Smelts, Galaxiids, and Relatives: Osmeriformes

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AYU (Plecoglossus altivelis): SPECIES ACCOUNTS


Smelts, galaxiids, and their relatives are pointed at the ends. Smelts are silvery. Galaxiids and the relatives have a silvery belly but otherwise are brownish or olive with stripes or spots of various colors. These fishes are 1 to 28 inches (2.5 to 71 centimeters) long. Some have very large eyes, and some have no teeth in the upper jaw. Most galaxiids are scaleless.


Smelts, galaxiids, and their relatives live all over the world except near the equator and in Antarctica.


Smelts, galaxiids, and their relatives live in raging mountain streams, slow-flowing rivers, ponds, lakes, estuaries (EHS-chew-air-eez), or where a river meets the sea, shallow nearshore areas of the ocean, and the deep sea, where some live in open water and others on the bottom.


Smelts, galaxiids, and their relatives eat bottom-dwelling or open-water insects; crustaceans (krus-TAY-shuns), or water-dwelling animals that have jointed legs and a hard shell but no backbone; fishes; mollusks (MAH-lusks), or animals with a soft, unsegmented body usually covered by a hard shell; and worms. One species feeds on the stinging cells and tentacles of jellyfishes.


Scientists do not know much about the behavior of smelts, galaxiids, and their relatives. They do know that some of these fishes migrate (MY-grayt) or move to another area to spawn and that others migrate at different stages of life. During upstream migrations, some of these fishes "climb" obstacles as high as 33 feet (10 meters) by jumping and wriggling in an eel-like manner, using their fins to lever themselves forward and upward. Two behavior patterns are likely in some deep-sea smelts, galaxiids, and relatives. First, those that live in the middle depths move to the surface at night to feed on animal plankton, or microscopic animals drifting in bodies of water. Second, some of these fishes have glowing organs thought to be used for attracting mates, attracting prey or food animals, and hiding from predators (PREH-duh-terz) or animals that might hunt and eat them.

Reproductive behavior varies greatly among smelts, galaxiids, and their relatives. Some undertake long migrations (my-GRAY-shunz) from coastal seas to surf beaches and estuaries. When they reach their destination, the fish often form massive spawning groups. The males press against females until they release their eggs. The males then release their sperm. Wave action buries the fertilized eggs below the sand. Other species move up into rivers and lakes to spawn.


Smelts, galaxiids, and their relatives are used for commercial and recreational fishing.


The World Conservation Union (IUCN) lists one species of smelts, galaxiids, and their relatives as Extinct, four as Critically Endangered, one as Endangered, nine as Vulnerable, and five as Lower Risk/Near Threatened. Extinct means no longer in existence. Critically Endangered means facing extremely high risk of extinction in the wild in the near future. Endangered means facing very high risk of extinction in the wild in the near future. Vulnerable means facing high risk of extinction in the wild. Low Risk/Near Threatened means at risk of becoming threatened with extinction in the future. The U.S. Fish and Wildlife Services lists one species as Threatened, or likely to become endangered in the near future.

AYU (Plecoglossus altivelis): SPECIES ACCOUNTS

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.

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. ∎


Physical characteristics: Australian smelt are about 4 inches (10 centimeters) long. The dorsal fin that runs along the top of the body is toward the rear of the fish, and an adipose fin is present. There are no scales on the head. These fish are olive green on the back, golden to orange or purple on the sides, and silvery on the belly. Australian smelt often smell like cucumbers when fresh.

Geographic range: Australian smelt live in southeastern Australia.

Habitat: Australian smelt live in slow-flowing streams and rivers, lakes and ponds, and pools. They also live in waters with a low salt content. In open water these fish live at all depths.

Diet: Australian smelt eat insects, microscopic crustaceans, and algae.

Behavior and reproduction: Australian smelt form large schools from middle depths to the surface in large open bodies of water. They spawn in freshwater in the spring. Spawning fish develop bumps on their scales and fin rays. They release one hundred to one thousand sticky eggs over water plants in the stream bed. The eggs hatch after ten days.

Australian smelt and people: Australian smelt were introduced to Tasmania as forage or hunted food for introduced trouts.

Conservation status: Australian smelt are not threatened or endangered. ∎



Berra, Tim M. Freshwater Fish Distribution. San Diego, CA: Academic Press, 2001.

Web sites:

"Australian smelt Retropinna semoni." Basin Kids. (accessed on September 26, 2004).

"Ayu Fishing." Yamasa Institute. (accessed on September 26, 2004).

"Osmeriformes." All Science Fair Projects. (accessed on September 26, 2004).