| Channel catfish is a kind of famous fresh water fish which comes from America. Channel catfish fillet is an important byproduct of channel catfish, and now play an important part in the export of fresh water fish. For this reason great attention has been taken in the security of channel catfish fillets. However, channel catfish is vulnerable to the microbial contamination in the post-harvest handling, processing, storage and sales processing, thereby affecting food quality and safety. In this paper, culture water, freshly caught fish in culture water and channel catfish fillets were selected as experimental materials. The water-quality was analyzed by monitoring pH, dissolved oxygen, total nitrogen, the total phosphate and NO2-N of culture water. The change of the microbiological production of channel catfish fillets were analyzed through quantitative data of total bacteria, bacteria flora and pathogenic bacteria in the sample of culture water. The results were as follow:1. The quality of culture water for channel catfish was studied. The results of the physicochemical parameters in culture water showed that the temperature (19～25℃and 7～14℃), pH (7.2～8.4), dissolved oxygen (6.5～8.4 mg/L and 6.2～12.7 mg/L), total nitrogen (0.4～1 mg/L and 0.2～1.1 mg/L), the total phosphate (0～0.04 mg/L and 0～0.03 mg/L), NO2-N (0～0.4 mg/L and 0.1～0.4 mg/L), which basically reached the requirements of Water Case II, and met the farming standards of fresh water fish.2. Bacteria flora of culture water and freshly caught fish from different breeding bases were studied. The results showed that bacteria flora of culture water and freshly caught fish had difference in different breeding bases. Plesiomonas, Aeromonas, Pseudomonas, Enterobacteriaceae, Bacillus, Brevibacillus, Staphylococcus, Micrococcus, Staphlococcus and Rhizobium were isolated from culture water and fish body of breeding base A. However, there were Xanthomonas and Enterococcus in the sample of culture water and fish body from breeding base B. Enterobacteriaceae, Bacillus and Vibrionaceae were predominant in culture water. The count of bacteria of culture water was closer to that of the surface of fish, but the total number of bacteria of fish gills colony was higher. The total number of Coli form of surface mucus was much lower than that of fish farming water. There were few Pseudomonas spp. and Streptococcus spp. in freshly caught fish.3. The predominant bacteria and pathogenic bacteria of different channel catfish were studied. The results showed that the predominant bacteria had some difference in different parts of fish body. Enterobacteriaceae, Bacillaceae and Staphylococcus were predominant flora of surface mucus, Enterobacteriaceae, Bacillaceae and Rhizobium were predominant flora of gills, Enterobacteriaceae and Bacillaceae were predominant flora of intestine. With the affecting of microbe in culture water, Staphylococcus aureus was not detected in different parts of fish which caught in breeding base A, but it was detected in surface mucus and gill sample of channel catfish from breeding base B. Fecal streptococci were detected in a small amount from culture water and freshly caught fish, Pseudomonas aeruginosa were only found in the surface mucus of channel catfish. Listeria mono cy to genes, Salmonella, Vibrio parahaemolyticus and Streptococcus hemolyticus were not found in channel catfish caught in two breeding base (A and B).4. The change of total bacteria, the proportion and quantity of predominant bacteria and pathogenic bacteria were investigated during the production of channel catfish fillets. The results indicated that the total bacterial counts decreased gradually during the processing of catfish fillets. A total of 1063 and 843 strains of bacteria isolated from the sample of channel catfish fillets caught from two bases were analyzed and compared. The study revealed the Gram-negative organisms, as a group, were more predominant. Enterobacteriaceae spp. and Bacillus spp., and Vibrionaceae spp. were still the predominant flora during the production, but the dominant position was different as the change of different samples. Staphylococcus spp., Micrococcus spp.and Streptococcus spp. got a better effect in killing after Ozone water immersion. Compulsory hygiene standards should be strictly enforced as the processing of manual exposure may be easily infected again. Listeria monocytogenes, Salmonella, Vibrio parahaemolyticus and Sstreptococcus hemolytic were not detected during the processing, and Pseudomonas aeruginosa was found in a few samples in the processing of manual exposure which were followed by the washing and Ozone water immersion.
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