Growth, physiological and immune responses of Arapaima gigas (Arapaimidae) to Aeromonas hydrophila challenge and handling stress following feeding with immunostimulant supplemented diets.

The current study tested the efficacy of a dietary immunostimulant additive (Aquate Fish™®) on the growth performance, and on the physiological and immune responses of Arapaima gigas. Two trials were carried out: a feeding trial for 30 days with the experimental diets and a challenge trial for 7 days, in which fish were bacterial challenge (Aeromonas hydrophila) following by 60 s handling stress. During the feeding trial, fingerlings were fed diets supplemented with 0 (control), 6, 9 and 12 g Aquate Fish™®/kg diet. Dietary supplementation did not influence feed intake, feed conversion and condition factor, but increased the final biomass, number of erythrocytes, thrombocytes, leukocytes, lymphocytes, monocytes, hemoglobin, glucose, globulins and plasma triglycerides in fish fed at a concentration of 12 g/kg diet. After bacterial infection, mortality occurred only in fish fed control treatment, whereas respiratory burst of leukocytes, number of leukocytes and lymphocytes increased in fish that received 12 g of dietary supplementation. The results indicated that dietary supplementation with 12 g of Aquate Fish™® improved biomass and immunity performance of A. gigas fingerlings, without negatively affecting blood biochemical parameters.