Effects of black mustard (Brassica nigra) seed oil on growth performance, digestive enzyme activities and immune responses in rainbow trout (Oncorhynchus mykiss)

Abstract

In the present study, effects of black mustard seed oil administration on growth performance, digestive enzyme activities and immune response in rainbow trout (Oncorhynchus mykiss) were evaluated. Rainbow trout were fed with three different doses of black mustard seed oil at the rate of 0.5% (BM0.5), 1% (BM1) and 2% (BM2) along with a control with no supplementation (0%) for 60 days. On 30th and 60th day of the study, digestive enzyme activities and immune responses were examined. At the end of the feeding trial, growth performance and survival against Aeromonas hydrophila infection were also recorded. Growth was positively affected in BM2 fish group, but it was not significantly different. Amylase and lipase levels were not altered compared with control at any sampling time. However, trypsin was increased in all experiential fish groups compared with control (p < 0.05). Pepsin level increased in BM2 fish group only on 60th day of the study (p < 0.05). Respiratory burst activity was significantly decreased in BM2 fish group at both the sampling times compared with control (p < 0.05). Potential killing activity was elevated in BM2 fish group on 30th day (p < 0.05). Lysozyme activity was enhanced in BM1 and BM2 fish groups on 30th day and BM0.5 and BM1 groups on 60th day compared with that of the control (p < 0.05). MPO increased significantly in BM1 and BM2 fish group on 30th day and in all experimental fish groups on 60th day of the study compared with that of the control. No changes in histology of different organs of fish groups were observed. The pro-inflammatory cytokine, IL-1β gene expression in intestine of all treated fish groups was significantly upregulated on 30th day. Similarly, transcription of IL-8 and IL-6, IL-10 and IL-12 cytokine genes was enhanced in intestine cells on 30th day. Similar enhanced levels of these genes were observed in head kidney cells of BM0.5 and BM1 fish groups. Survival against A. hydrophila infection increased insignificantly in all BM-treated groups. All these results indicated that supplementation of BM could elevate intestinal immunity in rainbow trout, and the dietary incorporation of BM at 1%–2% level for 30 days is encouraged.