Clingfish are about 100 species of small, ray-finned bony fish found primarily in tropical marine waters. They belong to the family Gobiesocidae in the order Gobiesociformes. Clingfish are shaped like tadpoles with a wide, flattened head; they have no scales and are covered with a thick coating of slime that makes them very slippery. Clingfish are characterized by a large suction disc formed by the union of the pelvic fins and adjacent folds of flesh. This disc allows clingfish to attach themselves to the bottom and, in this way, they are able to withstand strong currents. Clingfish have a single dorsal fin and no spines. Most species of clingfish are small, about 4 in (10 cm) or less in length, but the rocksucker (Chorisochismus dentex) clingfish of South Africa may grow as large as 12 in (30 cm) long.
Clingfish are most commonly found in the intertidal zone of oceans worldwide. A number of species inhabit Caribbean waters, and about 20 species are found along the Pacific coast of North America. Among these North American species is the northern clingfish (Gobiesox meandricus) which is found from California to Alaska; this species averages 6 in (15 cm) in length. Six other species of Gobiesox inhabit the North American coastal waters of the Atlantic Ocean. The most common of these species is the skilletfish (G. strumosus), a drab, dusky fish measuring 4 in (10 cm) in length.