الفهرس 
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Abstract
This study was undertaken to evaluate the use of spirulina (Arthrospir platensis) as hematological and immunological stimulant for Nile tilapia, Oreochromis niloticus (L.).A total of 270 fish (50±5 g) were randomly distributed into six groups fed on a diet containing 0.0, 5.0 or 10.0 g spirulina/kg diet for 6 weeks. Each subdivided into three equal replicates. After the feeding trial, fish of each treatment were challenged by pathogenic Pseudomonas. fluorescens, which was given by intraperitoneal (IP) injection and they were kept under observation for 15 days to record any abnormal clinical signs and the daily mortality rate. The blood samples were taken after 4 and 6 weeks for hematological and immunological examinations. The hematological parameters were improved when fish fed spirulina supplement. However, the highest red blood cells (RBCs), white blood cells (WBCs), neutrophils, monocytes and basophils were obtained at 5.0 - 10.0 g spirulina/kg diet before and after the infection. There were non significant changes in lymphocytes after 4 weeks, while after infection with Pseudomonas. fluorescens lymphocytes increased in groups supplemented with spirulina. Also, spirulina improved serum biochemical parameters which included, AST, ALT, total protein, albumin, globulin, glucose, creatinine, uric acid and cholesterol in groups supplemented with spirulina. Moreover, spirulina enhanced serum lysozyme activity, bactericidal activity, and antioxidant enzymes (GPx and SOD) of treated groups before and after the infection. Total fish mortality 15-days after IP injection with P. fluorescens decreased with the increase of spirulina level in fish diets. The lowest fish mortality and the highest level of protection were obtained when fish fed 10.0 g spirulina/kg. Histopathogical findings indicated that the supplemented groups with spirulina exhibited hyperactivity of melenomacrophage centers of haemopiotic organs. These results indicate that spirulina supplementation is promising for disease prevention in tilapia culture and the optimum level of spirulina in fish diet is 10.0 g per kg diet.