Interactive effects of dietary valine and leucine on two sizes of Japanese flounder Paralichthys olivaceus

• We estimate the interactive effects of valine and leucine on Japanese flounder.
• We use not only the growth performances but also blood parameters and oxidative stress conditions to estimate the interaction.
• Our research confirms the interactive effects of the two branched-chain amino acids on Japanese flounder.

This study was carried out to investigate the interactive effects of dietary leucine and valine on the performances of two sizes Japanese flounder Paralichthys olivaceus. Two groups of fish with average initial weights of 0.43 ± 0.01 g and 41.2 ± 2.0 g (mean ± S.D.) were fed with diets containing two levels of leucine (1.6 and 5.0% of diet) with three levels of valine (1.2, 1.8 and 2.5% of diet, as a 2 × 3 experimental design) and the control diet for 56 days and 30 days, respectively. In trial 1, after the fish fed with test diets for 56 days, growth performance and nutrients utilization were evaluated. Interactive effects of leucine and valine were found on growth parameters (final body weight, body weight gain and special growth rate) of Japanese flounder. Not only antagonism was observed in high dietary Leu level groups but also the stimulative effect of increased dietary Val in low Leu level groups. Significant interaction was also found on feed conversion ratio of Japanese flounder fed with test diets, however, the fish whole body proximate compositions were not altered by the various diets. In trial 2, dietary Leu and Val dominated the plasma free Leu and free Val concentrations, but no antagonism was found. Interactions were also found on plasma LDH and GPT of test fish, and it was showed that for fish fed with high dietary Val level in low Leu (1.6% of diet) diet can protect the cells from oxidative stress.