Níveis nutricionais de lisina e metionina+cistina digestíveis para juvenis de tilápia-do-nilo (Oreochromis niloticus)

Abstract

Aiming to determine the nutritional needs of lysine and methionine+cystine for juvenile Nile tilapia (Oreochromis niloticus), Thai strain, two experiments were conducted at the Laboratory of Aquaculture Department of Animal Science, Federal University of Espirito Santo, with 30 days each. In the first experiment aimed to evaluate the nutritional need of lysine to this, we used 720 juvenile Nile tilapia with initial weight of 7.30 ± 0.11 g, distributed in a completely randomized design with eight treatments, six replications and fifteen fish per experimental unit. The tilapia were divided into 48 polyethylene tanks with a volume of 60L, with individual aeration and temperature controlled recirculation system with minimum water renewal of 50% per day. Treatments consisted of eight diets (26.81% of digestible protein and 3090 kcal/kg digestible energy) containing different levels of digestible lysine (1.24, 1.36, 1.48, 1.60, 1.72; 1.84, 1.96 and 2.08%). We evaluated the performance variables (weight gain, specific growth rate, survival rate, feed intake, digestible lysine intake, feed conversion, protein efficiency for gain, efficiency of lysine for gain and efficiency of retention nitrogen) and body composition (moisture, fat, protein, ash body and deposition rates of daily protein and fat). The high levels of dietary lysine did not affect (P>0.05) feed intake, the survival rate and the moisture and ash body, but improved quadratic (P<0.05) the other parameters, except for lysine intake and efficiency of lysine for gain, which increased and decreased, respectively, linearly (P<0.05). It is recommended that diets for juvenile Nile tilapia should contain 1.84% digestible lysine for maximum weight gain. In the second experiment aimed to evaluate the nutritional requirements of methionine+cystine, were used for both 1260 juvenile Nile tilapia with initial weight of 0.80 ± 0.03 g, distributed in a completely randomized design with seven treatments six replicates and thirty fish per experimental unit. The tilapia were divided into 42 polyethylene tanks with a volume of 300L, with individual aeration and temperature controlled recirculation system with minimum water renewal of 25% per day. Treatments consisted of seven diets (26.80% of digestible protein and 3090 kcal/kg digestible energy) containing different levels of methionine+cystine (0.68, 0.80, 0.92, 1.04, 1, 16, 1.28 and 1.40%). We evaluated the performance variables (weight gain, specific growth rate, survival rate, feed intake, digestible lysine intake, feed conversion, protein efficiency for gain,