Avaliação de respostas metabólicas e de imunidade inata em pacu (Piaractus mesopotamicus, Holmberg, 1887) alimentados com dietas suplementadas com vitamina E e submetidos à variação de temperatura

Abstract

Demands for seafood are growing in the whole world and the fish farming industries are in frank development over the last decade. However, stressful conditions, which favor higher incidence of diseases and impair growth in fishes, are usually found in fish farming. Therefore, several studies are focused in the improvement of management to reduce stress and keep the animals healthy, reducing losses in farm production. The use of immunostimulants in the diets, such as vitamin E, has been suggested as an alternative to improve fish resistance to diseases under stressful conditions. Pacu, Piaractus mesopotamicus, is one of the main species from the Brazilian aquatic fauna and is of great importance in fish farming. Hence, the objective of this study was to evaluate the metabolic responses and innate immunity of pacu fed with vitamin E supplemented diets and challenged to temperature variation. The experiment was conducted as a totally randomized design in a factorial scheme 3x3x2, with three levels of dietary vitamin E (0, 100 and 300 mg/kg), three sampling spans (0, 24 and 72h) and two temperature conditions (controlled and variable), with four replicates (tanks) per treatment. The main responses observed to cope with stress were 1) elevation of plasma cortisol in the animals subjected to temperature variation, independent of the concentration of vitamin E in the diet, 2) hyperglycemia only in the animals subjected to temperature variations and fed with not supplemented diets and 3) hyperlactemia in the fish subjected to temperature variation and fed with not supplemented and supplemented diets with 300 mg of vitamin E. Animals fed with diets supplemented with 100 mg of vitamin E and subjected to temperature variation depicted the highest percentage of granular leukocytes, the highest concentration of serum lysozyme and the highest activity of alternative complement pathway. There upon, supplementation with 100 mg of vitamin E seems to be the best one for this species under the studied conditions.