Sexual differentiation, neurobiology, and behaviour in the convict cichlid (Cryptoheros nigrofasciatus)

In this thesis, I examined the possibility that phenotypic sex of convict cichlids, Cryptoheros nigrofasciatus, is environmentally determined I also investigated intrasexual variation in sexually dimorphic traits. In the first series of experiments (chapter 2), the body size of a cohort of wild-type convict cichlids was manipulated to establish whether relative body size determines sex in these animals. In this study size did not influence sex. Examination of gonadal tissue at 45 days of age revealed that most animals at this age have female ovarian tissue. This finding suggests that half of the population undergo some form of sexual transformation. In the second experiment (chapter 3) I examined male preference for variation in female-typical orange colouration. Males preferred females with the most conspicuous colouration. Lastly, in the third experiment (chapter 4), sexual differences in gonadotropin-releasing hormone (GnRH) neuromorphology were examined. Manipulations of social status showed a regulatory sexual dimorphism in GnRH soma size.