Effect of lysine and tyrosine supplementation in the amino acid metabolism of Diplodus sargus larvae fed rotifers

Dietary amino acid imbalances are likely to happen when fish larvae are fed live food. This can lead to reduced growth as well as decreased larval quality. The tube-feeding technique can be used to assess the effect of free amino acid supplementation at short term and determine whether a given amino acid is deficient in the diet. In this study supplementation of lysine and tyrosine were tested in Diplodus sargus larvae fed rotifers in order to determine its effect on the metabolism of these amino acids. Supplementation was done using rotifers enriched with liposomes boosted with free amino acids. Single crystalline 14C amino acids as well as a mixture of 14C amino acids were used as tracers to compare results of individual amino acid metabolism with the average of all amino acids. The results showed low absorption efficiencies for both tyrosine and lysine when compared to the average of all amino acids. A lower relative 14C retention was found when D. sargus larvae were fed tyrosine enriched rotifers and tube-fed 14C tyrosine, indicating that tyrosine was not a limiting amino acid. On the other hand, lysine supplementation had a similar retention percentage in the treatments with and without lysine supplementation. Based on the tube-feeding studies with lysine and tyrosine supplementated rotifers neither lysine nor tyrosine affected protein synthesis in a way to indicate that these amino acids are insufficient in D. sargus larvae fed rotifers.