Galaxiids Smelts and Relatives: Osmeriformes

Physical characteristics: Ayu are about 12 inches (30 centimeters) long. The body is covered in small scales. The dorsal (DOOR-suhl) fin is midway between the head and the tail. These fish have an adipose (AE-dih-POS) fin that sits between the end of the dorsal fin and the start of the tail. Ayu are olive on the back and sides and white on the belly.

Geographic range: Ayu live in coastal seas and rivers in Japan, China, Korea, and Taiwan.

Habitat: Ayu live in both saltwater and freshwater. At different stages of life they live at the bottom of coastal seas, estuaries, rivers, streams, and lakes.

Diet: Ayu larvae (LAR-vee) and young mainly eat small bottom-dwelling crustaceans. Adults use their jaws and teeth to scrape algae (AL-jee), or tiny plantlike growths that live in water and have no true roots, stems, or leaves, from rocks.

Ayu live in both saltwater and freshwater. At different stages of life they live at the bottom of coastal seas, estuaries, rivers, streams, and lakes. (Illustration by Jonathan Higgins. Reproduced by permission.)

Behavior and reproduction: In rivers ayu form territories, which they guard by attacking and nipping other ayu. Ayu spawn in freshwater in the autumn, when adults move downstream to the spawning grounds. At night, the fish dig small pits in sand or gravel banks into which the female releases about ten thousand sticky eggs. The eggs hatch about two weeks later. Larger ayu spawn once and die. Smaller ones have about a 50 percent chance of surviving to spawn again two weeks later.

Ayu and people: Ayu are caught for food, raised for food, and caught for fun.

Conservation status: Ayu are not threatened or endangered. ∎