This Fish Hijacks Females Eggs And Clones Itself


Tom Hale

Senior Journalist

clockMay 29 2017, 13:01 UTC

The weird and wonderful Squalius alburnoides. David Perez/Wikimedia Commons (CC BY 3.0)

Don’t be tricked by its unremarkable appearance, the Squalius alburnoides is a very strange fish indeed, especially with regards to its self-cloning and egg-stealing sex life.


Scientists from the University of Lisbon have discovered that the male of the species is able to clone itself through a mysterious process known as androgenesis. Although researchers have documented this form of sexual parasitism before, their work is the first evidence of naturally occurring androgenesis in vertebrates. Their study into this endangered self-replicating mastermind was recently published in the journal Royal Society Open Science.

The researchers sampled 261 randomly selected S. alburnoides from the Ocreza river in central Portugal only to discover, much to their surprise, that one of the fish was genetically identical to another one and had only paternal chromosomes. However, they found that this individual did not share the mitochondrial DNA with his father, as they can only obtain this from their mother’s egg.

It’s unclear how frequently this phenomenon occurs among the species. In fact, there’s a chance it could just be a freak occurrence. Nevertheless, this one occurrence remains “the first report of naturally occurring spontaneous androgenesis among vertebrates,” the authors write. Previously it’s only been seen in arthropods and mollusks.

Here’s how they think it might work. Androgenesis is a way of reproduction where all the genetic material of the offspring comes from the male. In terms of this fish, the male produces sperm with twice the amount of genetic content as usual. They will then hijack a female egg that (for some reason) doesn’t contain any genetic material. Perhaps the males destroy the egg’s genetic material somehow or perhaps the egg “accidentally” just doesn't contain chromosomes, the researchers admit they really aren't sure yet.


S. alburnoides, typically no longer than around 15 centimeters (5.9 inches), can be found swimming in the rivers of Portugal and Spain. To add to the bizarreness of this little beast, it’s actually a hybrid species of two separate fish species, one of which is now believed to be extinct. This could help explain how the fish came to be capable of such a bizarre method of asexually reproducing.

“In a lot of these cases,” evolutionary biologist Laura Ross, who was not involved in the study, told the Scientist, “these bizarre types of reproduction seem to have arisen by two closely related species hybridizing at some point in their evolutionary history and something going really, really wrong with reproduction.”

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