It is shown that one of the main reasons for the reduction of fish stocks in natural waters is a violation of natural reproduction and one of the most important factors of this process is the impact of toxicological factors, the effect of which also adversely affects the functioning of hatcheries for the reproduction of valuable fish species for introduction into natural waters and for industrial fish farming. The results of studies on the comparative toxicoresistance of fish used in aquaculture, in early ontogenesis to test substances reflecting the main types of pollution of water bodies showed (sulfuric acid, sodium hydroxide, copper sulphide, ortho-cresol, sodium chloride, meat-peptone broth) that the action of these test substances on the incubated eggs, larvae and fish of the family of carp, salmon and whitefish, established a pattern, namely: under the action of all toxicants, in addition to sodium chloride, fish, caviar and carp larvae are most stable, salmon occupy an intermediate position, and whitefish are the most sensitive in the acute and chronic experiments. The peculiarities of the influence of test substances. Scientifically based preventive measures are proposed.