Opah

An opah is a large, round-bodied marine fish in the genus Lampris. It is notable for retaining heat throughout much of its body, an unusual form of warm-bloodedness among fishes.

Countercurrent exchange: A heat or substance transfer process in which adjacent flows move in opposite directions. Blood vessels in the opah’s gills exchange heat in this arrangement, limiting heat loss to seawater.
Lampris: A genus of large, deep-bodied marine fishes commonly called opahs. Opah names the fishes in this genus, whose species share the characteristic rounded form.
Commercial fishing: The capture of aquatic organisms for sale and large-scale human use. Opahs are caught and marketed as seafood, including by longline fisheries.
Swordfish: A large predatory billfish with a long, flattened bill and a tall dorsal fin. Like opahs, swordfish occupy open-ocean habitats and can regulate heat in some tissues.
Endothermy: The physiological production and retention of metabolic heat to keep body tissues warmer than the surroundings. The opah’s warm body is a distinctive case of endothermy in a fish.
Teleost: A diverse group of bony fishes with highly mobile jaws and a skeleton that is partly ossified. The opah belongs to this broad and species-rich group of fishes.
Longline fishing: A fishing method using a main line bearing many baited hooks on branch lines. This gear can catch opahs alongside target species such as tuna and swordfish.
Tuna: A group of fast-swimming marine fishes in the tribe Thunnini. Tunas are another active pelagic fish lineage with specialized heat-retaining circulation.
Fish gill: A respiratory organ that extracts dissolved oxygen from water as it passes over thin exchange surfaces. The gills both take up oxygen and host the vessel network that helps conserve the opah’s heat.
Pelagic fish: A fish that lives in the open water column rather than on the seafloor or shoreline. Opahs inhabit open-ocean waters rather than a fixed reef or bottom habitat.

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