The aim of this study was to investigate a possibility to decrease a toxic influence of aflatoxin on the fish organism and veterinary-sanitary evaluation of fish, fed by a pure fodder, aflatoxin and ketoconazole+aflatoxin. Fish aflatoxicoses cause essential losses at fish growing using industrial production technologies. It is characterized by decreasing weight gains and increasing kill of commodity fish, worsening fodder conversion. Farmers often use fodders of own production, without conducting laboratory studies, and don’t know about aflatoxins. At the same time because of different reasons, first of all economic ones, they don’t use adsorbents for decreasing the negative influence of aflatoxins on the fish organism. Their use doesn’t guarantee 100 % fish resistance to micotoxicoses and correspondingly product safety for a consumer. Fish, received aflatoxins with food, is dangerous as a food product for humans and animals. Aflatoxins are very stable in the environment, so even thermal processing doesn’t exceed risk of aflatoxin contamination. The article presents a possibility of effective treatment of fish at aflatoxicosis. It is known, that aflatoxin beyond cells is not dangerous. Its activation takes place within a cell by the enzyme system cytochrome Р-450, forming an epoxide, in which result the aflatoxin inclusion complex with DNA forms in the kernel. The veterinary preparation “Ketoconazole” inhibits cytochrome enzymes Р-450, so aflatoxin activation within a cell doesn’t take place, epoxides don’t form, DNA cells are not injured, aflatoxicosis doesn’t develop in fish that has been proved experimentally. The veterinary-sanitary mark of fish, treated for aflatoxicosis, is satisfactory.   The importance of this study is in fact that for today there is no developed effective method of fish aflatoxicosis treatment. An influence of aflatoxin on the crucian organism has not been studied experimentally