Fish that turned a dorsal fin into a suction hitchhike
Remoras, also called sharksuckers, are ray-finned fish of the family Echeneidae that grow 30 to 110 centimetres long and spend most of their lives stuck to whales, turtles, rays or sharks. Their front dorsal fin has become an oval suction disc, and fossils like Opisthomyzon show the design already emerging by the Early Oligocene.
The disc is a remodelled first dorsal fin, an oval pad crossed by slat-like ridges that open and close to generate suction and grip smooth skin. Remoras belong to the order Carangiformes and are probably closest to the cobia and the dolphinfish, other elongated members of the same suborder. The oldest remora-like fossil, Opisthomyzon from the Early Oligocene of Switzerland, already had an adhesive disc, though it sat behind the head. The earliest true remora, Echeneis carpathica, comes from rocks of similar age in Poland, and Oligoremora is known from Germany.
They are tropical open-ocean fish that turn up in cooler or coastal water only when their hosts wander there. Spawning happens in June and July in the mid-Atlantic and in August and September in the Mediterranean. Sharks, manta rays, whales, turtles and dugongs are common hosts, while smaller remoras ride tuna and swordfish and may even slip into the mouths, gills or cloacae of mantas and whale sharks. Moving over a host, a remora picks off parasites and loose skin, which can benefit both parties, but the relationship is more often classed as hitchhiking. Dolphins, for one, gain nothing and pay in extra drag.
Physiologists value remoras for studying breathing costs. At speed they let water rush through the gills, known as ram ventilation, but when slow they pump it actively. Echeneis naucrates has also served as a comparison species in research on pufferfish toxin resistance.
People in several cultures have used them as living hooks: a line is tied to the tail, the fish is released near a turtle, clamps onto its shell, and both are hauled aboard. Accounts of this fishing fish from Columbus's second voyage may be secondhand, according to Leo Wiener. Ancient writers believed remoras could halt ships; the Latin name means delay, the Greek genus name means ship-holder, and Pliny blamed one for Mark Antony's defeat at Actium.
Source: Remora
