Refined understanding of sulfur amino acid nutrition in hybrid striped bass, Morone chrysops (male symbol) x M. saxatilis (female symbol)

Abstract

Previous studies have indicated the level of total sulfur amino acids (TSAA) (methionine + cystine) is most limiting in practical diet formulations for hybrid striped bass (HSB), especially if animal feedstuffs are replaced with plant feedstuffs. Reduction of costly animal feedstuffs such as fish meal while maintaining adequate dietary levels of TSAA may enhance cost effectiveness of production. Therefore, this study, consisting of four separate feeding trials, investigated three different aspects of sulfur amino acid nutrition of HSB including: (1) the efficacy of crystalline methionine hydroxy analog (MHA) and liquid MHA (AlimetTM) relative to L-methionine in meeting the requirement for TSAA; (2) the cystine sparing value for methionine; and, (3) the influence of various sulfur amino acid supplements on ammonia excretion. During the feeding trials, juvenile HSB were fed various diets including a basal diet deficient in TSAA (0.33 or 0.51% of diet), and experimental diets supplemented on an equalsulfur basis with different levels of either L-methionine, AlimetTM or crystalline MHA. Diets containing TSAA at 1% of diet and different ratios of cystine to methionine (60:40, 55:45, 50:50, and 45:55) also were fed to re-evaluate sparing effects of cystine on methionine. During the ammonia excretion trial, HSB were fed diets containing either L-methionine,AlimetTM or crystalline MHA after which total ammonia nitrogen (TAN) excretion was determined 4 h postprandial. In trial 1, AlimetTM was 73% as effective in promoting growth as L-methionine at the same concentration while MHA was 83% as effective. In trial 3, fish fed AlimetTM at 1.25% of diet displayed similar growth performance as those fed TSAA at 1.0% of diet while weight gain of fish fed AlimetTM at 1% was only 58% of that displayed by fish fed TSAA at 1.0%. No significant differences in weight gain, feed utilization or survival were observed among fish fed diets containing various ratios of cystine to methionine although the diet with 60:40 cystine to methionine supported the lowest responses. Inclusion of MHA or AlimetTM did not affect TAN excretion of HSB. These findings will aid in refining diet formulations for HSB to ensure adequate sulfur amino acid nutrition.