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.

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 ...

When Robert Heathcote dips his head into the rivers of Trinidad, he’ll often see little black dots moving through the water, even when it’s murky. Those dots are the eyes of small, inch-long fish ...