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Evaluation of Dietary Supplementation of Graded Levels of β-Hydroxy-β-Methylbutyrate for Hybrid Striped Bass Morone chrysops × M. saxatilis

ABSTRACT Leucine is traditionally regarded solely as an indispensable amino acid which is abundant in most protein feedstuffs used in fish diets. However, the beneficial influences of a leucine metabolite, β-hydroxy-β-methyl-butyrate (HMB), on growth and/or immune responses have been reported for various animals including fishes. Therefore, the present experiment was conducted to evaluate HMB with hybrid striped bass Morone chrysops × M. saxatilis. A basal diet containing 40% crude protein from menhaden fish meal was supplemented with four incremental levels of HMB (50,100, 250, and 1,000 mg/kg diet) at the expense of cellulose. Three groups of juvenile hybrid striped bass (10.2 ± 0.3 g/fish, 16 fish/group) were fed each experimental diet for six weeks, followed by an immersion challenge with Streptococcus iniae. Whole-body composition and innate immune responses also were analyzed at the end of the six-week feeding period. Dietary supplementation of HMB failed to improve weight gain and feed efficiency of juvenile hybrid striped bass as well as intracellular and extracelluar superoxide anion production of head kidney cells and serum lysozyme activity. Only marginal effects of HMB on blood neutrophil oxidative radical production and resistance of hybrid striped bass to S. iniae infection were observed. However, dietary supplementation of HMB significantly (P < 0.01) increased the whole-body lipid content of juvenile hybrid striped bass.