A balanced dietary amino acid profile improves amino acid retention in post-larval Senegalese sole (Solea senegalensis)

The rearing of most marine fish larvae still relies on live food. Dietary amino acid (AA) imbalances when using live food in the larval rearing of flatfishes have been suggested. The aim of this study was to test if dietary AA supplementation affects AA metabolism in Senegalese sole (Solea senegalensis) post-larvae. This was done by tube-feeding Artemia-fed sole with a dipeptide solution containing two potential limiting AA (leucine and phenylalanine), in order to supplement the larval gut content and to balance the dietary AA profile. Two experiments were done using different C-14-labelled AA as tracers. The first used a C-14-protein hydrolysate to test the effect of balancing the dietary AA profile on the overall AA metabolism. The second experiment analysed the effect of balancing the dietary AA profile on metabolism of three-selected AA: arginine, leucine and glutamate. A set-up to determine the handling of C-14-labelled AA was used, in order to quantify the absorption, catabolism and retention of the test mixtures by the sole post-larvae. The first experiment demonstrated that, when fish were fed the dipeptide supplement, AA catabolism decreased and AA retention increased. This agrees with the hypothesis that balancing the dietary AA profile increases AA retention in fish. In the second experiment, arginine and glutamate catabolism were reduced by the dipeptide supplementation. Leucine supplementation did not reduce leucine catabolism but instead increased arginine and glutamate retention. This result supports earlier studies that fish larvae are able to regulate their AA metabolism. A balanced dietary AA profile increases the AA retention and may improve growth and nitrogen utilisation. (C) 2004 Elsevier B.V All rights reserved.