Add time:07/28/2019         Source:sciencedirect.com

Imbalanced dietary levels of branched-chain amino acids (BCAAs) are known to produce antagonistic effects in pigs, rats and humans, affecting the concentration of BCAAs in plasma and ultimately depressing growth. In fish, antagonism involving BCAAs has not been fully characterized or understood. The objective of this study was to determine the effects of imbalanced dietary levels of BCAAs on growth performance and amino acid utilization of juvenile red drum. A control diet was prepared by combining lyophilized red drum muscle and crystalline amino acids, while keeping leucine (Leu), isoleucine (Ile) and valine (Val) at the previously quantified minimum dietary requirement levels for red drum. Six experimental diets were prepared by supplementing the control diet with (1) an excess of Leu, (2) an excess of Ile, (3) an excess of Val, (4) an excess of Leu and Ile, (5) an excess of Ile and Val, and (6) an excess of Leu and Val. Red drum juveniles were stocked in 38-L glass aquaria, and diets were fed to fish in triplicate aquaria, twice daily, for 45 d. At the end of the feeding trial, growth performance was evaluated and postprandial levels of BCAAs in plasma were analyzed. Growth performance of red drum was significantly depressed by an excess of dietary Leu, but not by an excess of Ile nor Val. The postprandial concentration of plasma Leu, Ile or Val was significantly higher in fish fed an excess of Leu, Ile or Val, respectively. 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. However, excess Leu did significantly reduce the postprandial concentration of α-ketoglutarate in plasma, possibly indicating a higher ratio of transamination due to the imbalanced postprandial concentration of BCAAs in plasma. In conclusion, an antagonistic effect due to excess dietary Leu was confirmed in juvenile red drum. This study represents a step forward in understanding the nature of the antagonistic effects among BCAAs in fish.

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