METABOLIC RESPONSES OF NILE TILAPIA Oreochromis niloticus TO METHIONINE AND TAURINE SUPPLEMENTATION

Most plant protein sources used in aquafeeds formulations has limiting levels of sulfur amino acids (methionine and cysteine) which may restrict the level of inclusion of these ingredients. Methionine (MET) is an essential amino acid for fish and usually the first limiting amino acid in soy-based diets. Besides being used for protein synthesis, MET is a source of sulfur required for cysteine (CYS) and taurine (TAU) synthesis that occurs mainly in hepatic tissues. Additionally, plant proteins are low in TAU and this beta sulfonic amino acid has been shown to be an essential amino acid for many marine fish species and some freshwater species. Therefore, the objective of the present study was elucidate the effects of MET and/or TAU supplementation in diets for Nile tilapia (Oreochromis niloticus), evaluating growth performance and expression of genes involved in sulfur amino acid metabolism.

The experiment was conducted at the Texas A&M University Aquacultural Research and Teaching Facility during 8 weeks. Two-hundred and seventy Nile tilapia juveniles (initial weight 4.84 ± 0.04 g) were randomly distributed into 18, 110-L aquaria in an entirely randomized design containing six treatments with three replicates (n = 15 fish per aquarium). Six isonitrogenous (28.4% of crude protein) and isoenergetic (3875 kcal gross energy kg^-1) diets based on soybean products were supplemented with or without MET and TAU in a 2x2 factorial arrangement to evaluate deficient or adequate levels of these two amino acids singularly and in combination. In addition, a control diet formulated with fishmeal (positive control that provide adequate levels of MET and TAU) and another soybean-based diet supplemented with higher levels of MET and TAU (above that required by Nile tilapia) were included.

There is a significant effect of MET and TAU supplementation on Nile tilapia growth (Table 1). The current experiment demonstrates that TAU may spare methionine.  Analysis of gene expression and amino acid composition of the present study is currently been processed, and all results will be included in the final presentation.