“Virgin Mary”: the mystery of the fish that had internal fertilization!
Scientists discover the first case of the type in oviparous species.
A female snail-cat fish, dubbed “Virgin Mary” which appear to have been fertilized while still inside, according to scientists at the School of Life Sciences at the University of Nottingham in the United Kingdom.
In an article published in the journal Scientific Reports, they present the first discovery of internal fertilization and development of puppies inside an oviparous species, as well as the birth of the small fish. Of the species, Gasterosteus aculeatus is also known as thorn-billed snail-cat.
It is a small common fish in the fresh, coastal waters of the northern hemisphere.
In normal breeding, the male builds a nest and, when performing a routine zig-zag dance, draws the female to be able to lay her eggs inside her.
After attracting her, the male pursues her to fecundate her.
He guards and cares for the eggs, wagging them with their fins for about two weeks until the cubs are born. The presence of fertilized eggs in the “virgin” Mary was noted as she was almost dying.
Therefore, researchers put her to “sleep” and removed the almost complete embryos by cesarean section. In all, 54 small fish were born.
They grew into adulthood in the Nottingham aquariums, where about 20 still survive, almost three years later.
“We were impressed when we examined Mary in the laboratory. She looked like an ordinary fish with an egg, and we could not believe that she had almost completely developed embryos inside her ovaries,” said Laura Dean of the School of Life Sciences.
“This is practically unheard of in an oviparous species. The embryos were perfectly healthy, not deformed anyway, and most had a normal adult life.”
Currently, this finding is the only record of fertilization and birth of this type in fish. So the experts went to investigate how it could have happened.
There are different known reproduction mechanisms in fish. There is parthenogenesis, in which the fish clones itself.
And there is also the chance of the animal being hermaphrodite, that is, with male and female sexual organs. “We were able to rule out both possibilities because, in parthenogenesis, their offspring would have been genetically identical to the mother.
If it were hermaphroditism, they would have versions of genes that it had, without any genetic input,” Dean said. “We did some straightforward genetic tests on the offspring and found that they had versions of genes that Mary did not have, so the embryos should have a father.”
“Our theory is that sperm somehow got into it, fertilized the eggs, and became the normal embryo of two parents. What probably happened was that it was in one nest to lay their eggs where another female had already laid eggs that had been covered with sperm from a male, “she added.
“Somehow, some of the spermatozoids must have entered Mary, perhaps through her tube of eggs, and fertilized the eggs inside her, but she never even laid the eggs.”
“Although the almost accidental discovery has revealed a rare phenomenon, it may help understand a major change in the tree of life,” said Andrew MacColl, a professor of evolutionary biology.
“Most animals lay eggs, but some, almost all mammals and a few fish, keep their eggs in the body and give birth.
Although it seems difficult to achieve in evolution, this goldfish seems to have gotten there almost by itself!”
Researchers are looking for, on fishing expeditions in Scotland, for more female species that may exhibit the same phenomenon. The intention is to see if there is a chance that Mary is not just a weird incident, but an indication of a genetic or evolutionary change in the reproductive mechanism of a species.