Anoplopoma fimbria. Also known as sablefish and black cod, even though it is not a type of codfish. Sable is an oily saltwater fish with dark skin (hence the name) and white flesh, caught mainly off the west coast of North America, espcially around Alaska. At its best, sable has a mild flavor and a sublime, velvety texture. Much of the North American catch is shipped frozen to Japan, where it is eaten steamed or baked with kasu, the lees of sake.
In non-Japanese cuisine in North America, sable is best known in smoked form as a Jewish delicatessen food. Smoked sable was developed (apparently after World War II) as a substitute for smoked carp, after overfishing raised carp prices. Consequently it is prepared the way smoked carp used to be: rubbed with paprika and a little garlic. (Sam Gugino, interviewing the delicatessen owner Mark Russ Federman for Wine Spectator in November, 2001, cites an old name "chicken carp" that recalls sable's historical relationship with smoked carp.) Smoked sable is quite oily, and best eaten with breadstuffs rather than alone.
There is an unrelated fish called sable in India, better known as hilsa. Butterfish is another name used for sable, although it also refers to an unrelated Atlantic fish.