A curious sight occasionally emerges in the ocean: a smaller fish seemingly glued to a larger marine animal, often a shark. This remarkable attachment sparks immediate questions about how such a connection is formed and maintained, and what purpose it serves. The presence of these oceanic hitchhikers highlights a unique survival strategy in the marine world.
Meet the Remora
The fish that commonly attaches to sharks belongs to the family Echeneidae, collectively known as remoras, or sometimes “suckerfish” or “sharksuckers”. These ray-finned fish are characterized by their elongated, slender bodies, typically dark grayish-brown to black in color. Remoras vary in size depending on the species, generally ranging from 30 to 110 centimeters (about 12 to 43 inches) in length.
Remoras possess a distinct flattened head, with a lower jaw that extends beyond the upper jaw. Their most striking feature is a specialized oval-shaped organ on top of their head. This unique adaptation enables their ability to adhere to other marine creatures.
The Suction Power
The remora’s ability to stick firmly to its hosts stems from a highly specialized structure on its head: a modified first dorsal fin that has evolved into a powerful suction disc. This oval disc is composed of a fleshy outer lip that forms a leakproof seal against the host’s surface. Within this disc are multiple rows of slat-like structures, or lamellae, which can be raised and lowered by the remora.
These lamellae contain numerous spiky, mineralized projections called spinules. When the remora positions its disc, these spinules grip into the microscopic crevices of the host’s skin, generating friction that prevents slippage.
By pumping water out from the disc’s interior, a pressure difference creates a strong vacuum effect, securing the remora in place. This mechanism allows remoras to remain affixed even as their hosts swim at high speeds or leap from the water.
Life Aboard a Host
The relationship between a remora and its host, such as a shark, is commensalism. The remora benefits significantly, while the host is generally unaffected or experiences only a minor impact.
Remoras gain several advantages from this association, primarily transportation, which allows them to travel vast distances without expending their own energy.
Beyond transportation, remoras also access food resources. They feed on scraps dropped by their host, or consume external parasites and dead skin. This cleaning behavior can benefit the host by reducing irritants and maintaining skin health.
While sharks are common hosts, remoras also attach to a variety of other large marine animals, including whales, sea turtles, rays, and even boats. The attachment is non-damaging, and remoras can detach and reattach as needed, allowing them to switch hosts or briefly swim independently.