Khodadadi, A.1, Haghighi, A2*, Malekinejad, H.3, 4, Tukmechi, A.5, Afsharnasab, M.6

Currently, global use of prebiotic compounds has increased considerably. This study aims to analyse the effect of complementing the rations of rainbow trout with different concentrations of Celmanax® prebiotic, which contains Saccharomyces cerevisia associated compounds with Mannan-oligosaccharide on gill and liver histology during the growing period and experimental challenge with yersiniosis. Four concentration levels of prebiotic (0, 0.1, 0.5 and 1%) were mixed into fish feed pellets. The fish (with mean body weight of 19.08±1.45 gr) were fed a supplemented commercial diet for 60-days.On day 60 of the study, experimental yersiniosis was induced in all treatment groups by intraperitoneal injection of bacterial suspension. Tissue samples were taken on days 0, 30 and 60 and also after induction of experimental yersiniosis. The results showed that complementing rainbow trout rations with different concentrations of Celmanax® improved the gill and liver injuries on days 30 and 60 of the study. The best tissue effects in the growing period were observed in treatment groups which received 0.1% and 0.5% of the prebiotic respectively, and after experimental challenge with yersiniosis, the lowest lesions of liver and gill pathology were seen in the treatment group fed with 0.1% prebiotic which was significantly different (p<0.05) from all other treatments. According to the results of this study, adding Celmanax® to rainbow trout diet at 0.1% concentration improves tissue parameters during breeding period and decreases tissue lesions when faced with yersiniosis.