TOADFISHES: Batrachoidiformes

OYSTER TOADFISH (Opsanus tau): SPECIES ACCOUNT

PHYSICAL CHARACTERISTICS

Toadfishes have a broad, flat head and a wide mouth, which usually has thick barbels or flaps of skin around it. Barbels (BAR-buhls) are feelers used for the senses of taste, touch, and smell. The eyes are on the top of the head and face upward. Some toadfishes have light organs along their sides and belly. Other toadfishes have hollow, venomous spines in the first dorsal (DOOR-suhl) fin and gill cover. The dorsal fin is the one along the midline of the back.

The fin arrangement of toadfishes is unusual in that the pelvic fins, which correspond to the hind legs of four-footed animals, are forward of the pectoral (PECK-ter-uhl) fins, which correspond to the forelegs of four-footed animals. The pectoral fins of toadfishes are large. There are two separate dorsal fins. The first is small and has two or three spines, and the second is long, almost the length of the body. The anal (AY-nuhl) fin is a bit shorter than the second dorsal fin. The anal fin is the one on the midline of the belly.

Toadfishes are small to medium sized, about 2 to 20 inches (5 to 51 centimeters) long. They are usually rather drab, often brownish with darker saddles, bars, or spots. Some, however, are brightly colored.

GEOGRAPHIC RANGE

Toadfishes live all over the world.

HABITAT

Toadfishes live in saltwater from shoreline waters with a low salt content down to deep sea water, about 1,200 feet (366 meters). These fishes sometimes enter rivers. Their camouflage allows toadfishes to blend with the bottom, where they bury themselves and ambush their prey, or animals caught for food. One species lives in the sand under coral heads.

DIET

In addition to ambushing their prey, toadfishes move about feeding on invertebrates, or animals without backbones, such as crabs, shrimps, mollusks (MAH-lusks), and sea urchins. Some eat fish, and some eat plankton. Mollusks are animals with a soft, unsegmented body usually covered by a hard shell, such as snails and clams. Plankton are microscopic plants and animals drifting in water.

BEHAVIOR AND REPRODUCTION

Toadfishes produce sound by contracting muscles on their swim bladder, which is an internal sac that fishes use to control their position in the water. Both males and females produce grunts, but only males make longer courtship calls, which sound like boat whistles or humming.

Male toadfishes prepare nests, usually under rocks or shells but sometimes under objects discarded by humans, such as cans and bottles. Males attract females by making their sounds, and then females lay large, sticky eggs and leave the area. Males guard and fan the eggs until after hatching. Fanning is using the fins to move water over the eggs to clean them and make sure they have plenty of oxygen. The young may remain in the nest after hatching. One species of toadfish has two types of males, larger nest-holding ones and smaller sneaker males that dart into nests attempting to fertilize (FUR-teh-lyze), or place sperm on, eggs of a nesting pair.

THE RIGHT STUFF: THE SENATOR AND THE TOADFISH

Two oyster toadfish accompanied the former senator John Glenn and several other astronauts on space shuttle mission STS-95 in October 1998. Glenn, one of the original Mercury astronauts in the 1960s, was the first American to orbit Earth.

A Helpful Fish

Oyster toadfish are used in studies of hearing, dizziness, and motion sickness, of insulin and diabetes, and of the effects of drugs.

TOADFISHES AND PEOPLE

Large toadfishes are eaten. One species is collected and sold in the aquarium business. Another species is used in laboratory studies. Venomous toadfishes can inflict pain if handled.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists five species of toadfishes as Vulnerable, or facing high risk of extinction in the wild.

OYSTER TOADFISH (Opsanus tau): SPECIES ACCOUNT

Physical characteristics: Oyster toadfish grow as long as 15 inches (38 centimeters). They have three dorsal-fin spines, no scales, and a spine under the gill cover. The second dorsal fin has 23 to 27 soft rays, and the anal fin has 19 to 23 soft rays. The body is dark and has no spots. The pectoral fin has cross bars.

Geographic range: Oyster toadfish live along the Atlantic coast of the United States.

Habitat: Oyster toadfish usually live over rock, sand, mud, or oyster shell bottoms in estuaries (EHS-chew-air-eez), areas where a river meets the sea.

Diet: Oyster toadfish feed mainly on small crabs and other crustaceans (krus-TAY-shuns), which are water-dwelling animals that have jointed legs and a hard shell but no backbone.

Behavior and reproduction: Oyster toadfish make a grunting noise by rubbing muscles across their swim bladder. Males use a boat-whistle call to attract females to nesting sites. Males establish nesting sites from April through October.

Oyster toadfish and people: Oyster toadfish are helpful to people because they are used for medical studies.

Conservation status: Oyster toadfish are not threatened or endangered. ∎

FOR MORE INFORMATION

Books:

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

Niesen, Thomas M. The Marine Biology Coloring Book. 2nd ed. New York: HarperResource, 2000.

Web sites:

"Toadfish." All Science Fair Projects. http://www.all-science-fair-projects.com/science_fair_projects_encyclopedia/Toadfish (accessed on October 8, 2004).

"Toadfish Song May Help Heal Humans." CNN.com. http://www.cnn.com/2003/TECH/science/12/19/toadfish.song.ap (accessed on October 8, 2004).

"Toadfish in Space." Marine Biological Laboratory. http://www.mbl.edu/publications/LABNOTES/8.2/toadfish.html (accessed on October 8, 2004).