Some fish are able to get sex by faking out the females. Now scientists have found a gene that helps them do so.

The fish, known as cichlids, are maternal mouthbrooders???the female scoops up eggs in her mouth after she lays them. While collecting her eggs, the female may mistake the yellow, oval-shaped markings on a male’s fin as one of her own eggs and approaches the male. Once she gets close enough to his anal fin, he then squirts sperm into her egg-filled mouth.

This form of mating ‘trickery’ works so well that more than 80 percent of cichlid species evolved the fake egg markings.

Researchers at the University of Germany identified the gene associated with the egg-like markings by observing how the gene was expressed in distantly related species, where such spots developed on the pectoral fins rather than the anal fins.

The researchers published their findings in the online open access journal BMC Biology.

"The two kinds of independently evolved egg-dummies serve as a model system to test whether the same genetic pathways are involved in the morphogenesis of both types of dummies," the authors write.