Effect of dietary supplementation of red chili pepper (Capsicum annuum) powder on growth parameters, survival rate, hematological indices and some immunity responses of rainbow trout (Oncorhynchus mykiss) fry

To investigate the effect of red spicy pepper on growth, blood parameters and immune responses of rainbow trout, 240 fingerlings (mean weight 15.69±0.33 g) were randomly distributed into 12 tanks (20 individuals per tank) and they were fed with 0, 1, 3, and 5% red chili pepper (Capsicum annuum) powder in their diet (each with three replicates) for 45 days. The results of growth indices showed that the highest level of body weight gain and specific growth rate were observed in 5% treatment compared to the other treatments (P<0.05). The lowest value of the feed conversion ratio was observed in treatments fed 3% and 5% red pepper. In addition, no significant differences were observed in the condition factor among the treatments (P<0.05). The highest survival rate was observed in 3% and 5% pepper treatments and this index was not significantly different between the treatment 1 and control (P<0.05). The highest number of red blood cells was observed in 3 and 5% treatments (P<0.05). The highest percentage of hematocrit was observed in 5% pepper treatment (P<0.05). The highest white blood cell was related to the fish fed with red pepper-supplemented diets compared to the control group. The highest percentage of lymphocytes was observed in 5% pepper treatment. The highest levels of lysozyme activity, C3, and IgM were observed in 5% pepper treatment, which was significantly different from other treatments (P<0.05). Also, C4 level significantly increased in the pepper-fed treatments (P<0.05). Overall, supplementing rainbow trout diet with 5% spicy red pepper powder improved growth performance, nutrition efficiency and immune system of rainbow trout fry.