Stickleback, the common name for a family of small fish native to the Northern Hemisphere. The name comes from the two or more sharp spines that are found on the back. There are about a dozen species, found in fresh and salt water. Some species can survive in either fresh or salt water. Sticklebacks range from one to seven inches (2.5 to 18 cm) in length and are generally mottled brownish in color. They have no scales, but some have a series of bony plates covering their sides.

At mating time, the male builds a tubelike nest of vegetation glued together with a secretion from his kidneys. He then lures the female into the nest, where she lays her eggs. After fertilizing the eggs, the male guards the nest and cares for the young. Sticklebacks are popular aquarium fishes. They are usually not kept together with other kinds of fish because they are aggressive.

Sticklebacks make up the family Gasterosteidae.