Mouthbrooding is one of those strategies of nature that fascinate us; but not only that: it also makes a lot of sense. Many fish and amphibians, during the breeding season, lay hundreds of eggs in very vulnerable places . How to drastically reduce that risk? Incubating them inside the mouth. By housing the eggs and fry (juveniles) in the mouth, very few fish end up being preyed upon.
And who does the incubation? The male fish or the female?
There are precisely two types of mouthbrooding : maternal and paternal and this depends on the species.
Depending on the species, sometimes the mouthbrooder is the female (maternal mouthbrooding) and sometimes the male (paternal mouthbrooding). When the females incubate the eggs in their mouths, the female will lay the eggs, collect them in her mouth, and then the male will fertilize them. On the other hand, in paternal mouthbrooding species, spawning occurs before the male harbors the fertilized eggs.
The most curious thing is that biologists have discovered that some male fish act as paternal mouthbrooders when they are not even the biological parents of the eggs they are going to preserve.
For what reason?
Scientists don’t know. To impress females? Who knows.
What is certain is that previous studies have also shown that mouthbrooding affects the breeder: he cannot eat during the entire incubation time , which could be a couple of weeks until the eggs hatch. In addition, carrying a load of eggs in the mouth slows down swimming, previous research has revealed, making it easier for predators to catch them.
Delving into mouthbrooding
A team of researchers from Charles Darwin University (Australia) decided to explore the mouthbrooding process in two fish from northern Australia: the blue catfish ( Ictalurus furcatus ) and the so-called ‘almighty mouth’ (Glossamia aprion ). Both fish live in extremely muddy rivers, making it difficult to study their behavior. Fortunately, mud doesn’t hide DNA, so experts tested hundreds of members of each species to verify whether or not the eggs being cared for were the breeder’s offspring.
The biologists discovered that the eggs carried by the blue catfish were as expected: they had all been fertilized by the same male carrying them in his mouth, and all the eggs came from the same mother. However, with the other species, there was an unexpected finding: about 25% of the eggs had a different mother or had been fertilized by another male. And they even found cases in which the male carried eggs fertilized by himself but which came from more than one female.
For scientists, this finding is tremendously puzzling. They suggest that males carrying many eggs might be more attractive to females, as a male sign of offspring insurance.
Reference: Janine E. Abecia, Alison J. King, Osmar J. Luiz, David A. Crook, Dion Wedd and Sam C. Banks Diverse parentage relationships in paternal mouthbrooding fishes, Biology Letters (2022). Published:04 May 2022 DOI: 10.1098/rsbl.2021.0576
