The ocean holds many wonders, including the intriguing relationship between large marine animals and a smaller fish that often accompanies them. This phenomenon, commonly observed with sharks, sparks curiosity about this companion and their aquatic alliance. These fish are not merely following; they are actively attached, moving seamlessly with their colossal hosts through vast ocean expanses.
Identifying the Fish and Its Attachment
The fish frequently seen attached to sharks is the remora, also known as a sharksucker or suckerfish. Its unique feature is a specialized first dorsal fin, evolved into a powerful, oval-shaped suction disc on its head. This organ allows the remora to adhere firmly to smooth or rough surfaces of larger marine animals.
The suction disc operates through a specific mechanism. Its outer edge features a fleshy, soft rim that creates a tight seal against the host’s skin. Inside this disc, rows of movable, slat-like structures, called lamellae, can be raised to generate a vacuum. These lamellae contain spinules, which enhance friction and prevent slippage, even on rough surfaces like sharkskin. The remora can increase suction by sliding backward and release itself by swimming forward, demonstrating its ability to attach and detach at will without harming its host.
The Symbiotic Relationship
Remoras attach to sharks for several reasons, primarily benefiting from transportation, food, and protection. By hitchhiking, remoras conserve energy they would otherwise expend swimming. This free ride provides access to diverse feeding grounds across the ocean.
A major food source for remoras includes scraps of prey leftover from the shark’s meals. They also consume ectoparasites found on the shark’s skin. Being attached to a large predator like a shark offers the remora protection from its own potential predators. The relationship between a remora and a shark is considered commensalism, where the remora benefits significantly, while the shark is largely unaffected or experiences minimal impact. Some research suggests the remora’s cleaning of parasites might offer a slight advantage to the shark, though this benefit is often debated and considered minor compared to the remora’s gains.
Beyond Sharks: Other Hosts
While often associated with sharks, remoras are not exclusive to them. They attach to a variety of other large marine animals. Common hosts include whales, sea turtles, and manta rays. Some remora species also attach to smaller fish like tuna and swordfish, and occasionally to inanimate objects such as boats or divers.
The reasons remoras choose these diverse hosts are consistent with the benefits derived from sharks. These large animals provide transportation, allowing remoras to conserve energy. They also offer access to food sources, whether through discarded meal fragments or by providing a surface for parasitic growth. The size of these hosts also offers protection from predators, allowing the remora to thrive.