Members of the Echeneidae family, remoras and sharksuckers are slim fish that have a flat sucking disk on the top of their heads. They attach themselves usually to sharks or other fish—including marlin, grouper, and rays—but sometimes to the bottoms of boats or other objects. These hitch-hikers take effortless rides with their hosts, feeding on parasitic copepods found on the hosts’ bodies and gill chambers.

Developed from the first dorsal fin, the sucking disk consists of a series of ridges and spaces that create a vacuum between the remora and the surface to which it attaches. By sliding backward, the remora can increase the suction, or it can release itself by swimming forward.

The sharksucker (Echeneis naucrates), which averages 1.5 feet in length but may be as much as 38 inches long and can weigh up to 2 pounds, is the largest member of the family. Worldwide in distribution in warm seas, it is gray with a broad, white-edged black band down each side, tapering to the tail. It prefers sharks and rays as hosts and often enters shallow beach and coastal areas; it has been known on rare occasions to attach itself to bathers or divers.

Also cosmopolitan is the remora (Remora remora), which is common to 12 inches long and may attain a length of 34 inches. It is black or dark brown and is also found worldwide. It, too, prefers sharks as hosts. Some other species show distinct host preferences. The whalesucker (R. australis), for example, generally fastens itself to a whale; the spearfish remora (R. brachyptera) commonly attaches to billfish such as marlin.

Although often observed by anglers, remoras have no angling merits.