Effects of black mustard seeds (Brassica nigra) and nettle seed (Urtica dioica) oils on growth performance, digestive enzyme activity and immune responses of rainbow trout (Oncorhynchus mykiss)

In this study, the effects of black mustard (Brassica nigra) and nettle seed (Urtica dioica) oils on growth performance, digestive enzyme activities and immune responses in rainbow trout (Oncorhynchus mykiss) were investigated. Also, at the end of the study, the fish were injected intraperitoneally with Aeromonas hydrophila and the survival rates of the fish were recorded for 14 days. For this purpose, fish were fed diet containing different doses of black mustard and nettle seed oil at the rate of 0% (Control), 0.5% (SH,5); 1% (SH1); 2% (SH2) for black mustard and 0% (Control), 0.5% (IY0.5) 1% (IY1) and 2% (IY2) for nettle seed during 60 days. On the 30th and 60th days of the study, blood and tissue (kidney, intestine and stomach) samples were taken from the fish and the changes in digestive enzymes and immune responses were examined. Amylase was increased 30th day of the study in IY groups compared to control. No differences were observed at the end of the study. Trypsin was elevated in all sampling time in all experimental groups compered to control (P<0.05) except in IY1 groups on 30th day (P>0.05). Pepsin was increased in IY groups on 30th day of the study compared to control (P<0.05). This increase was observed only in SH2 group at the end of the study (P<0.05). Lipase was up regulated on IY0.5 group and down regulated in SH0.5 group compared to control (P<0.05) on 30th day of the study. Respiratory burst was significantly decrease on SH2, IY0.5 and IY2 on 30th day of the study. At the end of the study respiratory burst was similar with SH0.5 and IY1 (P>0.05) and all the other groups were significantly decreased (P<0.05). Increased potential killing activity as determined on 30th day of the study in SH2 and IY32 groups compared to control (P<0.05). Lysozyme activity was significantly increased in SH1 and SH2 groups compared to control. At the end of the study, this increase was observed in SH0.5, SH1and IY2 groups compared to control (P<0.05). Myeloperoxidase was significantly increased in SH1 and SH2 groups compared to control. No differences were observed in IY groups compared to control (P>0.05). at the end of the study, all groups myeloperoxidase activity was significantly increased compared to control (P<0.05). IL-1β gene expression levels in the anterior kidney was observed in the IY0.5 group and IY2 on the 30th day of the study. Almost all groups IL-1β was upregulated in the intestine on 30th day of the study. IL-6 was only up regulated at the end of the study in IY0.5 group in the kidney. In the intestine all groups Il-6 gene expression was significantly increased compared to control. IL-8 was not showed any differences on 30th day of the study in all experimental groups compared to control in the kidney. However increased activity was determined on 60th day of the study in all IY groups (P<0.05). In the intestine all groups IL-8 was significantly increased. No differences observed at the end of the study (P>0.05). IL-10 was significantly up regulated in the intestine in all experimental groups compared to control (P<0.05) on 30th day of the study. Also elevated IL-12 was determined in the intestine on 30th day of the study. At the end of the study, growth performance was not significantly affected among experimental groups. All groups survival rate was significantly increased compared to control after challenged with Aeromonas hydrophila. All these results show that black mustard and nettle seed oils can increase the digestive enzyme activities of rainbow trout and can be used as an immunostimulant.