Effects of Holy Basil (Ocimum sanctum) Extract on the Growth, Immune Response and Disease Resistance against Streptococcus agalactiae of Nile Tilapia (Oreochromis niloticus)

This study was conducted to investigate the effects of supplementing the diet of Nile tilapia (Oreochromis niloticus) with holy basil (Ocimum sanctum) extract at the concentrations of 0 (control), 100, 200 and 400 mg/kg of feed for 30 days. The treated fish fed the holy basil extract at the 200 mg/kg level showed the significantly (P<0.05) greatest increases in specific growth rate and the greatest improvements in feed conversion ratio. The immune response, phagocytic activity and superoxide anion production were also stimulated the most on day 7 of the feed supplementation. In a streptococcal challenge experiment, the fish fed the holy basil extract at the 100 and 200 mg/kg levels showed 0% cumulative mortality, whereas the control group and the fish fed with extract at the 400 mg/kg level showed 100 and 40% mortality, respectively. The greatest stimulation of the immune response occurred in the fish fed the holy basil extract at the level of 200 mg/kg of diet. Thus, the analysis of the relative expression levels of three cytokine genes, which included interleukin-1 beta (IL-1 beta), interleukin-8 (IL-8) and transforming growth factor-beta (TGF-beta), were compared between a control group and a fish group fed the holy basil extract at the 200 mg/kg level. The expression of all the genes was significantly (P<0.05) greater in the treated than in the control fish, especially on day 7 of the feed supplementation. These results indicated that the addition of holy basil extract to fish feed at the rate of 200 mg/kg of diet could enhance the growth, immune response and disease resistance against S. agalactiae of Nile tilapia during a 30-day supplementation period. (C) 2016 Friends Science Publishers