The Truth About Nemo’s Dad: Sex-Changing Behaviors in Fishes

Abstract

Thus far, I have provided evidence in mammals, birds, and reptiles that mammals may adaptively skew sex ratios of offspring and that mechanisms exist by which this may occur. In fishes, there is virtually no evidence showing parental manipulation of sex ratios, perhaps because many fish species exhibit a higher level of plasticity within their sex-determining systems. We now know that fish exhibit the most diverse range of sex-determining systems, ranging from strict gonochorists to hermaphrodites, some with clear genetic mechanisms of sex determination and others with little or no clear genetic influence. In some cases, individuals maintain ovarian and testicular tissue simultaneously through adulthood, choosing whether to produce sperm or eggs in a given attempt. In this chapter, I introduce the many systems of sex determination found in fish species, highlight the environmental and social influences shown to influence piscine sex ratios, and discuss potential adaptive mechanisms of sex allocation in these systems.