Ray-finned fishes (Actinopterygii) is a very diverse and numerous clade of vertebrates. Besides the diversity of ecological niches and morphology, species of this clade have substantial differences in mechanisms of sex determination. Unfortunately, our modern knowledge about sex determining mechanisms is limited to a small number of species. Even from the modest number of published works on this topic it is obvious that evolution of sex determining system in ray-finned fishes is very plastic: in some closely related species sex systems can be significantly different, there are taxa with quite conservative systems, and the same genomic loci may play sex determination role independently in various groups. Such diversity allows considering ray-finned fishes to be used as a convenient model taxon for researching emergence and development of different sex determining systems.