| Summary: | The objectives of this study were to investigate the effects of Oliveria decumbens as a medicinal herb with reported immunostimulatory potential on the growth, immunity status and health of Nile tilapia (Oreochromis niloticus). In an eight- week trial, fish (45 ± 5 g) were randomly divided into 13 treatments as follows: in 10 treatments fish were fed on diets containing 0 (control), 0.01, 0.1 and 1% of O. decumbens extract and essential oil and their 1:1 combinations. Also, in three treatments fish received plant hydrolate at doses of 312.5, 625 and 1250 ppm as bath treatment. At the end of experiment, blood samples were taken for immunological and biochemical measurements. All treated fish showed comparable growth performance to those received control diet. The highest levels of respiratory burst activity were observed in extract 1% group. Similarly the serum lysozyme levels were significantly affected by essential oil and extract supplemented diets. Fish received plant hydrolate at dose 312.5 ppm showed the highest significant protein level. Also, the globulin levels were increased in group fed on diet containing extract 1%. Plant supplementation had no negative effects on the fish health biochemical indices including cholesterol, triglyceride, alkaline phosphatase and aminotransferase enzymes. In conclusion, the results of this study showed that application of O. decumbens derivatives improved the immunity of Nile tilapia without adverse effects on fish growth and health.
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