This study was carried out to indicate the toxigenic fungi of cyprinids and aquatic environment at fish farm in northern Iran. For the determination of toxigenic fungi infestation of three fish species (Common carp, Grass carp and Silver carp) samples were obtained from skin, gills and their ponds water. Four species of toxigenic fungi were isolated that included:
Aspergillus flavus (6.2%), Alternaria spp (33.8%), penicillium spp (4 1%) and Fusarium spp (19%). There was a significant correlation between the level of contamination of skin and gills among fish being studied.
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