Qualidade de água e desempenho zootécnico de juvenis de tilápia do Nilo (Oreochromis niloticus) cultivados em sistema de bioflocos, com restrição de dieta comercial, suplementado com metionina sintética e óleo de soja

Abstract

The present study evaluated water quality and zootechnical performance of Nile tilapia juveniles grown in a biofloc system with commercial diet restriction, supplemented with synthetic methionine and soy oil. For this, three consecutive experiments were carried out. In the first experiment, the experimental design consisted of two control groups (1 - without dietary restriction, without supplementation with methionine; 2 - with dietary restriction of 25%, without supplementation with methionine) and four experimental treatments with dietary restriction of 25% and supplementation 0.5; 1.0 and 2.0% of DL-methionine to the ration, respectively, and supplementation of molasses in 1.0% of DL-methionine. Weight gain of fish reared in tanks with feeding restriction and dietary DL-methionine supplementation at 1% or 2% has not differed (p>0.05) from the tanks without feeding restriction. It has been concluded that it is possible to restrict the daily feeding allowances of tilapia juveniles reared in BFT tanks at 25%, with no growth performance impairment, if a minimal dietary DL-methionine supplementation of 1.0% is carried out. In the second experiment, the control groups performed in the first experiment were repeated. In the other treatments, juvenile tilapia, raised in BFT tanks, were restricted in feed supply by 25% and 0.6%, 1.2% and 2.4% soy oil were added daily to the feed, respectively. In addition to these treatments, there was one in which 1.2% soy oil was added to the molasses. FBW, SGR, weekly weight gain and fish productivity were hindered by reduced feed supply. The incorporation of soybean oil in the diet did not improve the zootechnical performance of tilapia. It has been concluded that the supplementation of the tilapia juveniles’ commercial diet with increasing levels of soybean oil, reared in BFT tanks submitted to artificial diet feeding restriction, was no capable to prevent the deterioration of the animal’s growth performance. In the last experiment the fish were grown in BFT tanks, with or without the use of restrictive rates of 25% in the supply of commercial feed, and with levels of inclusion of DL-methionine (0% and 1.0%) and / or soy oil (0%, 0.6% and 1.2%) in the feed. The water quality was affected only by the amount of feed offered. The 25% reduction in feed supply without DL-methionine and soy oil supplementation impaired FBW, WWG and fish yield in relation to unrestricted tanks. The combined use of DL-methionine and soybean oil in artificial diets improves the survival of tilapia under feed restriction. It is concluded that the supplementation of DL-methionine in 1.0% and / or soy oil in 0.6% in artificial diets, with a 25% restriction, avoids worsening of the growth indexes.