Curious Creatures: Swimming upstream with gender fluid fishes.

Curious Creatures: Swimming upstream with gender fluid fishes.

You are either male or female, a tick on the box that life gives you at birth.

But under the sea, it isn’t as straightforward as that. More than one quarter of fishes on the reef are hermaphrodite creatures, meaning they have both female and male sex organs. Or are able to develop both organs.

In our last post here, we explored the sex change clown fishes undergo when the dominant female in the group dies.

Now, let’s dive a little deeper in other forms of sex change that fishes exhibit. Hermaphrodites are divided into two main categories:

1. Synchronous hermaphrodites.
Synchronous or simultaneous hermaphrodites have both active male and active female sexual organs. And while they do have both sexual organs to function sexually without the help of a partner, self-fertilization is a major no-no. Incest leads to inbreeding, and does not promote genetic diversity. So their solution for this, is to take turns.

During mating, simultaneous hermaphrodites take turn to fertilize each other’s eggs. One individual will play the role of the female and lay the eggs, while the other will take on the male role to fertilize the eggs. After a moment, they will mate again but with the roles reversed.

Examples of Synchronous hermaphrodites fish: Seabass, Hamlet, deep sea fishes.

2. Sequential hermaphrodites.
Sequential hermaphrodites are fishes that start out as one sex and change to another sometime in their life span. This sex change is usually controlled socially. There are two main categories for sequential hermaphrodites: protogynous and protandrous.

Protandrous hermaphrodites are fishes that change from male to female. Polygyny groups have dominant males with multiple females. When the male dies or disappears, the next biggest female in size will take on the role as dominant male.

While protogynous hermaphrodites are fishes that change from female to male, in a polyandry group, there is a dominant female with multiple males and the same happens when the dominant females dies or disappears.

Between the two, protogyny is the most common form of hermaphroditism in fish in nature with about 75% of the 500 known sequentially hermaphroditic fish species are protogynous.

Examples of sequential hermaphrodites fishes: wrasses, gobies, grouper.