Few sights in nature are more heartwarming than that of a mother caring for her young — unless that nurturing act ends with an episode of cannibalism.
Female cichlids — fish in the family Cichlidae — are mouthbrooding fish, carrying their young in their mouths first as eggs and then as hatchlings. As the young fish, known as fry, grow inside their mother's maw, she is unable to eat. And when cichlid moms get hungry enough, they sometimes eat their own offspring, scientists recently discovered.
Researchers from Central Michigan University discovered the gruesome behavior while studying schools of Astatotilapia burtoni, a species of African freshwater cichlid, in their lab. In a study published Nov. 9 in the journal Biology Letters, the scientists reported that in some instances, ravenous A. burtoni mothers swallow some of their young, turning to filial cannibalism as an alternative to starvation.
"It was a complete accident that we discovered their cannibalism," study author Peter Dijkstra, an assistant professor of biology at Central Michigan University, told Live Science.
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Dijkstra and his colleagues first suspected that something was amiss with their cichlid mothers when they noticed that some of the eggs in one female cichlid's mouth were missing. (The fish can hold up to 100 eggs at once, but in this case, the female was carrying only 25 eggs.)
"We realized that one of the mothers wasn't holding all of her offspring," Dijkstra said. "We figured that she probably ate them. There's actually quite a bit of literature out there about cannibalization. It's very common in a lot of animal species."
But why would a mother chow down on her babies?
The researchers said it likely is because females become desperate for nutrients while they're mouthbrooding.
"We think that the females eat the babies to gain something, such as calories," Dijkstra said. "We also believe it's a way for them to gain antioxidants, so the mothers will sacrifice some of their babies to help boost their own health. This could be a way for them to spawn again in the future."
Mouthbrooding also can be a high-stress time for female cichlids, and a prior study of A. burtoni, published in 2020 in the open-access journal Genes, Brain and Behavior, found that high-stress environments can lead mouthbrooding females to cannibalism. In the new study, the authors discovered that some mouthbrooding mothers showed signs of liver damage, with levels of DNA damage that were 24% higher than in non-brooding females.
Gruesome as it may sounds, filial cannibalism is actually a beneficial strategy for reproduction.
"As a parent — and this is also true for humans — you don't want to spend all of your energy on one child," he said. "You want to make sure that in the future maybe you will have more children and you still want to be in good enough shape to take care of your existing children as well. So, it's more like a long-term perspective to family planning."
It's not only cichlids that exhibit this baby-gobbling behavior. Many different types of animals engage in filial cannibalism, including numerous fish species, birds, insects, spiders and even some mammals, Live Science previously reported.
