The fish is ready to fast, 'raise other boys' just to… girls!

Nestled among the moss in Australia's ponds and streams is the 'Mouth almighty' - a special fish with large and powerful jaws that can catch passing prey. But not only that, male Mouth almightys also use their almighty mouth to shelter hundreds of young.

Mouth almighty fish with a wide mouth and strong jaws.

Oral incubation in fish is known as 'Mouthbrood' and in Mouth almighty it occurs in males at a frequency of 2-3 times/week. Like other Mouthbrood fish, Mouth almighty must expend a lot of nutrients each time it performs oral incubation. It was thought that this would make Mouth almighty fish become shy about raising young, but surprisingly, according to a study recently published in the journal Biology Letters, Mouth almighty fathers sometimes nurse their young. young is not his child.

Janine Abecia - lead author of the study and a PhD student at Charles Darwin University (Australia), where she is studying Mouth almighty and the blue catfish Neoarius graeffei. Both species mentioned above live in freshwater habitats of Australia and belong to the species Mouthbrood. Research also shows that these two species do not eat at all during the process of sucking the eggs.

 'I looked at the stomachs of mouthbrooders and found them to be empty,' Abecia said.

Moreover, having the young with their mouth full can also cause breathing difficulties and slow the movement of the brood, making it difficult to hide from predators. With these disadvantages, according to the laws of evolution, the Mouthbrood species will only take care of their own offspring. However, that is not the case.

The inside of a male Mouth almighty fish's mouth is not always his own.

Abecia collected Mouth almighty and blue catfish from rivers in the Northern Territory of Australia. She also found adult fish with no juveniles left in her mouth for genetic comparison. Abecia then selects about 10 eggs or juveniles from the male fish's mouths and analyzes the DNA to find their lineage.

The results showed that, with blue catfish, 9 fathers are all raising their children and those fry all have the same mother. However, inside the mouth of the Mouth almighty fish, things are a bit strange. Of the 15 litters she brought back from the wild, Abecia said, there are four groups of heterogeneous origins.

Specifically, 2 out of 15 litters had multiple mothers, indicating that the male was flirting with a female once she had an egg in her mouth. A litter had multiple fathers, possibly because another male had surreptitiously fertilized some of the eggs before the father had incubated the eggs. And in another litter, the young were completely unrelated to the fish that were raising them.

Before that, scientists also discovered that some mouthbrood fishes carried the wrong baby. In one type of cardinalfish, about 8% of the parents nurture offspring that are not bloodied. In addition, a study on a fish called Silver arowanas showed that 2 out of 14 broods were carrying 'out-of-species' children.

Obviously rearing juveniles that are not related to the same bloodline is more detrimental to mouthbroods, so why don't the fish seem to avoid this at all?

One possibility is that a mouth full of juveniles makes the male look more attractive.

Male Mouth almighty fish try to impress the female with a mouth full of young, even though it's not their own.

Indeed, Abecia explains: 'Some females are attracted to males taking care of females because they look more trustworthy. Thus, the efforts of the males to 'feed others' now can be compensated for later. More females will eagerly fill their mouths with eggs and males will have more mates. This is also more conducive to the maintenance of the species.'

However, according to Tony Wilson, an evolutionary biologist at Brooklyn College, this is only a small-scale study, so it is still too early to draw any conclusions. Scientists need to study more deeply and refer to more data to come to the most accurate conclusions.