Research Article: Study on the effects of red pepper (Capsicum annuum) extract on immune responses and resistance of rainbow trout (Oncorhynchus mykiss) juveniles against Yersinia ruckeri

The aim of this study was to investigate the effect of red pepper (Capsicum annuum) extract on growth, blood, biochemical and non-specific immune parameters of 360 rainbow trout (Oncorhynchus mykiss) juveniles with average weight of 9.38±0.01 g. The fish were fed with a commercial diet containing 0, 0.25, 0.5 and 1% of C. annuum extract in 12 tanks (300L) with three replicates (30 fish per tank) for 30 days. Then, Yersinia ruckeri was injected by intraperitoneal to evaluate fish resistance. At the end of fish feeding period, growth and survival, as well as blood and immune parameters were assessed. The highest level of weight gain (%) and SGR and also the least level of FCR were observed in fishes fed by 0.5% red pepper extract (p<0.05). Hematological parameters (RBC, WBC and hemoglobin) significantly increased in fish fed with 0.25 and 0.5% of C. annuum extract for 30 days and after challenging with Y. ruckeri as compared to the control group. Lysozyme and complement contents indicated significant increases in all treatments fed with red pepper extract after bacterial infection (p<0.05). Generally, it can be concluded that rainbow trout fed with 0.5 % red pepper extract for a month could gain more weight and enhance immune responses against infectious diseases.