Bacteriological study of cultured silver carp (Hypophthalmichthys molitrix) in Gilan province, Iran

The study was undertaken to determine bacterial contamination of warm-water fish ponds and silver carps harvested from those ponds in Guilan province, Iran. In this respect, water samples were taken from 7 ponds and investigated by testing total bacteria, coliforms, and Escherichia coli. In addition, skin swab samples of silver carps caught from each pond were studied for enumeration of the same bacteria as well as Staphylococcus aureus and also for the presence of some human bacterial pathogens including Salmonella spp., Vibrio spp., and Listeria monocytogenes. For all bacteriological examination techniques of International Organization for Standardization were followed. Results showed that mean water bacterial quality in ponds was significantly different (p < 0.01). About 43% of water samples were positive for E. coli, which indicates fecal contamination of some fish ponds. Bacteriological results of the fish harvested from ponds showed significant differences (p < 0.0001) in total bacterial counts and coliform counts. However, counts of E. coli and S. aureus did not vary significantly (p>0.05) in different ponds. Results also showed that potential human pathogens were isolated from about 78.5% of fish studied. Out of five bacteria genera investigated, S. aureus, E. coli, V. cholera, and L. monocytogenes were isolated from 78.57%, 47.61%, 7.14%, and 4.76% of the fish samples, respectively. The Salmonella spp. and V. parahaemolyticus were not detected in fish samples during the study. The association of pathogenic bacteria among silver carps suggests that if fish are handled or prepared improperly it could lead to food safety hazards for consumers.