Cusk-eels include some of the deepest-living fishes
Ophidiiformes bundles cusk-eels, pearlfishes, live-bearing brotulas, and allies among ray-finned fishes. Fossils turn up by Maastrichtian time, such as Italy’s Pastorius. Abyssobrotula galatheae came from 8,370 metres in the Puerto Rico Trench, a record depth for fish.
Members share a recognisable build: a small head on a long, slim body, skin that is either smooth-scaled or naked, and a lengthy dorsal fin, while the anal fin usually merges into the tail fin. That one body plan serves very different lives, from open-water swimmers and seabed dwellers to outright parasites. Size spans from Grammanoides opisthodon, about 5 cm long, to Lamprogrammus shcherbachevi, which reaches 2 metres.
The deepest-living member gets the headlines, yet plenty of species stay shallow, especially around coral reefs, and a handful live in fresh water. Most are tropical or subtropical, but the order's range stretches north to the Greenland coast and south into Antarctica's Weddell Sea. Alongside the Italian Pastorius, the oldest fossils include several species of the early cusk-eel Ampheristus, found in the United States and Germany.
Current schemes sort the order into families that include the cusk-eels, named by Rafinesque in 1810; the bearded cusk-eels of 1838; the pearlfishes, described by Poey in 1867; the viviparous brotulas of 1861; the false brotulas, named in 1968; and the deepsea cusk-eels, separated as a family only in 2024.
Reproduction divides the order neatly. Most species lay eggs, but the viviparous brotulas and their relatives give birth to live young and appear to form a single natural group, whereas the egg-laying suborder was long a paraphyletic grab bag until recent revisions tidied it. Two families once filed here, the tadpole cods and the eucla cods, have been moved to the cod order, and the tadpole cods are now merged into the cod family itself.
Source: Ophidiiformes
