Desempenho e resposta hematológica de tilápias do Nilo alimentadas com dietas com níveis crescentes de triptofano

Abstract

Tryptophan is an essential amino acid required in small amounts compared to the amounts of methionine, lysine, threonine and arginine. However, it has important functions in the animal body. The aim of this study was to evaluate the effect of tryptophan in the diet of Nile tilapia juvenile and, through the productive performance, body composition, amino acids retention, biochemical and haematological profile and subsequently evaluate the effect of the heat stimulus on the hematological and biochemical parameters (experiment 2). In both experiments, fish were distributed in a completely randomized design with five treatments and four replications. For the first experiment, were used 240 tilapias with an average weight of 38.20 ± 0.09 g, distributed in glass fibers boxes with a capacity of 250 liters, each unit was consisted of 12 fish. Four diets were prepared with approximately 243 g kg-1 of digestible protein and 3142 kcal kg-1 of digestible energy with increasing levels of tryptophan (2.11, 2.65, 3.19, 3.74 and 4.21 g kg-1). For the second experiment, were used 600 Nile tilapia with average weight and length of 3.39 ± 0.02 g and 5.07 ± 0.01 cm, respectively, distributed in 20 glass fiber boxes with a capacity of 250 liters, being each unit consisted by30 fish. Four diets were prepared with approximately 271.3 g kg-1of digestible protein and 3181 kcal kg-1 of digestible energy with increasing levels of tryptophan (2.11, 2.65, 3.19, 3.74 and 4, 21 g kg-1). After 85 days, there were analyzed the productive performance, hematological and biochemical parameters. Upon completion of these tests, for the third stage, 10 fish from each treatment were transferred to the laboratory where they were kept at a temperature of 350C for seven days. After a week the same hematological and biochemical analyzes realized before the thermal challenge were performed. Hematological parameters were evaluated for erythrocyte count (Eri), hemoglobin (Hb), percentage of hematocrit (Ht), mean corpuscular volume (MCV), mean corpuscular hemoglobin (HM), total leukocyte count (Leu), total thrombocytes count (Trom), percentage of lymphocytes (Linf), neutrophils (Neut) and monocytes (Mono), total plasma protein (TPP), plasma glucose (Gluc) and cortisol (Cort). For experiment 1, the tryptophan level of 2.11 g kg-1, corresponding to tryptophan: lysine ratio of 0.15:1, meets the dietary requirements for the health and productive performance of Nile tilapia. However, the best uniformity was obtained for fish fed with diets containing 2.65 to 4.28 g kg-1 of tryptophan. In experiment 2, the tryptophan level of 2.33 g kg-1, corresponding to tryptophan: lysine ratio of 0.157:1 was enough to meet the dietary requirements of the species healthiness. The heat stimulus did not changed the state of fish health.