Abstract: The bacterial flora occurring in pond water,surface mucus,gills,intestine and putrid meat of healthy tilapia cultured in freshwater,were estimated both quantitatively and qualitatively.The results showed that total viable count of bacteria in above samples respectively were 2.6×104 CFU/ml,1.0×103 CFU/cm2,2.2×103 CFU/g,1.4×105 CFU/g and 5.4×107 CFU/g.Total 353 isolates were dominated by Gram-negative bacteria.Bacillus sp.,Enterobacteriaceae sp.and Vibrionaceae sp.were predominant in pond water and fresh fish,with a small number of Pseudomonas sp,Enterococcus sp.,Staphylococcus sp.and so on;but the dominant position were changed with different samples.The bacterial flora were simple in putrid meat,Pseudomonas cepacie,Aeromonas hydrophila and Bacillus brevis were dominant spoilage organism,with a small number of Edwardsiella tarda and Kluyvera spp.In addition,GB and SN standard methods were used in detecting the pathogens on surface mucus,gills and intestine of newly-harvested tilapia,Escherichia coli,Pseudomonas aeruginosa and Streptococcus faecalis were detected,but Listeria monocytogenes,Salmonella sp.,Staphylococcus aureus,Vibrio parahaemolyticus and hemolytic streptococcus were not detected.

Key words: tilapia, bacterial flora, pathogens, spoilage bacteria