Tiny guppy fish change their eye colour to warn off rivals, new research shows. When facing an opponent, Trinidadian guppies rapidly turn their irises from silver to black before attacking their ...

The way guppy fish behave suggests they can be tricked into believing holes are larger or smaller than they really are – but they don’t always interpret the optical illusions in the same way ...

The more colorful males were up to two times more sexually active than other guppies. Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent every weekday.

Carwile had five tanks of guppies as a kid, and he wanted to breed the fish for competition even then. "That idea was latent for a long time," Carwile remembers.

Tiny guppy fish change their eye colour to warn off rivals, new research shows. When facing an opponent, Trinidadian guppies rapidly turn their irises from silver to black before attacking their ...