Chalk bass are more committed to their spouse than their gender. A new study shows the monogamous hermaphrodite fish switch genders up to 20 times a day.

The sexual flexibility allows the pair to share the reproductive burden more fairly, researchers say. The fish are able to fertilize as many eggs as the pair produce.

"Our study indicates that animals in long-term partnerships are paying attention to whether their partner is contributing to the relationship fairly -- something many humans may identify with from their own long-term relationships," Mary Hart, an adjunct professor in the biology department at the University of Florida, explained in a news release.

Because both chalk bass can produce eggs, couples partake in a competition of sorts to encourage one another. The fish know if they slack off, their mate will too. To push their partner to make more eggs, they themselves must make more.

Chalk bass, Serranus tortugarum, are found among coral reefs off the coast of Panama. A team of Florida biologists spent six months monitoring the fish. During the study, all of the chalk bass pairs remained together.

Monogamy is rare in the animal kingdom, and especially among fish. It's even rarer among fish that live in a high-density social group.

"I found it fascinating that fish with a rather unconventional reproductive strategy would end up being the ones who have these long-lasting relationships," said Andrew Kratter, ornithologist with the Florida Museum of Natural History. "They live in large social groups with plenty of opportunities to change partners, so you wouldn't necessarily expect this level of partner fidelity."

Researchers believe for chalk bass, monogamy reduces the risk of ending up with a partner who produces fewer eggs.

The system isn't perfect, however. Researchers found that 20 percent of the time, a couple ends up with an uneven number of eggs. When that happens, a couple will share their excess eggs with another couple.

Scientists published the new findings in the journal PLOS ONE.