ABSTRACT
Sex determination refers to that event which compromises bipotential gonad to develop as an ovary or a testis (Hayes et al., 1998). Fishes are characterized by a level of sexual plasticity that is unrivalled among other vertebrates. They display most divergent expressions of sex. The range of morphotypes encountered within a sex is astounding (Mank and Avise, 2006a); for instance, genetic morphotypes reported within a species are primary and secondary males (all diandric protogynous hermaphrodites, e.g. Thalassoma bifasciatum), parental and cuckolder (e.g. blue-gill sunfi sh, Lepomis macrochirus), hooknose and jack (e.g. coho salmon, Onchorhynchus kisutch), pairing and haremic males (e.g. the Nigerian cichlid Pelvicachromis pulcher) and phenotypic morphotypes are the streaker, satellite, sneaker and piracy males (e.g. shell-brooding cichlid Telematochromis vittatus). Whether these morphotypes represent the expression of alleles of the same sex determining gene(s) or different genes operate to determine these male genotypes is not known. In O. tshawytscha, sneaker males are known to sire sneaker sons (Heath et al., 2002).
