Effect of environmental thermal fluctuations on innate immune responses in pacu Piaractus mesopotamicus juveniles

Immune functions in teleosts are straightly influenced by environmental temperature. Low temperatures usually affect negatively the immune status of fishes favoring the incidence of diseases. Immune cells in fishes are protected from peroxidation by dietary vitamin E. Innate immune defenses of Piaractus mesopotamicus were evaluated in fish fed with diets supplemented with vitamin E for 45 days. The fish endured decreases in environmental fluctuations of temperature for 24 and 72 h. The most effects were observed at the 24th hour, in which the level of plasma cortisol increased independently of dietary supplement of vitamin E and a lessening of MNL and a raise of GL counting were observed in fish fed with supplemented diets. The lowest SL variation was observed in fish fed with the maximum level of vitamin E, but the dietary vitamin E decreased the HAC. However, the stressing condition increased HAC. Dietary vitamin E used in the present experimental conditions did not present remarkable effects on the immune frame of pacu to cope with environmental thermal fluctuations but other investigations concerning the vitamin half-life and its association with unsaturated dietary lipids seem to be fundamental.