RAINBOWFISHES AND SILVERSIDES: Atheriniformes

PHYSICAL CHARACTERISTICS

Silversides are long and narrow from side to side. They have two dorsal (DOOR-suhl) fins, a single anal (AY-nuhl) fin spine, usually smooth scales, and no lateral line. Most are silvery and have a stripe along each side of the body. Male rainbowfishes are brilliantly colored with patterns in shades of red, yellow, orange, blue, and green. The anal and dorsal fins sometimes have threadlike extensions or elaborate fanlike shapes. The anal fin is the one along the midline of the belly. The dorsal fin is the one along the midline of the back. A lateral line is a series of pores and tiny tubes along each side of the body, used for sensing vibrations.

GEOGRAPHIC RANGE

Rainbowfishes and silversides live all over the world.

HABITAT

Rainbowfishes and silversides live in coastal areas of seas; estuaries (EHS-chew-air-eez), areas where rivers meet the sea; reefs; lagoons, and the surf along beaches. Only a few species live in the open water. Freshwater species live in lakes and streams, rain-forest pools, spring-fed desert waterholes, and mountain lakes.

DIET

Rainbowfishes and silversides eat invertebrates, which are animals without backbones; algae; and plankton. Some species eat fish larvae. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves. Plankton are microscopic plants and animals drifting in the water. Larvae (LAR-vee) are animals in an early stage that must change form before becoming adults.

BEHAVIOR AND REPRODUCTION

Rainbowfishes and silversides form schools of various sizes. Some saltwater silversides form schools numbering in the thousands and cruise just below the surface, constantly feeding on plankton. Some schools are more than 328 feet (100 meters) long and 66 feet (20 meters) wide. At night silversides are attracted to bright lights and are caught easily by fishermen for use as bait.

Rainbowfishes and silversides are known for their unusual reproductive behaviors. These fishes have large eggs with sticky filaments that are used to anchor the eggs to plants or other materials at the bottom of the water. Female rainbowfishes spawn, or release eggs, day after day for a long time. The eggs attach themselves by a thread to underwater plants. Grunions time their spawning to take advantage of the tides.

RAINBOWFISHES, SILVERSIDES, AND PEOPLE

Most rainbowfishes and silversides are not eaten by humans. Saltwater silversides are important to commercial fishing because they are an important food source for fishes that people do eat. Silversides that are fished are used as bait or are converted into pet food. Because of their extraordinary colors, rainbowfishes are valued in the aquarium business. Most of the rainbowfishes sold in pet stores are bred in captivity, but some have been fished heavily to satisfy the demands of aquarium owners.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists one species of rainbowfishes and silversides as Extinct, six species as Critically Endangered, five as Endangered, thirty-one as Vulnerable, and eight as Near Threatened. Extinct means no longer in existence. Critically Endangered means facing an extremely high risk of extinction in the wild. Endangered means facing a very high risk of extinction in the wild. Vulnerable means facing a high risk of extinction in the wild. Near Threatened means at risk of becoming threatened with extinction in the near future. The U. S. Fish and Wildlife Service lists one species as Threatened, or likely to become endangered in the near future.

CALIFORNIA GRUNION (Leuresthes tenuis): SPECIES ACCOUNT

Physical characteristics: California grunion grow to 7½ inches (19 centimeters). They are long silversides with a prominent silvery band on the sides and bluish green on the back.

Geographic range: Grunion live on the coast of North America from Monterey Bay, California, in the United States to the southern part of the Baja Peninsula in Mexico.

Habitat: California grunion live in coastal ocean waters.

Diet: California grunion eat animal plankton.

Behavior and reproduction: California grunion are known for their spawning behavior. They emerge from the surf in large groups to spawn on beaches during the highest tides of the spring and summer months. Both males and females ride in on waves and are left exposed on the sand when the water recedes. Females burrow tail first into the sand to deposit their eggs, and males place sperm on the eggs as they are released. The eggs are left buried in the sand a few inches below the surface and hatch in about two weeks, when they are agitated by another high tide. After spawning, adults return to the sea. They can spawn numerous times.

California grunion and people: California grunion are collected by hand during spawning runs.

Conservation status: California grunion are not threatened or endangered. ∎

FOR MORE INFORMATION

Books:

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

Gilbert, Carter Rowell, and James D. Williams. National Audubon Society Field Guide to Fishes: North America. New York: Knopf, 2002.

Schultz, Ken. Ken Schultz's Field Guide to Saltwater Fish. New York: Wiley, 2004.

Web sites:

"The Amazing Grunion." California Department of Fish and Game, Marine Region. http://www.dfg.ca.gov/mrd/grnindx3.html (accessed on October 11, 2004).

"The California Grunion." Dr. C's Remarkable Ocean World. http://www.oceansonline.com/index.htm (accessed on October 11, 2004).