Remoras or suckerfish are elongated brown fish that grow to 1–3 feet long. Their distinctive first dorsal fin takes the form of a modified oval sucker-like organ that creates suction and takes a firm hold against the skin of larger marine animals. Remoras sometimes attach to small boats. They swim well on their own, with a sinuous motion.
Some remoras associate primarily with specific host species. Remoras are commonly found attached to sharks, manta rays, whales and turtles. Smaller remoras also fasten onto fish like tuna and swordfish, and some small remoras travel in the mouths or gills of large manta rays, ocean sunfish, swordfish, and sailfish.
The relationship between remoras and their hosts is most often taken to be one of commensalism. The host they attach to for transport gains nothing from the relationship, but also loses little. The remora benefits by using the host as transport and protection and also feeds on materials dropped by the host. For some remora and host pairings the relationship is closer to mutualism, with the remora cleaning bacteria and other parasites from the host.
Some cultures use remoras to catch turtles. A cord or rope is fastened to the remora’s tail, and when a turtle is sighted the fish is released from the boat. It usually heads directly for the turtle and fastens itself to the turtle’s shell, and then both remora and turtle are hauled in. Smaller turtles can be pulled completely into the boat by this method, while larger ones are hauled within harpooning range.
Because of the shape of the jaws, appearance of the sucker, and coloration of the remora, it sometimes appears to be swimming upside down. This probably led to the older common name “reversus”, although this might also derive from the fact that the remora frequently attaches itself to the tops of manta rays or other fish, so that the remora is upside down while attached.