Nutritional requirements of total and digestible methionine + cystine for reversed fingerlings of the Nile tilapia <em>Oreochromins niloticus</em> (L.) based on the ideal protein concept

Abstract

The nutritional requirements of total and digestible methionine for reversed fingerlings of the Nile tilapia (Perciformes, Cichlidae) were determined. During a 40-day period fingerlings, weighing 1.31 ± 0.06g each, were fed on diets with 0.89; 0.94; 0.99; 1,09; 1.19 and 1.29% of total methionine + cystine, corresponding to 0.83; 0.88; 0.93; 1.03; 1.13 and 1.23% of digestible methionine + cystine. Since diets were supplemented with increasing levels of DL-methionine, diets reached 50.61; 0.54; 56.7; 62.80; 68.90 e 75% of methionine + cystine/lysine ratio (ideal protein concept), based on digestible amino acids values. Increasing methionine + cystine levels linearly diminished survival rate. Diets with 1.10% and 1.00% levels of total and digestible sulfur amino acid respectively had the best performance results for Nile tilapia fingerlings. This corresponds to 60.11 and 60.98% of total and digestible methionine + cystine/total and digestible lysine respectively.