Castillo Alvarado, Sergio A (2017-12). The Role of Branched-Chain Amino Acids in the Aquaculture of Red Drum, Sciaenops ocellatus L. Defining Dietary Requirements and Elucidating Antagonistic Effects. Doctoral Dissertation.
Thesis
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 amount found in a diet with 350 g/kg CP provided by RDM. Red drum juveniles were stocked in 38-L glass aquaria (12 fish/aquarium), and diets were fed to fish in triplicate aquaria at a rate approaching apparent satiation, twice daily, for 49 d. At the end of the feeding trial, growth performance parameters were calculated and the postprandial concentration of BCAAs in plasma was analyzed. Growth performance of the red drum was significantly affected by an excess of dietary Leu, alone or in combination (Leu+Ile and Leu+Val), confirming an antagonistic effect due to the imbalanced concentration of BCAAs in the diet. In addition, the postprandial concentration of plasma Leu, Ile and/or Val was significantly higher in fish fed an excess of Leu, Ile and/or Val, respectively. Nonetheless, postprandial levels of BCAAs in plasma did not indicate that an excess of Leu blocked the intestinal absorption or promoted the catabolism of Ile and/or Val in red drum, as has been reported in other species. Ultimately, the results obtained from this dissertation will facilitate the production of aquaculture feeds composed of alternative protein ingredients while maintaining an ideal AA profile for optimal performance of red drum.
