Remoras are marine fish known for their ability to attach to larger ocean animals. They are often found riding with sharks, whales, and sea turtles. This allows them to travel vast distances across the world’s oceans.
Defining the Remora
Remoras belong to the family Echeneidae, a family of eight ray-finned fish species. They are known as suckerfish or sharksucker. Remoras have an elongated, slender body, ranging from 30 to 110 centimeters (12 to 43 inches) in length; some individuals can weigh over a kilogram (2.4 pounds). They are typically dark, with shades of black, brown, or gray. Their long, flattened head has a lower jaw that extends beyond the upper one.
The Suction Disc
The remora’s most distinctive feature is the oval-shaped suction disc on its head. This disc is an adaptation of the fish’s first dorsal fin, evolved into an adhesive organ. Its outer edge has a soft, fleshy lip that forms a tight seal against the host.
Inside, multiple rows of plate-like lamellae are present, typically numbering between 10 and 20. These lamellae have tiny, spiky spinules that provide friction and grip. The remora creates a partial vacuum by raising these lamellae, adhering firmly without harming its host. They can release themselves by swimming forward, which folds the lamellae down and breaks the suction.
A Commensal Relationship
The relationship between remoras and their hosts is considered commensal. In this interaction, the remora benefits, while the host is largely unaffected. Remoras gain several advantages from this association, including free transportation across vast ocean distances. This conserves the remora’s energy, allowing it to travel to new feeding grounds.
They also receive protection from predators by remaining close to their hosts. They feed on food scraps from the host’s meals. Additionally, remoras feed on parasites and loose skin from their host, sometimes offering a cleaning service that blurs the lines between commensalism and mutualism. Common hosts include sharks, whales, sea turtles, rays, and other large marine fish.
Where Remoras Live
Remoras are found in tropical and subtropical waters worldwide. They inhabit open ocean environments, or pelagic zones, where their hosts reside. While predominantly offshore, remoras can be seen in shallower coastal waters if hosts venture there. They are rarely observed swimming alone, highlighting their dependence on host attachment for survival and movement.