An experiment was performed in a twelve weeks period at three varied stocking densities: low density (LD, 100 fish m-3), medium density (MD, 200 fish m-3) and high density (HD, 400 fish m-3) to analyze the biological performances and ingestive behaviour, of Nile tilapia (Oreochromis niloticus) and Lately, fish were challenged with Aeromonas hydrophila to evaluate the cumulative mortality (%). Stocking density had no effect on survival rate, the final weight markedly reduced with increased density, ingestive behaviour was higher in fish reared in MD than fish reared in LD, however, fish at HD have a higher feed intake (%) and feed conversion ratio. Fish at LD showed marked higher levels of total protein, albumin and globulin compared with those reared at HD. plasma glucose and cortisol levels were high in HD contrast to LD and MD groups. LD fish had higher RBCs and WBCs parallel to MD and HD. similarly, lymphocytes, neutrophils, and monocytes (%) decreased with increasing density. In addition, Serum antioxidant and lysozyme enzymes were considerably (P
Key words: Nile tilapia, Biological performances, ingestive behaviour, Physiology, Immune, challenge.