Ability of bacteriological self-purification of common carp, tench and crucian carp fingerlings reared in pond receiving the discharge from sewage treatment plant and then kept in running river water of different quality

Abstract

Studies were carried out on bacteriological self-purification of muscles, skin, and digestive tract contents of common carp (1+), tench (2+), and crucian carp (1+) reared in a pond supplied with a discharge from sewage treatment plant in Jedwabno (Masurian Lakeland) and then kept for 21 days in a concrete pond supplied with the effluents from trout culture, and for another 4 days – in a plastic tank with the Łyna River water. The study was carried out in autumn 1996 on 5 individuals of each species, before and after fish cleaning in running water. The following bacteriological indices were evaluated: total number of bacteria on broth agar at 20 and 37°C, number of coliforms, fecal coliforms, fecal streptococci, Clostridium perfringens, Pseudomonas aeruginosa, Aeromonas sp., and Salmonella sp. No Clostridium perfringens and Pseudomonas aeruginosa were found in the tissues and digestive tract contents of the fish. Fish kept in running water eliminated majority of the bacteria from their tissues and digestive tract. In case of the muscles, however, contents of bacteria remained too high. Total numbers of bacteria on broth agar in 20 and 37°C were only slightly reduced, and numbers of fecal streptococci even increased. On the other hand numbers of coliforms, fecal coliforms, and Salmonella sp. were considerably reduced. Numbers of bacteria in the muscles decreased more in common carp and tench than in crucian carp.