments; however, differences in whole-body lipid and ash were observed among some treatments.