Lysine and sulfur amino acid requirements of juvenile blue tilapia (Oreochromis aureus)

Abstract

Growth studies were conducted with fingerling blue tilapia (Oreochromis aureus) to determine lysine and methionine requirements, and the cysteine replacement value for methionine. The fish were fed experimental diets formulated from purified ingredients to contain 30% crude protein and 3.1 Kcal/g diet. Casein and gelatin served as intact protein sources and were supplemented with crystalline L-amino acids to provide the amino acid pattern found in 30% crude protein formulated from casein and gelatin. In the absence of cysteine, the lysine and methionine requirements (weight-gain basis) for blue tilapia were 1.29 (plus or minus sign) 0.11% and 0.83 (plus or minus sign) 0.04% of the dry diet, respectively, which corresponds to 4.3% and 2.8% of the dietary protein. The cysteine replacement value for methionine on an equal sulfur molar basis was found to be about 44 (plus or minus sign) 1.6%. Serum free lysine and methionine did not reflect the requirements determined from growth studies. There did not appear to be a lysine-arginine antagonism over the dietary lysine range used in the lysine requirement study. Amino acid composition of eggs, muscle and whole-body tissue of three different sizes of blue tilapia were also determined..