Bovine colostrum is a rich source of immunological factors and contains a large concentration of antioxidant components that can affect gut physiology. Thus, the antioxidant potential was evaluated in the gut of juvenile pacu (Piaractus mesopotamicus, Holmberg, 1887), an omnivorous fish, and dourado (Salminus brasiliensis, Cuvier, 1816), a carnivorous fish, fed with diets containing 0, 10 and 20% of lyophilized bovine colostrum (LBC) for either 30 or 60 d. The antioxidant capacity in the intestinal tissue was assessed by the determination of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and by the oxygen radical absorbance capacity (ORAC value expressed as equivalent trolox in µM/mg of protein). Experimental design was completely randomized with treatments arranged as a 3 × 2 factorial, considering the 3 diets and the 2 periods as main effects. If F value was significant, Tukey test was used for comparisons between means (P < 0.05). In pacu, interaction between diet and period was observed to SOD (P < 0.05), juveniles fed 0 and 10% LBC did not change enzyme activity at 30 (423 ± 27 and 692 ± 42 U/mg of protein, respectively) and 60 d (504 ± 14 and 890 ± 57 U/mg of protein, respectively), whereas juvenile fed 20% LBC showed higher enzyme activity at 60 d (1122 ± 71 U/mg of protein) compared with 30 d (595 ± 61 U/mg of protein). GPx was not influenced by diet and period (P > 0.05) and CAT was affected only by period (P < 0.05), showing higher activity at 60 d (891 ± 86 U/mg of protein) compared with 30 d (437 ± 99 U/mg of protein). The ORAC was affected by diet and period (P < 0.05); the juveniles fed 10% LBC (505 ± 100 µM/mg) had greater oxygen absorbance capacity than the juveniles fed 20% LBC (348 ± 104 µM/mg), and the value was greater at 30 (628 ± 61 µM/mg) than at 60 d (234 ± 31 µM/mg). In dourado, GPx was affected by period (P < 0.05), showing greater activity at 30 (224 ± 30 U/mg of protein) than at 60 d (94 ± 19 U/mg of protein). SOD, CAT and ORAC value were not affected by diet and period (P > 0.05). Inclusion of lyophilized bovine colostrum improved SOD activity in the gut of juvenile pacu, an omnivorous fish, indicating a possible protective action of this lacteal secretion.