Guppies are extremely popular aquarium fish that give birth (rather than lay eggs) and have been used for much behavioral research, including on breeding behaviors. Males have a modified anal fin, the ...

guppy males fertilise females by delivering sperm into their bodies. They don’t have a penis, as such. Instead, they have modified a fin into a penetrating organ called a gonopodium. These penis ...

Previous studies have shown that "males with a longer gonopodium had higher reproductive success". In some fish species, such as the guppy, males use two mating tactics: courtship and coercion.

The researchers examined the role of a pair of claws at the tip of the gonopodium of the male guppy (Poecilia reticulata) – essentially the fish’s penis. “Our results show that the claws are used to ...