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Abstract
This study was conducted to investigate the antibacterial effect of aqueous and ethanol, extracts of Spirulina platensis and Nigella sativa on some fish pathogenic bacterial Gram-negative bacteria (Aeromonas hydrophila , A. sobria , Flavobacterium columnare , Vibrio paraheamoliticus,) Gram-positive bacteria ( Enterococcus fecalis and Streptococcus dysgalactiae ). And evaluate the effect of Spirulina platensis, Nigella sativa and both of them at rate (0.75%, 0.5% and mix of them ) respectively as feed additive for 8 weeks on growth performance, blood picture and immune system in Oreochromis niloticus (O. niloticus) before and after challenge with A. hydrophila .and resistance against Aeromonas hydrophila and Streptococcus dysgalactiae. The results obtained revealed that aqueous extract of Spirulina platensis and Nigella sativa has no antibacterial effect on both Gram-positive and negative bacteria. Ethanol extract of Both Spirulina platensis and Nigella sativa have antibacterial effect E. faecalis and St. dysgalactiae as well as V. parahemolyticus, Fl. columnare, A. hydrophila and A. sobria).Besides E. faecalis was more sensitive to ethanol extract than other bacteria . and The results also indicated that the addition of Spirulina or Nigella to diet improve growth performance, health condition, enhancement cellular and humoral immune responses, specifically (phagocytic activity, lysozyme, nitric oxide, total protein and its fraction especially Þ globulin) either before and after challenged tests and increase resistance against bacterial infection. The combination of Spirulina platensis and Nigella sativa showed the highest values of growth performance, immunological parameters and give the lowest mortality percent against bacterial infection