Guppy

The guppy is a small livebearing fish in the family Poeciliidae, native to freshwater streams of Trinidad, Venezuela, Guyana, and nearby parts of northeastern South America. It has since been introduced to warm-water habitats on nearly every continent, both intentionally for mosquito-larvae control and through the aquarium trade. Guppies are among the most widely kept aquarium fish in the world and have been selectively bred into an enormous range of tail shapes and color patterns known as 'fancy guppies.' As a livebearer, the species does not lay eggs but gives birth to free-swimming young, a trait shared with mollies, platies, and swordtails within the same family.

Guppies show strong sexual dimorphism, making males and females easy to tell apart.

• Males: 2-3.5 cm, slender body, large ornate caudal (and often dorsal) fin in spots, stripes, marbling, or solid colors
• Females: 4-6 cm, larger and rounder body, mostly plain gray-olive with a dark 'gravid spot' near the anal fin when pregnant
• Mouth: small and upturned, adapted for surface feeding
• Tail shapes (selectively bred): fan, delta, veil, lyretail, and others

Wild-type guppies are duller than the brightly colored fancy strains sold in the aquarium trade.

Guppies naturally inhabit shallow, warm freshwater streams, ditches, and ponds in Trinidad and adjacent regions of northeastern South America, often in slow-flowing water with dense vegetation. They tolerate a wide range of water conditions, including brief exposure to brackish water, and thrive at temperatures between about 22-28°C. Because of their hardiness and tolerance for poor water quality, guppies have established wild or feral populations in warm regions worldwide, including parts of Africa, Asia, Australia, and the southern United States, typically in slow streams, canals, and ponds. In the aquarium hobby they are kept in still or gently filtered freshwater tanks with plants for cover.

Guppies are a livebearing species, meaning females retain fertilized eggs internally and give birth to fully formed, free-swimming fry rather than scattering eggs. Breeding is continuous under suitable conditions, with females capable of storing sperm and producing multiple broods from a single mating. Males display near-constant courtship behavior, flaring their fins and performing sigmoid displays to attract females, and the species has a highly polygamous mating system. Guppies are social, forming loose shoals in open water, and are active during the day, grazing on algae, small invertebrates, and detritus, as well as mosquito larvae in the wild, which has made them useful for natural mosquito control programs.