Fish Gonadogenesis. Part I: Genetic and Environmental Mechanisms of Sex Determination

Many species of fish produced in aquaculture or for the ornamental fish trade exhibit sexual dimorphism in growth, age at maturity, secondary sexual characters, or other traits of interest. This has led to a desire to produce populations of only one sex for commercial on growing. Although direct sex reversal via manipulation of sex differentiation is used commercially (e.g., in tilapia aquaculture), in most cases there is a need to understand the sex determination system to some extent and manipulate this to produce monosex fish. Sex determination is the genetic or environmental process that establishes the sex (gender) of all organism, whereas sex differentiation is the process by which all undifferentiated gonad is transformed into apt ovary or a testis. Fish are the most diverse group of vertebrates in terms of sex determination. and the number of fish species of interest to aquaculture keeps increasing. Together these aspects explain the growing interest to understand how sex determination and differentiation produce the sex ratio. This review concentrates on recent research using the tools of molecular biology to broaden our understanding of the different aspects related to fish sex determination, both in model fish species and in species of commercial importance.