Definition of "butterfish"

Any of various species of fish having a slippery mucous coating, especially

1. Perciform fish of the family Stromateidae, including the genera Pampus, Peprilus and Stromateus.  examples

2. A rock gunnel, Pholis gunnellus, an eel-like fish found in the intertidal and subtidal zones of the North Atlantic.  examples

3. The New Zealand fish Odax pullus, also known as greenbone.  examples

4. (obsolete) The Murray perch, Oligorus mitchelli; an Australian perciform fish of Murray river, now known as trout cod, Maccullochella macquariensis , .

(informal) A sablefish (Anoplopoma fimbria).  examples