CUSK-EELS AND RELATIVES: Ophidiiformes

PHYSICAL CHARACTERISTICS

Most cusk-eels and their relatives are long and thin. The dorsal (DOOR-suhl) and anal (AY-nuhl) fins are very long, reaching the tail fin in some species. The dorsal fin is the fin along the midline of the back. The anal fin is the fin along the midline of the belly. The tail fin of these fishes is small, sometimes just a bony point. Cusk-eels and their relatives are about 1½ inches (4 centimeters) to 6 feet, 6 inches (2 meters) long. Some species have long, thick barbels (BAR-buhls) on the chin. Barbels are feelers used for the senses of taste, touch, and smell. Cusk-eels often have black or brown markings or bands extending the length of the body. Some relatives are covered with small spots, and others are colorless. Some species have long pectoral (PECK-ter-uhl) fins, which are the front pair and correspond to the front legs of four-footed animals. Scales can be absent, but when present, they generally are small. The pelvic fins are either very small or absent. The pelvic fins are the rear pair and correspond to the rear legs of four-footed animals.

GEOGRAPHIC RANGE

Cusk-eels and their relatives live all over the world.

HABITAT

Cusk-eels and their relatives live in the ocean, some in very deep water and some in shallow seas and estuaries (EHS-chew-air-eez), or the areas where rivers meet the sea. Most of these fishes are bottom dwellers that live in mucus-lined mud or sand burrows, rock or coral crevices, or sea caves. Some live with communities of bottom-dwelling invertebrates (in-VER-teh-brehts), or animals without backbones, such as tube worms. Some species live in the body cavity of invertebrate hosts, such as pearl oysters, giant clams, and sea cucumbers. Some species live in freshwater caves.

DIET

Most cusk-eels and their relatives look for bottom-dwelling animals during evening hours. They eat invertebrates and small bottom fishes.

BEHAVIOR AND REPRODUCTION

Many cusk-eels and their relatives produce sound with their swim bladder, forward vertebrae (ver-teh-BREE), and the ligaments and muscles attached to those vertebrae. The swim bladder is an internal sac that fishes use to control their position in the water. Vertebrae are the bones that make up the spinal column. In some cuskeels and their relatives, the swim bladder is hard and serves as an echo chamber. Some species make the sound just before mating.

Cusk-eels and their relatives usually hide in burrows or crevices or in or around invertebrate hosts during daylight hours and then exit at night to look for food. Some never leave the host and constantly feed on its internal organs.

Cusk-eels and their relatives either release eggs or bear live young. Eggs are released in open water and float individually or are deposited in a gummy raft. The egg rafts float at the ocean surface until they hatch, usually within several days. Larvae (LAR-vee) of some species float near the surface and sometimes travel great distances from their hatching place. Larvae are animals in an early stage and must change form before becoming adults.

HOME SWEET CUCUMBER

The pearlfish uses its snout to locate the anus of the sea cucumber. Holding its head in the anus, the pearlfish curves its body and tracks the tip of its tail along the sea cucumber until the tail reaches the cucumber's anus. Once it has the tip of its tail aligned and pointed into the anus, the pearlfish turns abruptly and forces its way tail first into the sea cucumber.

CUSK-EELS, THEIR RELATIVES, AND PEOPLE

Cusk-eels are large; their meat is tasty, and they are fished commercially.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists seven species of cusk-eels and their relatives as Vulnerable, or facing high risk of extinction in the wild.

PEARLFISH (Carapus bermudensis): SPECIES ACCOUNT

Physical characteristics: Pearlfish are long, slender, and eel-like. The skin is cloudy, almost clear, with silvery bands along the sides and black along the back. The cheeks are silver, and there are blotches of color at the bases of the dorsal and anal fins and on the head. The dorsal and anal fins extend almost the length of the body. There are no pelvic fins and usually no tail fin. The teeth on the upper jaw are small, and some are heart-shaped. The teeth on the lower jaw are larger and cone shaped. The swim bladder is separated into two parts.

Geographic range: Pearlfish live in the western Atlantic Ocean from Bermuda to Brazil.

Habitat: Pearlfish live in sea cucumbers, which usually live in shallow waters to about 98 feet (30 meters) on sandy bottoms or grass beds in warm lagoons near reefs.

Diet: Pearlfish eat crustaceans (krus-TAY-shuns), or water-dwelling animals that have jointed legs and a hard shell but no backbone, such as small shrimps and crabs.

Behavior and reproduction: Pearlfish live in the bodies of sea cucumbers during the day and exit at night to look for food and perhaps to spawn, or release eggs. Pearlfish deposit their eggs into a jellylike blob that floats at the surface. Eggs hatch in one to two days. Pearlfish larvae are remarkable in that they undergo two separate growth phases. In the first phase the larvae have a long, showy thread in front of the dorsal fin. These larvae are very long, about 7 inches (18 centimeters). In the second phase the larvae shrink to about half their original length.

Pearlfish and people: Pearlfish are rarely seen and are not fished commercially.

Conservation status: Pearlfish are not threatened or endangered. ∎

FOR MORE INFORMATION

Books:

FAO Species Catalogue: Ophidiiform Fishes of the World. Rome, Italy: Food and Agriculture Organization of the United Nations, 1999.

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

Web sites:

"The Cusk Eel Is All Talk, Some Slime." Points East.http://www.pointseast.com/thegulf/040701eel-ad.shtml (accessed on October 6, 2004).

"Cusk eel Lepophidium cervinum (Goode and Bean) 1885." Fishes of the Gulf of Maine. http://www.gma.org/fogm/Default.htm (accessed on October 6, 2004).