The guppy (Poecilia reticulata), also known as the millionfish or rainbow fish,[3] is a member of the family Poeciliidae and, akin to most New World members of the family, is considered a livebearer.[4] Male guppies, which are smaller than females, have ornamental caudal and dorsal fins. Wild guppies generally feed on a variety of food sources, including benthic algae and the larvae of aquatic insects.[5]

Originating from northeast South America, it has been introduced to many environments and are now found all over the world; guppies are now one of the world's most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. They are highly adaptable and thrive in many different environmental and ecological conditions.[6] Guppies are used as a model organism in the fields of ecology, evolution, and behavioural studies.[6]