Neuroendocrine regulation in sex-changing teleost fishes

Certain fishes undergo a truly fascinating transformation in which they change sex from female to male, or vice versa. To the layman, this idea is most likely mind boggling. To the initiated researcher, this idea presents a plethora of interesting research opportunities.

Teleost fishes display the greatest diversity of reproductive strategies of any vertebrate class. They exhibit internal and external fertilization, oviparity, and viviparity. The variety of reproductive modes includes such diverse strategies as sex reversal, simultaneous hermaphroditism, parthenogenesis, sexual parasitism, and self-fertilization (Zaitsev et al., 1967). The strategy that is most common throughout the animal kingdom, gonochory (separate sexes), is also common in teleosts. While all these modes of reproduction are worthy of discussion, this chapter discusses the process of sex change in fishes, and specifically its neuroendocrine regulation. Sex change, one of the best examples of phenotypic plasticity found in the animal kingdom, is a complex phenomenon that covers multiple aspects of many neuroendocrine axes. There are few parts of the neuroendocrine system that are idle during, or untouched by sex change.

Here we explain the different types of sex change occurring in fishes, as well as the main hypotheses explaining this phenomenon. We then discuss the roles of the various components of the neuroendocrine system over the course of sex change. For clarity's sake, these components are divided across three chronological stages: (1) stable social environment, (2) rapid brain changes in a permissive social environment, and (3) gonadal remodeling and feedback to the brain. Finally, we look at the latest methodological developments in the field.