This Fish Can Change Sex 20 Times A Day, But Strangely Remains Monogamous

This native Caribbean fish can change sex faster than your daily mood swings. But despite that, it remains faithful to one mate.

Hermaphroditism is a trait found in species that posses both male and female reproductive organs. Although monogamy and hermaphroditism are common in fishes, both traits in one organism make the chalk bass quite uncommon.

A new research published in the journal Behavioral Ecology suggests that chalk bass (Serranus tortugarum) may only be three inches small, but it can change sex up to 20 times a day.

"I found it fascinating that fish with a rather unconventional reproductive strategy would end up being the ones who have these long-lasting relationships," Andrew Kratter, an ornithologist with the Florida Museum of Natural History told United Press International.

"They live in large social groups with plenty of opportunities to change partners, so you wouldn't necessarily expect this level of partner fidelity," he added.

An article by Leonard Ho, published in the journal Reef Scapes, notes that there are two types of hermaphroditism--the synchronous or simultaneous hermaphrodite, wherein an organism possesses both active male and active female reproductive organs at the same time, and sequential hermaphrodites, wherein an organism possesses both male and female reproductive organs, but only one is active at a given time.

The chalk bass is a simultaneous hermaphrodite. Mary Hart, the lead author of the study, told National Geographic that they have not figured out why the chalk bass changes sex so many times, but hypothesizes that the act may result in a reproductive advantage for the chalk bass.

Since these fish do not self fertilize, the sex switching offers each fish a return on their investment on eggs and cooperative partnership by allowing them to fertilize about as many eggs as they both produce. 

The technique is called "egg parceling," which the study defined as "trading sex roles with the same mating partners in repeated spawning bouts".

In addition, the study revealed that chalk bass pays attention to the amount of eggs being exchanged. For example, if one partner lacks eggs, the other will simply match whatever it produces.

Hart and Kratter, who are actually a couple, spent six months studying the chalk bass behavior at the Smithsonian Tropical Research Institute in Panama. They were surprised how devoted chalk bass are to their partners.

"We did not witness any 'break-ups' in our long-term pairs; during each monthly census, all identified pairs were found spawning and courting with their "primary" mating partner until one or both of them disappeared," the study said.

With only at most five percent of animals known to live monogamously, this is a rare find. The study may prove that sexual cooperation exists among fish.

The International Union for Conservation of Nature lists the status of the chalk bass as "least concern. This fish has a depth range of two to 400 meters, but is usually recorded in less than 90 m. They are often found in aggregation on rubble, silty or sandy bottoms around the immediate periphery of reefs.