The Cyclopteridae are a family of marine fishes, commonly known as lumpsuckers or lumpfish, in the order Scorpaeniformes. They are found in the cold waters of the Arctic, North Atlantic, and North Pacific oceans. The greatest number of species are found in the North Pacific. The family name Cyclopteridae derives from the Greek words κύκλος (kyklos), meaning "circle", and πτέρυξ (pteryx), meaning "wing" or "fin", in reference to the circle-shaped pectoral fins of most of the fish in this family.
Cyclopteridae includes the following valid genera:
Lumpsuckers are named appropriately enough; their portly bodies are nearly spherical with generally drab coloration and lithic patterns. The "sucker" part refers to the fish's modified pelvic fins, which have evolved into adhesive discs (located ventrally, behind the pectoral fins); the fish use these discs to adhere to the substrate. Many species have bony, wart-like tubercles adorning the head and body; these are important taxonomic features of the family.
The simple, rounded fins are small with the exception of the broad, fan-like pectorals, which actually extend ventrally. The first of the two dorsal fins is spinous, with 4-8 spines; in some species, this fin is completely overgrown with skin and therefore not visible. While the lateral line in lumpsuckers is otherwise reduced or absent, it is well developed in the head; some species even have tubular, whisker-like external projections of the opercular canal, which is a part of the cranial lateral line system.
The relatively small mouths of lumpsuckers are lined with narrow rows of small conical teeth. The gas bladder is absent. In terms of length, lumpsuckers range in size from in the case of Eumicrotremus awae up to more than in the case of the common lumpsucker Cyclopterus lumpus.
As their appearance might suggest, lumpsuckers are poor swimmers. Most species are benthic; that is, they spend most of their time on or near the bottom. The fish are found on rocky or muddy substrates, where their colouration allows for effective camouflage.