In the last decade, there has been a shift in the sex ratio of the mussel Mytilus galloprovincialis in the Black Sea towards increase of males. In modern literature, focus is mainly on mechanisms of sex inheritance in mussels and hormonal regulation of the reproduction, and there is no information on sex inversion in M. galloprovincialis under the influence of environmental factors. The goal of this work is to establish the fact of sex change in mussels cultivated near the coast of Crimea under

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... ast of Crimea under the influence of some external environmental factors. We establish that mussels change sex from female to male, but some specimens become hermaphrodites, with their fraction reaching 13%. Under unfavorable environmental conditions, mussel females change sex, and their mortality rises up to 69%. In water areas subject to anthropogenic impact, the proportion of sex inversion in the mollusks may be as high as 58%. The influence of various adverse environmental factors on sex inversion in mussel females is unequal, and its strength decreases in the following order: diesel fuel > hypoxia > anionic detergents > starvation.