8 th International Symposium on Tilapia in Aquaculture 2008 1073 EFFECT OF SOME IMMUNOSTIMULANTS ON HEALTH STATUS AND DISEASE RESISTANCE OF NILE TILAPIA (OREOCHROMIS NILOTICUS) NEVIEN K. M. ABDELKHALEK 1 , VIOLA H. ZAKI 2 AND M. A. A. YOUSEF 2 1. Present address: Laboratory of Marine Biochemistry, Faculty of Agriculture, Kyushu University, Japan. 2. Department of Internal Medicine, Infectious and Fish Diseases, Faculty of Veterinary Medicine, El Mansoura University, Egypt. Abstract Different immunostimulants were investigated to detect changes in the activity of innate non-specific immune response, disease resistance and growth performance of Nile Tilapia Oreochromis niloticus. In this experiment, fish fed on diets supplemented with levamisole HCl (225 mg/kg diet), Immunoton ® (a mixture of vitamins E (150 mg/kg diet) and C (101.2 mg/kg diet) and control diet for 2 weeks. Total leukocyte count (TLC), Differential leukocyte count (DLC), phagocytosis have been measured as indicators for cellular innate immune response. Lysozyme and protein electrophoresis have been measured as indicators for humoral innate immune response, in addition to immunocompetence assay against Aeromonas hydrophila and growth performance test. The obtained results indicated that, addition of levamisole HCl to the diet of O. niloticus significantly enhanced both cellular and humoral innate immune responses and increased resistance to A. hydrophila infection although they had a little growth promoting activity. While addition of vitamins C and E to O. niloticus higher than the requirements needed for growth lead to maximum growth compared to levamisole but little enhancement of the immune response as well as resistance to A. hydrophila infection. Key words: Immunostimulants; Innate immune response; Oreochromis niloticus. * Corresponding author Nevien Kamel Mohamed Abdelkhalek, PhD Laboratory of Marine Biochemistry, Department of Bioscience and Biotechnology, Graduate School of Bioresource and Bioenvironmental Science, Kyushu University, Fukuoka 812-8581, Japan. Tel: +81-92-642-2894 Fax: +81-92-642-2897 mobile: +81- 90- 8404-8906 E-mail. nevien_k@agr.kyushu-u.ac.jp