Plants and Animals

Some Male Fish Incubate Eggs Fertilized By Others in Their Mouths

Some Male Fish Incubate Eggs Fertilized By Others in Their Mouths

Certain fish species endure weeks without eating in order to securely retain eggs in their jaws. The fact that some male fish do it even when they aren’t the biological parents of the eggs they’re preserving adds a twist to this incredible act of parental care. The reasons behind this, like many other aspects of the process, are unclear. For people who are unable to take evasive action, aquatic surroundings can be harmful. Many fish species have evolved “mouthbrooding,” in which a parent retains the eggs in a position where predators can’t get to them, to protect their eggs from becoming food.

The existence of so many eggs makes it difficult – if not impossible – for the brooder to feed, which has obvious drawbacks as compared to giving birth to live offspring. It does, however, allow for a more equitable allocation of parental effort. Researchers from Charles Darwin University opted to investigate the mouthbrooding mechanism in two northern Australian fish species. The findings were surprising enough to be reported in Biology Letters.

The first author, student Janine Abecia, told IFLScience that male Neoarius graeffei and Glossamia aprion are responsible for egg guarding, as are most mouthbrooding fish. “It appears to be a mechanism for males to impress females,” Abecia told IFLScience, implying that the males are gaining more chances to mate. Take that, everyone who thinks child care is solely a mother’s responsibility. Both fish reside in murky waterways, making it difficult to examine their behavior. The limited observations we have come from tanks, and their behavior in the outdoors may differ. Mud doesn’t hide DNA, so Abecia and her colleagues examined hundreds of individuals of each species to see if the eggs being cared for are the brooder’s offspring.

The results of N.graeffei were as expected: monogamous dads looked after their children. G. aprion, often known as “mouth almighty,” had a different story, frequently caring for the children of another parent. Because mouth-almighty eggs take 4-5 weeks to hatch, that’s a significant sacrifice for the species’ sake, or possibly the pinnacle of Piscean homoeroticism. The guys were sometimes nursing eggs from a variety of parents, including their own and another male. Other men were guarding eggs that had been completely fertilized by another. In some circumstances, the male was carrying eggs that he had fertilized but that originated from many females.

The evolutionary foundation for this, according to Abecia, is unclear. She didn’t look to see if the eggs belonged to a sibling, which may indicate that they were bred together. The male begins accepting [the egg mass] in its buccal cavity when it is halfway out of the female, according to aquarium observations (and the queasy may want to turn away). “We don’t know when fertilization occurs,” Abecia told IFLScience.

Females have even been reported pursuing males and forcing them to vomit up the valuable eggs, maybe to persuade an obviously good spouse to quit caring for another’s eggs and take her own instead. Females also generate “dummy eggs,” which are incapable of hatching and are given to males as a gift, preparing them for the long journey ahead. Mouth almighties have a large gob in comparison to their small stature, as their names imply, but Abecia believes this has as much to do with their role as ambush predators as it does with their reproductive activity.