Species in the Spotlight: nature’s ultimate hangers-on

Rather than avoiding sharks, remoras stick – literally – to their sides.

Most creatures flee from sharks. Remoras stick – literally – to their sides. These fish are nature’s ultimate hangers-on, saving valuable energy by latching onto their hosts and feeding off the scraps they leave behind.

Forming attachments

Eight species of remora – sometimes known as suckerfish – make up the family Echeneidae. All are slim bony fish, brown, black or grey in colour, that are unremarkable apart from a strange oval structure on top of their head. This organ, the suctoral disk, is a modification of the spiny dorsal fin.It comprises 22–26 slat-like structures that can open or close to provide suction.

Remoras
The suctoral disk allows remoras to attach themselves to larger creatures © Gary Westphalen, Shutterstock

A remora swims up to a large marine creature, such as a shark, whale or turtle, and uses this disk to attach itself. It then hangs on for the ride, feeding from its host’s leftovers or making short sorties after small marine titbits. By sliding backwards against the skin of its host it can increase the suction, locking on tighter. Conversely, by sliding forwards it can release itself.

Different species attach themselves to different hosts, and some may remain in place for up to three months.The smaller species may latch on inside the mouths of large fish, such as mantas or sunfish, where they can more easily hoover up scraps.It is not clear how much the host benefits from the arrangement – although the remora may remove bacteria and parasites from its skin.

Tropical wanderers

Remoras are found primarily in tropical seas, although they may hitch a ride on a host that wanders into more temperate waters. Spawning occurs during the spring and early summer. The eggs are fertilised externally and their tough shell keeps them from drying out, even if washed up on land. Hatchlings are approximately 5mm long. They live as part of the plankton for the first year, until they develop a sucker disk at about 1cm. At 3cm long they are fully formed, and head out to find the nearest convenient host.

Remoras
Traditional fishing communities sometimes use remoras to catch turtles

Some traditional fishing communities, notably in the Indian Ocean, have used remoras as ‘fishing fish’. They attach a line to one they have captured and then, when they come within sight of a turtle, release it into the sea. The remora usually swims straight to the turtle and attaches itself, whereupon the fishermen are able to drag in their catch – or at least bring it within harpooning range.

At a glance

Length: 30–90cm (varies by species)

Food: parasites; copepods; any leftover scraps from host

Reproduction: spawns in open ocean; hatchlings find host at 3cm long

Habitat: warm and tropical oceans; may be carried by hosts into more temperate zones

Distribution: worldwide

Status: Least Concern (all species)