An Evolved Engineering Marvel
In the warm oceans of the world, members of the fish family Echeneidae employ a unique survival strategy. Commonly known as remoras or sharksuckers, these fish have an anatomical feature found nowhere else in nature: a highly modified dorsal fin that functions as a powerful suction disc. This oval-shaped organ, located on the top of the head, is not a simple cup. It is a mechanism composed of a soft, fleshy lip that creates a seal and rows of slat-like structures called lamellae.
The mechanism relies on both suction and friction. The soft lip, made of highly compliant and energy-dissipating tissue, conforms to the surface of a host animal. The remora then raises the lamellae within the disc to create a negative pressure environment, generating suction. Protruding from these lamellae are hundreds of tiny, tooth-like spinules that increase friction and prevent slipping. This dual-action system is so effective that the drag created by the host swimming through the water is thought to passively increase the strength of the adhesion. Depending on the species, remoras can have between 10 and 28 lamellae in their discs, and can grow from 30 to 110 cm in length.
Life on the Move
Remoras attach to a wide variety of hosts, including sharks, manta rays, sea turtles, whales, and large bony fish. They have also been observed attached to ships and even scuba divers. The relationship is a form of commensalism, where the remora benefits without harming the host. The remora gains transportation, protection from predators, and a steady source of food. Their diet consists of scraps from the host's meals, host feces, and ectoparasites they clean from the host's skin. By removing parasites, some argue the relationship is actually mutualistic.
The adhesion is strong and easily reversible. To detach, a remora simply swims forward or curls the soft lip of the disc, a process that can take less than 240 milliseconds. This incredible biological mechanism has not gone unnoticed by engineers. Researchers are actively studying the remora's disc to develop new bio-inspired adhesives. A robotic disc modeled on the remora, weighing only 45 grams, was able to withstand a pulling force of 27 Newtons. Such technology could lead to new types of surgical clamps, sensors for underwater reconnaissance, and residue-free bandages.