Rewrite the article and explain the process of mouthbrooding in a simple way, so primary school children can understand it.

Why these fish mothers cannibalise their babies

Some African cichlid fish raise their young in their mouths—and snack on them. Now, scientists may have figured out the reason.

Raising babies can be exhausting—so much so that some mouthbrooding mothers snack on their young, according to a new study.

A central African cichlid fish, Astatotilapia burtoni—commonly called Burton’s mouthbrooder—sometimes consumes more than three-quarters of their own eggs and baby fish.

“It is a surprise,” says Peter Dijkstra, a biologist at Central Michigan University and senior author of a study published today in Biology Letters. “It really is a lot.”

Mouthbrooding is common among fish, particularly cichlids, colourful freshwater species that are popular as aquarium pets. After their eggs are fertilised, A. burtoni mothers will shelter them in their mouths for roughly two weeks to protect them from predators. (Read about other long-haul animal mothers.)

After the eggs hatch into tiny larval fish, the babies venture outside their mother’s mouth, but scurry back in when there’s danger. It’s a great start for the young fish, but it’s extremely tiring for the mother cichlid, who can’t breathe properly or eat during that period.

The new study shows, however, that the suffering moms can counter that by consuming some of their young, a behaviour called “filial cannibalism.”
A biologist called Peter Dijkstra has done a study into a colourful fish called the African cichlid fish. This fish lives in Central Africa, but some people have it in their aquariums.

The African cichlid fish keeps their babies in their mouths after they are born. The mother's mouth is like a bird's nest or a fox's den. After the eggs hatch into tiny baby fish, the baby fish are vulnerable and they need a safe place to live, so they don't get attacked by predators. The babies live in their mum's mouths for two weeks. This is called mouthbrooding.

The baby fish swim outside their mother’s mouth, but if there is any danger they go back in and hide. It is a great start for the baby fish. However, it is not good for the mothers. It makes the mother fish very tired. In fact, they can't breathe well with the babies in their mouths. They can't eat because their mouth is full of their babies and eggs. This is why they sometimes eat some of their eggs and babies. They sometimes eat more than three-quarters of their own eggs and baby fish. 

Scientists are very surprised about this. 