Abstract
The present study investigated the effects of dietary prebiotic galactooligosaccharide [(GOS), 1%], probiotic (Pediococcus acidilactici) [7.57 log CFU g-1] and synbiotic (GOS + P. acidilactici) on antioxidant enzymes activity and disease resistance of rainbow trout (15.04±0.52 g). After 8 weeks feeding on the experimental diets, liver catalase (CAT ), glutathione S-transferases (GST), glutathione reductase (GR) activities, and malondialdehyde (MDA) levels were measured. Thereafter, all fish were challenged by Streptococcus iniae. Probiotic, prebiotic and synbiotic had no significant effect on liver MDA level compared to the control group (P>0.05). However, CAT , GST and GR activities were significantly higher in the fish fed probiotic, prebiotic and synbiotic, compared to the control group (P<0.05). The highest CAT and GST activities were observed in the fish fed diet supplemented with synbiotic. There were no significant differences in GR activity among different groups (P>0.05). Bacterial challenge showed that feeding on probiotic, prebiotic and synbiotic remarkably increased resistance against S. iniae (P<0.05), with the highest resistance observed in the synbiotic group. The results indicated that although both GOS and P. acidilactici significantly increased antioxidant defence and improved disease resistance, combination of GOS and P. acidilactici had an additive effect. Combination of GOS and P. acidilactici is recommended to increase trout antioxidant capacity and streptococcosis.