In real life, Nemo’s dad “would have to start behaving as a female just a few hours after Nemo’s mom was eaten by a barracuda.” That’s because his species clownfish (of the genus Amphiprion) are protandrious hermaphrodites, modulating their gender as required to sustain their adult breeding pairs. Practical!

This is just one of the many things we just learned from Deep Sea News, where Luiz Rocha, fish biodiversity expert and curator of Ichthyology at the California Academy of Sciences, spills the juicy details.



Now the wrasses are famed for their gender modulating, and it’s all about being top dog in a polyamorous group.

In these fishes, sex change is controlled socially: a dominant male usually controls a harem of females, and when the male dies the most dominant female in the harem becomes a male. Sex change happens in stages. First, just a few hours after the male goes missing, the dominant female starts behaving as a male. This behavioral change triggers hormonal shifts that cause her gonads to become male gonads and her colors to change into male colors. The entire process is completed in just a few weeks.

The most romantic and ceremonial of fishes are the Caribbean Hamlets.

They are simultaneous hermaphrodites, which is to say that every individual is both male and female at the same time. But to avoid self-fertilization (which is bad because it decreases the genetic variability of the offspring), they trade roles in a strategy known as “egg trading”. After meeting in the same familiar spot in the reef (let’s call it the “bedroom” rock), the pair of hamlets rises in the water column and a mesmerizing spawning event happens: the fish acting as a male embraces the one acting as a female while releasing sperm, and the fish behaving as a female releases eggs. The embrace lasts a few seconds and the pair goes back down to the reef. A few minutes later they rise again, but now the roles are reversed! This fantastic courtship and spawning behavior is easy to observe in shallow reefs of the Caribbean and happens every day during a very romantic time (just before sunset).

The more you know. (Photo: WikipediaLuiz Rocha)