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Any of about 12 species (family Gasterosteidae) of slender, scaleless fishes inhabiting temperate fresh and salt waters of the Northern Hemisphere. Sticklebacks grow to 6 in. (15 cm) long. They have a row of spines on the back, in front of a soft-rayed dorsal fin, and a sharp spine in each of the pelvic fins. They also have a slender tail base, a squared tail, and hard armour plates on their sides. The male builds a nest of plant materials and coaxes one or more females into it to lay eggs, fertilizes the eggs in the nest, and aggressively defends eggs and young.
This entry comes from Encyclopædia Britannica Concise. For the full entry on stickleback, visit Britannica.com.