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One of the most popular species of freshwater topical fish is the guppy. The first specimens were brought to the British Museum in London for description in 1859 by R. J. L. Guppy, a biologist from Trinidad (West Indies) after whom the fish is named. The species originally possessed the scientific name Lebistes reticulatus, but in 1963, the Latin name was changed to Poecilia reticulata and remains so today. While characteristically quite small in size, guppies display a wide range of colors and patterns, and many forms of elaborate fin and tail shapes.

The modifications in color and fins create numerous varieties of the species. The brightest and most ornate are termed fancy varieties and are highly prized as aquarium pets. Although colorful, male guppies average only 1.2 in (3 cm) in length, while the larger females average a mere 3 in (8 cm) long when mature.

Guppies belong to the phylum Chordata within the kingdom Animalia. Like many evolutionarily advanced organisms (including birds, reptiles, and mammals), guppies are vertebrates, possessing spinal cords protected by a vertebral column. Guppies also belong to the class Osteichthyes, which is the group of organisms defined as bony fish. As members of this large group, guppies have a skeleton made of bone (unlike sharks which have skeletons made of cartilage), homocercal tails (having equally sized upper and lower lobes), skin with embedded scales and mucus glands, and a swim bladder that helps control buoyancy. Guppies are also among the most evolutionarily advanced group of bony fish, known as Teleosts. Teleosts have characteristically complex, extensible mouth to aid in prey capture.

Guppies are tropical fish that prefer warm water temperatures between 73 and 83°F (22-28°C). They are a freshwater species native to Trinidad, Barbados, and Venezuela where they inhabit slow moving streams and relatively shallow lakes. In contrast to other aquatic organisms, guppies give birth to live offspring. Displaying a characteristic termed ovo-viviparity, female guppies release live immature progeny (called fry) that developed from yolky eggs within the mother rather than deriving nourishment directly from the mother herself. Captive guppies feed readily on worms, small crustaceans, small insects, and plant matter in addition to commercially available flake food. The relative ease of care and breeding of guppies, in combination with their stunning varieties, make them very popular tropical tank species.

Terry Watkins