The cusk-eel family, Ophidiidae, is a group of marine bony fishes in the order Ophidiiformes. The scientific name is from the Greek ophis meaning "snake", and refers to their eel-like appearance. True eels, however, diverged from other ray-finned fish during the Jurassic, while cusk-eels are part of the Percomorpha clade, along with tuna, perch, seahorses, and others. Unlike true eels of the order Anguilliformes, cusk-eels have ventral fins that are developed into a forked barbel-like organ below the mouth. In the true eels by contrast, the ventral fins are never well-developed and usually missing entirely.
They are found in temperate and tropical oceans throughout the world. They live close to the sea bottom, ranging from shallow water to the hadal zone. One species, Abyssobrotula galatheae, was recorded at the bottom of the Puerto Rico trench, making it the deepest recorded fish at 8,370 m (27,460 ft).
The largest species, Lamprogrammus shcherbachevi, grows up to 2 m (6.6 ft) in length, but most species are shorter than 1 m (3.3 ft). Unlike their close relatives, the viviparous brotulas of the family Bythitidae, they are egg-laying, and the larvae live amongst the plankton, relatively close to the surface.