In the vast expanse of the ocean, smaller fish are often seen accompanying sharks. This intriguing natural phenomenon sparks curiosity, prompting questions about the identity of these persistent companions and the nature of their association. This unique partnership offers a glimpse into how different species can forge connections that benefit at least one party.
The Identity of the Fish
The small fish frequently observed alongside sharks are known as remoras, belonging to the family Echeneidae. These elongated marine fish typically exhibit a slender body shape, with coloration ranging from brown to black or gray. Remoras can reach lengths of up to 110 centimeters (43 inches). Their most distinguishing characteristic is a flat, oval-shaped suction disc located on the top of their heads. This specialized structure, which is a highly modified dorsal fin, allows them to adhere to larger marine animals.
A Unique Symbiotic Relationship
The interaction between remoras and sharks is primarily categorized as commensalism, a type of symbiotic relationship where the remora benefits significantly, while the shark is generally unaffected or minimally influenced. Remoras gain several advantages from this association, including convenient transportation across expansive ocean areas, allowing them to conserve energy they would otherwise expend swimming independently.
Another substantial benefit for remoras is access to food. Sharks are often messy eaters, and remoras capitalize on the scraps and leftover prey fragments that drift away during or after a shark’s meal. Beyond food scraps, remoras also consume external parasites and dead skin from their hosts, providing a cleaning service. Attaching to a large creature like a shark offers remoras a degree of protection from their own potential predators. While sharks are the most well-known hosts, remoras will also attach to other large marine animals, including sea turtles, manta rays, whales, and even oceangoing ships.
Life on the Go: Remora Adaptations and Benefits
The remora’s ability to maintain its association with large marine animals stems from its unique suctorial disc, which evolved from its dorsal fin. This oval-shaped organ features a fleshy outer lip that forms a tight seal against the host’s skin. Within the disc are rows of flexible, slat-like structures called lamellae, which create a partial vacuum and friction when raised. This allows the remora to attach firmly, even to rough surfaces like sharkskin, and endure high speeds or sudden movements. Remoras can easily detach themselves by swimming forward, which releases the suction.
Their feeding habits extend beyond scavenging; they actively consume ectoparasites and dead skin from their hosts, contributing to the host’s hygiene. Some remoras also filter plankton from the water as they travel, or even prey on small fish when opportunities arise. This diverse diet, combined with the energy saved from hitchhiking, allows remoras to thrive. The constant movement of their host also provides a steady flow of water over the remora’s gills, which is necessary for their respiration, as they cannot survive long in still water.