These mother fish eat some of their offspring to maintain strength, study finds

Researchers hoping to learn why African freshwater cichlids carry newborn babies in their mouths discovered something even more bizarre: they devour some of the young offspring in the process.

Even more surprising was that it appeared to be beneficial to the mother's health — and, arguably, the long-term survival of the species.

"The really amazing finding was that we found that the number of babies that a mother had eaten ... was positively linked to their overall health," said Peter Dijkstra, an assistant professor of biology at Central Michigan University and co-author of the study published this week in Biology Letters.

"So those mothers, they had better antioxidant function, and they were just doing better than those that ate fewer of their babies," he told As It Happens host Nil Köksal.

The Astatotilapia burtoni is a colourful, freshwater cichlid fish commonly found in some parts of Africa. They're also known as Burton's mouthbrooder, from the fact that the mothers often keep their babies in their mouths as shelter from the elements.

Researchers observed about 80 cichlid mothers that had recently laid eggs. According to National Geographic, they "delicately" removed all of the fish eggs from each of the mothers' mouths and distributed 25 eggs into about half of the test group's mouths. They then kept the other mothers without any eggs in their mouths as a control group.

They observed the fish as they carried the eggs in their mouths for up to three weeks after they hatched.

It's a little dark, when you think about it.- Peter Dijkstra

Dijkstra found that 90 per cent of the mothers ate "at least some" of their babies over the observation period.

On average, the mothers ate about half of their offspring, Dijkstra said, while some ate nearly 90 per cent.

He said they originally wanted to see how a species of mouthbrooder fish coped with the intense stress of keeping their offspring safe.

"During the brooding ... they cannot eat. They're basically starving themselves," he said. "So it's very tempting for the mothers — you know, like, the babies are already in the mouth. Why not eat a couple? Or maybe even more than a couple?"

"It's a little dark, when you think about it."

It might seem counterintuitive for a mother to consume their young; after all, aren't they supposed to ensure the survival of their offspring, and the species as a whole?

Dijkstra said the evidence may seem "counterintuitive" at first glance, but in fact makes sense over the long run. As the mother cichlid is heavily burdened by mouthbrooding, consuming some — but not all — of her babies helps maintain her health and ensure she will have more children in the future.

"It's kind of like a family-planning type of phenomenon that is going on here," he said.

Dijkstra said that for now, there is only a correlative link between a mother cichlid having a stronger liver health and eating more of its offspring than less. He and his team are continuing their research to learn whether that connection is directly linked.

He noted that it was his student and the study's leader Jake Siwecki that first discovered the phenomenon, rather by accident.

"He actually told me, you know, 'I'm sure I put 25 eggs back into the mouth of the mother, but this mother here, I can only find 10 babies,'" said Dijkstra.

"And then we looked at each other and we were like, well, she probably ate the rest."