OPAHS AND RELATIVES: Lampridiformes

PHYSICAL CHARACTERISTICS

Opahs are almost round when viewed from the side, but their relatives are long and slender. Opahs and their relatives have red fins and brightly colored bodies. The jaw structure allows these fishes suddenly to open their mouths to forty times the closed size and use enormous suction to capture plankton, or microscopic plants and animals drifting in water.

GEOGRAPHIC RANGE

Opahs and their relatives live in all oceans except in polar waters.

HABITAT

Opahs and their relatives are strictly saltwater fishes. Some live near the shore, and some live in the deep ocean, from surface waters to depths of hundreds of feet.

DIET

Opahs and their relatives eat crustacean (krus-TAY-shun) plankton, small to medium-sized squid, and small to medium-sized fishes. Crustaceans are water-dwelling animals that have jointed legs and a hard shell but no backbone.

BEHAVIOR AND REPRODUCTION

Scientists do not know much about opahs and their relatives. The long forms hold themselves straight up and down in the water. The other forms swim belly down and head forward the way most fish do. Opahs are powerful swimmers, using their large pectoral (PECK-ter-uhl) fins to move themselves forward. The pectoral fins are the front pair, corresponding to the front legs of four-footed animals. One opah relative delivers a mild electric shock when handled. Other species release ink when disturbed.

Opahs and their relatives probably scatter their eggs. The eggs are large and brightly colored, usually red, pink, or amber. Fertilized (FUR-teh-lyzed) eggs, or those that have been penetrated by sperm, develop in surface waters for approximately three weeks. At hatching, larvae (LAR-vee), or the early stage that must change form before becoming an adult, have fully developed mouths and digestive tracts, are able to take in food, and begin immediately to feed on plankton.

OPAHS, THEIR RELATIVES, AND PEOPLE

Opahs and their relatives, especially the large, long species, attract considerable public attention when they are stranded or beached, because of their rarity and unusual appearance. Opahs have excellent meat and are prized when they are caught by commercial fishermen going for other fish. The relatives are considered inedible by those who have tasted them.

SEA SERPENT

The oarfish is a fabled species whose tremendous length, bright crimson fins, long dorsal rays, silvery form, and tendency to appear suddenly at the ocean surface after wind storms brought fearful cries of "sea monster!" from sailors 100 years ago.

CONSERVATION STATUS

Opahs and their relatives are not threatened or endangered.

OARFISH (Regalecus glesne): SPECIES ACCOUNT

Physical characteristics: Oarfish are spectacular animals with long, slender, usually silver bodies, brilliant red fins, a large plume of dorsal fin rays on the head, and long pelvic or back fins. Often attaining a length of 26–33 feet (8–10 meters), oarfish are the longest of all bony fishes. The pelvic fin ray has a large red swelling at its tip that looks like the blade of an oar. The tail fin is tiny, but it has very long rays that are covered in small spines. Oarfish have about four hundred dorsal (DOOR-suhl) fin rays and 150 vertebrae (ver-teh-BREE), which are the small bones that make up the spinal column. The dorsal fin is the fin along the midline of the back. The pelvic fins are the rear pair, corresponding to the rear legs of four-footed animals. Rays are the supporting rods in fins.

Geographic range: Oarfish live in all oceans, including the Mediterranean Sea, but not in polar seas.

Habitat: Oarfish live in open water near the surface to depths of about 656 feet (200 meters).

Diet: Oarfish eat crustacean plankton and small fishes.

Behavior and reproduction: Oarfish move by wavy movement of the dorsal fin. The natural body position is head up with the dorsal fin rays and pelvic rays extended outward; the fish swim up and down in the water this way. The pelvic fin may allow oarfish to "taste" the surrounding habitat. Scientists know little about the reproduction of oarfish. The eggs drift in open water and have been found in plankton collections. Researchers report that eggs can take up to three weeks to hatch and that the larvae are close to their adult form at hatching.

Oarfish and people: Sightings of oarfish usually stir considerable public attention, but the species has no commercial value, and its meat is reported to be inedible.

Conservation status: Oarfish 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.

Periodicals:

Skerry, B. "Eye-to-Eye with the Sea Serpent: First Photos of the Mysterious Oarfish." Sport Diver (August 1997): 40–43.

Web sites:

"Oarfish: Regalecus glesne Ascanius, 1772." Australian Museum Fish Site. http://www.amonline.net.au/fishes/fishfacts/fish/rglesne.htm (accessed on October 4, 2004).

"Strange but True." Divernet. http://www.divernet.com/biolog/oarf198.htm (accessed on October 4, 2004).