Brotula

Cusk-eels are characterized by a long, slender body that is about 12–13 times as long as it is deep. 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). Their dorsal and anal fins are typically continuous with the caudal fin (with exception to a few species), forming a long, ribbon like fin around the posterior of the cusk-eel's body. This caudal fin will often be seen to be reduced to a fleshy or bony point, especially when confluent with the dorsal and anal fins. The dorsal fin to anal fin ray ratio is approximately 1.5:1, leading to the dorsal fin typically being longer than the anal. The pectoral fins of cusk-eels are typically longer than the length of their head.

Cusk-eels live 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).

Cusk-eels are generally very solitary in nature, but some species have been seen to associate themselves with tube worm communities. Liking to be hidden when they are not foraging, they generally associate themselves within muddy bottoms, sinkholes, or larger structures that they can hide in or around, such as caves, coral crevices, or communities of bottom-dwelling invertebrates, with some parasitic species of cusk-eel actually living inside of invertebrate hosts, such as oysters, clams and sea cucumbers. Cusk-eels generally feed nocturnally, preying on invertebrates, crustaceans and other small bottom-dwelling fishes.

Unlike their close relatives, the viviparous brotulas of the family Bythitidae, cusk-eel species are egg-bearing, or oviparous, organisms. While the specifics of the eggs of the family Ophidiidae are unknown, they are believed to be either spawned as individual, free-floating eggs in the open water or are placed in a mucilaginous raft, which will float for several days until they hatch into cusk-eel larvae. These larvae live amongst the plankton relatively close to the water's surface and are believed to control their metamorphoses into adult cusk-eels, dispersing over greater distances into less utilized habitats and reducing competition in concentrated areas.

While a few species are fished commercially – most notably the pink cusk-eel, Genypterus blacodes – and several species of the order Ophidiiformes are listed as vulnerable, not enough information has been gathered about Ophidiidae as a whole to determine their conservation status.