The suction disc of remoras grips uneven surfaces with a combination of suction and friction.

Remoras, or shark suckerfish, are a species of perch-like fish that have a mutualistic relationship with sharks, turtles, rays and other large ocean species. The front dorsal fin of remoras has become adapted into a sucker. This sucker allows a remora to passively attach to its much larger host, catching a ride with it and giving it access to any scraps of food the host may drop. In return, the remora also eats parasites that attach to the host’s skin, keeping it clean and healthy.

Image: Elias Levy / CC BY - Creative Commons Attribution alone

Remora use their suckers to catch a free ride from sharks and other powerful swimmers larger than themselves.

Remora suckers have a number of features that make them particularly good for attaching to uneven surfaces moving through water. The suckers have thick fleshy lips that alter their shape to contact rough surfaces, creating a tight seal. Inside the sucker are lamellae, parallel rows of peaks and troughs that run side to side. Each lamella is tilted backwards towards the fish’s tail and its top is covered in tiny blunt-ended spinules that increase friction. As the host swims forward, the remora slips back and the spinules engage with the host’s skin, increasing friction and better holding the remora in place. Alternatively, if the remora swims forward relative to its host, the spinules disengage and the sucker detaches.

The strength of the sucker attachment is so strong that remoras have been used to catch turtles: a cord is attached to the tail of the fish, which swims towards the turtle and attaches. Hauling on the cord brings back both the remora and its host.

Image: Jonathan Couch / Public Domain - No restrictions

Drawing of a remora from the 1877 book “History of the Fishes of the British Isles”

Last Updated July 23, 2019