Reduction of bacterial contamination of common carp under various rearing conditions

Abstract

Numbers of bacteria identified on broth agar in 20 and 37°C, coliforms, fecal coliforms, fecal streptococci, anaerobic sulfite-reducing Clostridium perfringens, Pseudomonas aeruginosa, Aeromonas sp., and Salmonella sp. were evaluated in the muscles, skin, and digestive tract content of common carp (Cyprinus carpio). The fish were sampled: 1. from a pond supplied with biologically purified sewage from a sewage treatment plant in Jedwabno (at the age 1+), 2. after 6 months of wintering in an earthen pond supplied with clean lake water, and 3. after subsequent 6 months of rearing in the same water. Wintering and subsequent rearing took place in the Stocking Material Production Centre in Warlity. The fish were aged 2+. Muscles, skin and digestive tract contents of all fish were free from Clostridium perfringens, Pseudomonas aeruginosa. Salmonella sp. were present only in muscles and skin of fish from sewage-supplied pond. Wintering caused considerable reduction (90.0-98.8%) of coliforms, and fecal coliforms (98.7-100%) in the tissues and digestive tract contents. Numbers of Aeromonas sp. in skin were reduced by 91.1% and concentration of fecal streptococci in the guts - by 74.6%. Further reduction of bacterial contamination was observed after another 6 months of rearing in the pond supplied with clean lake water, but numbers of Aeromonas sp. in the digestive tract increased considerably.