In an extreme feat of parenting, some female cichlid fish carry their eggs and babies in their mouths for about two weeks. In this way, the young fish and fish-to-be are protected from predators in the outside world. The problem? Some get eaten by their own mothers.
A new study published Wednesday in Biology Letters not only reveals this cannibalism, but it suggests mother fish that eat their own young reduce cell damage caused by mouthbrooding, writes James Ashworth for London’s Natural History Museum.
“The females are gaining something from [eating their young], not just in terms of body condition, but even something that could potentially boost their health,” Peter Dijkstra, a biologist at Central Michigan University and a co-author of the study, says to New Scientist’s Christa Lesté-Lasserre.
Raising young is physiologically demanding for the central African fish, called Astatotilapia burtoni. While mouthbrooding, they can’t eat or breathe properly, writes National Geographic’s Tom Metcalfe.
The study “adds an interesting piece to the puzzle of how these mouthbrooding females are able to survive and maintain their own health during the two-week brooding period when they can’t eat,” Karen Maruska, a biologist at Louisiana State University who studies A. burtoni but did not contribute to the new research, tells National Geographic.
A. burtoni aren’t the only fish that consume their progeny—a practice called “filial cannibalism.” Male barred-chin blenny and common goby fish munch on some of the eggs they’re supposed to be looking after. Guppies, too, eat their own babies. And some insects, birds, reptiles, amphibians and mammals have also been observed eating their offspring, per the Natural History Museum.
The researchers weren’t initially studying cannibalism—at first, they were interested in how mouthbrooding affects the health of female A. burtoni. In a 2019 study, Dijkstra and his colleagues found that the mothers’ bodies produced more chemicals that damage cells while mouthbrooding, New Scientist writes.
In the new study, the researchers looked at more than 60 female A. burtoni. Around half were mouthbrooding, and the other half were not, since the researchers removed their eggs, per New Scientist. After two weeks, 29 of the 31 mouthbrooders had fewer offspring—and their broods had become 40 percent smaller on average, according to National Geographic.
The researchers concluded that the missing offspring had been eaten. “They could have been dropping them, but I observed them every single day for hours and never saw that happen,” Jake Sawecki, a researcher at Michigan State University and the study’s lead author, tells New Scientist. “The only really logical explanation was that they were consuming some of them.”
Doing so might have had health benefits for the mothers, the scientists suggest. Mouthbrooding fish had higher levels of chemicals called reactive oxygen species (ROS), which can damage DNA. The fish that had more of the harmful chemicals also ate more of their offspring. This could have provided them with antioxidants to counteract the imbalance of ROS.
“Mothers can derive nutrients and probably also antioxidants from their babies,” Dijkstra says to the Natural History Museum.
After two days, the mouthbrooders had 23.7 percent more DNA damage in their livers than the fish that were not raising young did. But after six days and again after two weeks, the brooders and non-brooders had similar levels of damage, per New Scientist. Sawecki tells the publication that the findings suggest eating their offspring reduces stress on the mothers’ bodies.
“In the grand scheme of things, it’s probably more beneficial to eat some of those young and be able to reproduce again in the future, rather than to die after that reproductive cycle and only have produced X number of young,” Sawecki says to New Scientist.