الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
The purposes of this study was the isolation and identification of some yeast and evaluate their antibacterial effect, growth curve and studing its safety for Oreochromis niloticus. Rhodotorula minuta, Saccharomyces castelli, Zygosaccharomyces sp and two different species of Candida were isolated from intestine of Oreochromis niloticus; Mylopharyngodon piceus; Hypophthalmichthys molitrix and Clarias Garipeneaus muscles respectively. Rhodotorula minuta, Zygosaccharomyces species and Saccharomyces castelli had antibacterial activity against Aeromonas hydrophila, Aeromonas veronii, Aeromonas sobria, Aeromonas jandaei, Pseudomonase anguilliseptica and Pseudomonas fluorescence. Saccharomyces castelli was harmless to experimentally infected O. niloticus, while Zygosaccharomyces species and Rhodotorula minuta were pathogenic to O. niloticus at 0.2 ml ×105 cells/ml by intraperiteneal injection (I/P). The mortality rate was 57.1 and 42.8% respectively in comparison to the control and Saccharomyces castelli groups, which the mortalities were 30 and 15.8% respectively.
The stationary phase of yeast was at the 5th and 6th day of growth with Saccharomyces castelli and Rhodotorula minuta while Zygosaccharomyces at 7th and 8th day. Higher viable cells were recorded at 4oC storage and the number was declined by increasing storage time while the number of food stored at 25oC declined and decreased monthly.
Two hundreds and twenty five apparently healthy O. niloticus (20 ± 3 g average body weight) were assigned randomly to five groups; each group in three replicates (15 fish per each replica). Dead Rhodotorula minuta and live Saccharomyces castelli were added to commercial feed (crude protein 30%) in two different dosages (5 and 10 g of yeast / kg diet) and fed Nile tilapia to evaluate its effect as immunostimulant and growth promoter. The fish were fed twice daily until satiation for 28 days. At the end of experimental period, the fish was challenged intraperiteneal with Aeromonas sobria and Pseudomonase fluorescens and kept under observation for 14 days. Dead Rhodotorula minuta and live Saccharomyces castelli in the different doses had a significance increased in the growth parameters, heamatocrite value, respiratory burst, lysozyme activity and serum bactericidal activities. Also they decreased viable bacterial count in intestine and increased antibody titer of A. sobria and Ps. fluorescence antigen than control group. The y*easts increased the relative level of protection against Aeromonas sobria and Pseudomonas fluorescence in Nile tilapia. So the live cells of Saccharomyces castelli and dead cells of Rhodotorula minuta enhanced growth, immune response and resistance of O. niloticus against A. sobria and Ps. fluorescens.