A novel herbal immunostimulant for rainbow trout (Oncorhynchus mykiss) against Yersinia ruckeri.

In this 21-day study, we examined the effects of the aqueous methanolic extract of thin-skinned plum (Prunus domestica) on growth, immune response and resistance to a pathogenic bacterium, Yersinia ruckeri in rainbow trout (Oncorhynchus mykiss). Fish were fed with diets containing thin-skinned plum extract doses as 0 (Control) 0.1 (PD01), 0.5 (PD05) and 1% (PD1) ad libitum twice in a day. At the end of the study, growth was affected positively but not significantly. Feed conversion ratio (FCR) was decreased in the PD01 group (P < 0.05). There were elevated respiratory burst and potential bacterial killing activities on the 7th day in the PD1 fish group. No differences were observed in lysozyme activity (P > 0.05). An increased myeloperoxidase activity was recorded on the 14th day of study. Expression of interleukin and COX-2 genes was elevated on the 7th day of study in the kidney and intestine of treated fish. Histological results indicated no marked changes in organs (gill, kidney, liver and spleen) of PD treated fish groups. Challenge results of fish in all plum extract-treated groups showed an increased survival rate against Y. ruckeri (P < 0.05). This study indicated that the thin-skinned plum aqueous methanolic extract could improve innate immunity, survival against Y. ruckeri and decrease the FCR level.

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