Overview

Remoras, commonly called suckerfish or sharksuckers, are elongated marine fishes in the family Echeneidae. They are best known for a flattened suction disk on the top of the head that allows them to attach to larger marine animals for transport, protection and access to food. For a general introduction to their appearance and classification see appearance and taxonomy.

Physical characteristics

The characteristic suction disk is formed from modified elements of the dorsal fin and bears a series of parallel lamellae; the remora can open, close and reposition the disk to attach or detach from a host. The body is streamlined and usually dark or mottled, helping to reduce drag while attached. Most species are relatively small compared with their hosts, although size varies among species.

Attachment, movement and benefits

Remoras use the disk to cling to sharks, rays, turtles, large bony fishes and sometimes boats. Attachment provides transport and protection from predators, and lets the remora travel long distances with little energetic cost. Hosts gain variable benefits; remoras can remove ectoparasites and dead skin and may reduce parasite loads on the host (host skin). However, hosts can also incur minor costs such as increased drag. See notes on typical hosts at sharks and other hosts.

Diet and ecological role

Remoras feed on scraps of food dropped by their host, free-swimming prey they encounter, and on ectoparasites such as small crustaceans that inhabit the host's skin or mouth. Because they often consume parasites and debris, their association with hosts is often described as mutualistic in some contexts but is commonly classified as commensalism on a spectrum of interactions. For information on the parasites remoras consume see parasites.

Reproduction and life cycle

Remoras are oviparous; eggs and larvae are planktonic, drifting in the open water until juveniles find hosts or suitable habitat. Young remoras may attach to floating objects or host animals as soon as they are capable of using their adhesive disk.

Taxonomy and research

Remoras belong to the family Echeneidae and have been placed historically in the perch-like order Perciformes; some modern classifications treat their higher-level placement differently, reflecting ongoing revisions in fish systematics (order Perciformes and related classifications). Their unique adhesive anatomy and host associations make them subjects of interest in studies of symbiosis, hydrodynamics and bio-inspired adhesion.

Human interactions

  • Remoras are harmless to humans and are sometimes seen attached to boats or divers.
  • The suction disk has inspired engineering and adhesion research.
  • Because their relationship with hosts varies, remoras are frequently cited in discussions of ecological interactions and symbiosis; further reading on the broader context is available at appearance and taxonomy and commensalism.