Last year’s publication of an updated list of fish sex chromosomes describing the huge variation in different types of sex determination in fish has captured notable attention of the biology and biochemistry community. The work showed that the most well-known XY sex-determination systems, involved also in the determination of sex in humans, and their derivatives have a lower rate of degeneration than the ZW systems. They are therefore more malleable and leave more room for evolutionary processes. The database, created by the scientists from the Institute of Animal Physiology and Genetics CAS in collaboration with colleagues from the University of São Carlos in Brazil, provides fundamental information in the field of evolutionary biology that can be used in conservation genetics and aquaculture as well.