Abstract
This study evaluated the effect of isonitrogenous and isocaloric diets based on animal protein (AP) and plant protein (PP), on growth performance, feed cost and body composition of tambaqui in the phases of on-growing and grow-out. Additionally, indicators of well-being, intermediate metabolism, digestive enzyme activity, innate immunity and endoparasitic load of fish were evaluated. In the on-growing, 90 tambaqui (13.98 ± 0.22 g) were randomly distributed in six experimental units with partial water renewal (400 L; n = 3; 15 fish/tank) and fed three times a day with the two experimental diets, for 60 days. For the grow-out phase, 24 tambaqui (86.02 ± 1.30 g) were kept in six experimental units (0.8 m3 net tanks; n = 3; 04 fish/tank) in a static system and fed twice a day with either of the two experimental diets for 70 days. In both experiments, the fish were fed until apparent satiety. In the on-growing phase, fish fed with the PP diet gained 64% more weight (p = 0.027), with apparent feed conversion being 9% better (p = 0.002) and feed cost being 12% lower (p = 0.004) than those fed with the AP diet. There no differences in the whole-body composition nor the digestive enzyme activity of the fish; however, adverse effects of the AP diet on the innate immunity of animals were observed, which may be related to the morphophysiological characteristics of the species and the imbalance of amino acids in the diet in relation to the requirements of the species. There was an 18% reduction in respiratory activity (p = 0.015) and a 35% reduction in total leukocyte count (p = 0.035), which was influenced by the low lymphocyte value (p = 0.004). In the grow-out phase, except for the higher energy utilization in AP diet (p = 0.000), there was no difference in performance between the fish fed the different diets. However, because of the reduction in the number of cells and leukocyte activity caused by the diets, there was a 59% increase in the average intensity of endoparasitic infestation (p = 0.028) in the tambaqui fed with AP diets. The results indicate that the use of a diet based on protein from plants and free of fishmeal provides greater growth during the on-growing phase of tambaqui. In the grow-out phase, this diet contributes to the resistance to endoparasitic infestation in the animals.