Effects of fenugreek (Trigonella foenum graecumL.), black mustard (Brassica nigra) seeds and laurel (Laurus nobilis) leaves extract on immune response and growth performance in rainbow trout (Oncorhynchus mykiss)

In this study, the effects of aqueous methanolic extracts of seeds of fenugreek (Trigonella foenum-graecum L.) and black mustard (Brassica nigra), and leaves of laurel (Laurus nobilis) on growth performance, some immune parameters, IL-1β, IFN-1, TGF-β ve TNF-α gene expressions levels, and survival rate after challenging with Vibrio anguillarum, Yersinia ruckeri and Aeromonas salmonicida pathogens were investigated in rainbow trout (Oncorhynchus mykiss). In the study, 25 fish were reared in each tank and each dose consisted of three replicates. During the study, the fish were fed 3 times a day ad libitum with feeds that contain 3 different doses for each plant extract (0.1 g/kg; 1 g/kg; 5 g/kg) which were added into the feed by spraying and control feed (0 g/kg) for 45 days. Sampling was carried out every 15 days and during the sampling, first, the fish along with the feed were weighed, and feed conversion ratio (FCR), specific growth rate (SGR), and weight gains (WG) were determined. Subsequently, humoral immune responses such as superoxide radical releases (NBT), lysozyme (LYS), and myeloperoxidase (MPO) activities and cytokine gene expressions were investigated by taking blood and tissue samples. At the end of the study, the fish were injected intraperitoneally with Vibrio anguillarum, Yersinia ruckeri, and Aeromonas salmonicida, and the survival rates (SR) of the fish for 10 days were determined. As a result, there was no significant difference in growth performance parameters in all extract-containing groups compared to the control group (P>0.05). Considering the NBT results, the highest increase was observed in the D5 group on the 15th day, but a statistically significant difference was found only with the Ç0.1 group (P<0.05). On the other hand, it was determined that the highest increase was in the SH5 group on the 30th day (P<0.05) however, there was no difference in any group compared to the control on the 45th day (P>0.05). There was no significant difference between groups in terms of lysozyme activity in all sampling times (P>0.05). Regarding the myeloperoxidase activity, on the 15th day, while the SH1 group showed similarity only with SH5 and D5 groups, it showed a significant increase compared to other groups (P<0.05), and there was no difference between groups in other sampling times (P>0.05). When the gene expression levels of IL-1β, IFN-1, TGF-β, and TNF-α were examined, it was observed that there were remarkable increases in kidney and spleen in different groups compared to the control group in different sampling times, while the gene expression levels were also determined to be significantly lower in different groups compared to the control group in different sampling times (P<0.05). The challenge test SH0.1 group showed the highest survival rate against the Aeromonas salmonicida pathogen, whereas the SH1 and SH5 groups exhibited similar results with the SH0.1 (P>0.05). The lowest survival rate, on the other hand, was found to be in the D0.1 group which was significantly different from other groups (P<0.05). In the challenge test performed with Vibrio anguillarum, Ç1 and SH5 groups showed the highest survival rate by exhibiting significantly different results from other groups (P<0.05). Again, the D0.1 group showed the lowest survival rate with a significant difference. Against the Yersinia ruckeri pathogen, the highest survival rate was found in the Ç5 group with a significant difference (P<0.05). The lowest survival rates were observed in the SH1 and SH5 groups, and the results of these groups were similar to the result obtained from the control group (P>0.05). All these results suggest that the addition of aqueous methanolic extract of laurel (Laurus nobilis) leaf into the feed at the rate of 0.1 g/kg is not effective as an immunostimulant. However, it was determined that some plant extracts used at different rates can be used as immunostimulants. It can be concluded that the addition of aqueous methanolic extract of fenugreek seeds to the feed at the rates of 1 and 5 g/kg increases the immunity, based on the high gene expression levels and low mortality rates determined in this study.