Here’s how a species of fish changes sex in 10 days

There are fish that change sex once they become adults, something that may seem bizarre to most people but that is normal for different animal species. However, how fish change sex has never been clear. Now, a new study, published in Science Advances, sought to clarify the modalities of this process, at least as regards a species of fish.

An international group of researchers, led by New Zealand scientists, focused on the Thalassoma bifasciatum, a marine fish of the family of the wrasse which is also known as bluehead wrasse. This fish performs the sex change very quickly and the change itself is triggered by an external signal, as recalled by Jenny Graves, a professor at the University of La Trobe, one of the authors of the study.

The scientist ensures that genes, even after a sex change, do not change so they must be turned off by a signal. The change takes place in particular ways: these fish live in groups composed of females dominated by a single male specimen. If the latter dies or is removed from his “harem”, the largest female in only 10 days becomes male and becomes the leader of the group. His behavior changes in a few minutes while his color changes a few hours. The ovaries become testicles and within 10 days are already capable of producing sperm.

Researchers have discovered that there are specific genes that are deactivated and activated in the brain and gonads of this fish that in turn trigger sex change. The discovery occurred through RNA sequencing and epigenetic analysis. During the sex change, a “complete genetic rewiring of the gonad” takes place, as specified by Erica Todd of the University of Otago, author of the study that adds: “The genes needed to maintain the ovary are first deactivated, and then a new genetic path is constantly activated to promote testicular formation.”