In fish, sex determination (SD) system shows high variation. The SD mechanisms include environmental and genetic regulation. The research on SD system and related genes in intensively studied fish species was reviewed. Although some genes have been described as sex-related, only DMRT1bY can be considered as a master sex determination gene and none of them has been utilized in aquaculture. The variation of fish SD system, the importance of sex-related genes in evolution research and the relations between environmental factors and sex-related genes were also discussed. The fish sex determination mechanism remains largely unknown. Further research needs to be done considering the significance of fish SD studies in basic and applied aspects.