This article presents the research aimed at studying the effect of mycotoxin DON on the structural organization of the liver of common carp. As a result of the studies of the food basis of aquatic organisms, the mycotoxin DON was identified in the feed, under the effect of which the protein-water-electrolyte metabolism was disturbed in the liver cells of the common carp (Cyprinus carpio), which led to hydropic degeneration. This indicates an adverse anthropogenic effect on commercial fish.