The guppy (Poecilia reticulata) is one of the world’s most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. Guppies originate from northeast South America, but have been introduced to many environments and are now found all over the world. They are highly adaptable and thrive in many different environmental and ecological conditions. Male guppies, which are smaller than females, have ornamental caudal and dorsal fins.