Previous studies have indicated that the level of total sulphur amino acids (TSAA) (methionine1cystine) is most limiting inpractical diet formulations forhybrid striped bass (HSB), especially if animal feedstu¡s are replacedwithplant feedstu¡s.Reduction incostlyan- imal feedstu¡s such as ¢sh meal, while maintaining adequate dietary levels of TSAA, may enhance the cost e¡ectiveness of production.Therefore, this study investigated three di¡erent aspects of sulphur amino acid nutrition of HSB including: (1) the e⁄cacy of crystalline methionine hydroxy analogue (MHA) and liquid MHA (AlimetTM)relative to L-methionine in meeting the requirement for TSAA; (2) the cy- stine-sparing value for methionine; and (3) the in£u- ence of various sulphur amino acid supplements on ammonia excretion. During three separate feeding trials (2, 6 and 10 weeks in duration), juvenile HSB were fed various diets including a basal diet de¢cient in TSAA (0.33% or 0.51% of diet), and experimental diets supplemen- ted on an equal-sulphur basis with di¡erent levels of either L-methionine, AlimetTM or crystalline MHA. Diets containing TSAAat1% of diet and di¡erent ra- tios of cystine to methionine (60:40,55:45,50:50 and 45:55) were also fed to re-evaluate the sparing e¡ects of cystine on methionine. In trial 1, over the course of 10 weeks, AlimetTM was 73% as e¡ective in promoting weight gain as L-methionine at the same concentrationwhile MHA was 83%as e¡ective. After 6 weeks in trial 2, ¢sh fed AlimetTM at 1.25% of diet displayed similar growth performance as those fed TSAAat1.0% of diet, while weight gain of ¢sh fed AlimetTM at1% was only 58% of that displayed by ¢sh fed TSAAat1.0%. No signi¢- cant di¡erences in weight gain, feed utilization or survival were observed among ¢sh fed diets contain- ing various ratios of cystine to methionine, although the diet with 60:40 cystine to methionine had the lowest numerical responses. InclusionofMHAorAli- metTM did not a¡ect TAN excretion of HSB. These ¢ndings will aid in re¢ning diet formulations for HSB to ensure adequate sulphur amino acid nutrition.
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