| Summary: | Five separate feeding trials were conducted to investigate branched-chain amino acid (BCAA) nutrition of red drum (Sciaenops ocellatus). First, the minimum dietary requirements of the BCAAs (leucine [Leu], isoleucine [Ile] and valine [Val]) were determined for juvenile red drum. Three independent 49-d feeding trials were conducted. Experimental diets were prepared by supplementing a basal diet containing 37 g/kg crude protein (CP) from red drum muscle (RDM) and crystalline amino acids (AAs) with incremental levels of Leu (9.0, 13.0, 17.0, 21.0, 25.0 and 29.0 g/kg of dry diet), Ile (5.0, 8.0, 11.0, 14.0, 17.0 and 20.0 g/kg of dry diet) and Val (6.8, 8.0, 9.2, 10.4, 11.6, 12.8 and 14.0 g/kg of dry diet). Fish in triplicate 30-L glass aquaria were fed each experimental diet to apparent satiation twice daily, after which growth performance parameters were measured. Incremental levels of dietary Leu, Ile and Val significantly affected weight gain, feed efficiency and protein retention. Analyses of the weight gain data using a broken-line regression model estimated the minimum Leu, Ile and Val requirements for maximum weight gain of juvenile red drum to be 15.7 ± 1.7 g/kg (± 95% confidence interval), 11.1 ± 2.3 g/kg and 12.4 ± 0.6 g/kg of dry diet, respectively. Secondly, the effects of high dietary levels of BCAAs on growth performance and AA utilization of juvenile red drum were determined. A semi-purified control diet (430 g/kg CP) was prepared by combining lyophilized RDM and crystalline AAs, while keeping the levels of Leu, Ile and Val at the minimum dietary requirement for red drum. Six experimental diets were prepared by supplementing the control diet with (1) an excess of Leu (62.0 g/kg of dry diet), (2) an excess of Ile (44.0 g/kg of dry diet), (3) an excess of Val (50.0 g/kg of dry diet), (4) an excess of Leu and Ile (62.0 and 44.0 g/kg), (5) an excess of Ile and Val (44.0 and 50.0 g/kg), and (6) an excess of Leu and Val (62.0 and 50.0 g/kg). Excess levels of Leu, Ile and Val corresponded to 200% of the ...
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