Production of all-female cod as a means to circumvent problems with early puberty in males: Studies on sex determination and differentiation

Early puberty is a major problem in cod farming both due to negative impact on production performance in on-growth farms, and due to risk of negative genetic impact on wild stocks following spawning in sea cages or after escape. Use of all-female stocks c an mitigate some of these problems. However, no information is available on the sex determination mechanism in Atlantic cod, the timing of sex differentiation, or the susceptibility to exogenous hormone treatments for inducing sex reversal. Thus the curre nt projects aims to reduce problems connected with early puberty in male cod by developing the basic knowledge required for the production of all-female populations. Specifically, it will attempt to identify the nature of the sex-determining system in cod by: 1) Studying karyology with a complementary range of cytogenetic techniques to determine if the genotypic sex can be recognized directly, and by inducing gynogenetic development to recognize the sex determination system indirectly. 2) Describing the t iming of sex differentiation in cod by profiling the expression of genes involved in this process in other vertebrates, such as P450 aromatase, Anti-Müllerian Hormone and Dmrt-1 by quantitative real time PCR and/or by in situ hybridisation, and by histolo gical examination of gonadal sex differentiation including - if required - the quantification of germ cell proliferation via immunohistochemical detection of an endogenous proliferation marker (phosphorylated histone-3). 3) Testing the sex reversing effec ts of exposure to androgens in putative sensitive time windows, as deducted from the results on sex differentiation, in order to establish optimal timing, dosage, and way of administration of androgens to produce neo-males.