Swiss scientists have discovered that male sticklebacks ejaculate more sperm if first stimulated by a "soft porn" film featuring "virtual" flirting fish.
The University of Fribourg researchers believe the fish porn simulates conditions in the wild where mating male sticklebacks ejaculate more if they are threatened by other finned Romeos swimming nearby.
Stickleback mating is a cut-throat business. The male builds a nest, starts elaborately courting a female and she, when she is charmed enough, lays eggs in his nest for him to ejaculate over and fertilise.
But often other males try to fertilise the eggs as well.
Males who feel their nest is threatened ejaculate more to raise their chances of being the first to father the baby fish.
A report in New Scientist said the researchers showed 17 male sticklebacks (in separate tanks) two films using computer-animated fish: one a "sexy" courting film; the other of a male caring for his brood.
After each stickleback had watched one film for a couple of minutes, a female was put in the tank to spawn. Each fish ejaculated more sperm over the eggs if they had seen the fish "porn" film.