Spanish biologist Ignacio Paulin became fascinated by the behavior of these fish, in a project that could now disappear due to budget cuts by the Trump administration ...

Guppies can be fooled by optical illusions into believing objects are smaller or larger than they really are. This suggests they might not always make the best choices in their natural environment.

Guppies are a small, pretty species of fish that are extremely popular for home aquariums. While they’re fun in captivity, in the wild they can cause major trouble. Native to South America, guppies ...

Duping a guppy is easier than duping a ring dove — at least when it comes to a classic optical illusion. In the Ebbinghaus illusion, two identical circles placed side by side are each framed by a set ...

A 1976 experiment with Trinidadian guppies revealed evolution's rapid pace. When moved from predator-rich streams to calmer ...

Young guppies who were able to see and interact with live fish developed larger brains than guppies who only saw other fish on a screen. This is shown in a new study from Stockholm University, ...