Family: Gasterosteidae, Sticklebacks view all from this family

Description To 4" (10 cm). Fusiform; gray to olive-brown, sides paler, belly silvery; breeding adults reddish on head and belly. Head one-fourth length; lower jaw projects beyond upper. Usually 3 stout, widely separated dorsal spines preceding soft dorsal fin. Caudal peduncle narrow; caudal fin triangular. Sides covered with series of bony plates.

Endangered Status The Unarmored Threespine Stickleback, a subspecies of the Threespine Stickleback, is on the U.S. Endangered Species List. It is classified as endangered in California. The primary causes of this species' decline are the introduction of exotic fishes, which prey on it and compete with it for food; destruction or degradation of its habitat by urban development and water-management practices; and its intergrading with other subspecies of sticklebacks.

Related Species Fourspine Stickleback (Apeltes quadracus) has 4 dorsal spines; no bony plates; occurs in similar habitat, less frequently in fresh water, from Gulf of St. Lawrence to Virginia. Blackspotted Stickleback (G. wheatlandi) has black spots, 2 soft pelvic fin rays, 3 weaker dorsal spines, and no bony plates; occurs in salt water south from Newfoundland to s. Massachusetts.

Habitat Marine, estuarine, and fresh water, usually in vegetation.

Range In Atlantic, from Hudson Bay to Chesapeake Bay; in Pacific, from Bering Sea to N. Baja California and in associated freshwater streams.

Discussion These shore fishes enter brackish water or ascend freshwater streams to spawn from April to July. The female deposits 75-100 eggs on a nest built by the male, which guards the eggs and remains with the fry until they can fend for themselves.