Remora fish, often called remoras, are known for their distinctive ability to attach themselves to larger marine animals. This unique hitchhiking behavior highlights a specialized adaptation within marine ecosystems.
Understanding Remora Fish
Remora fish are slender, elongated ray-finned fish belonging to the family Echeneidae, which includes eight known species. Their bodies are smooth and covered with small cycloid scales, often displaying colors ranging from brown to black or grey. Remoras vary in size by species, generally measuring between 30 to 110 centimeters (12 to 43 inches) in length.
The live sharksucker (Echeneis naucrates) is among the longest, reaching up to 110 cm, while the white suckerfish (Remora albescens) is shorter, with adults typically around 30 cm. These fish are found globally in warm temperate and tropical oceans, often inhabiting open ocean environments. They are classified within the order Carangiformes, which also includes other elongated fish like cobia and dolphinfish.
The Unique Suction Disc
The specialized suction disc on the top of a remora’s flattened head is its most distinguishing feature. This oval-shaped disc is a modified first dorsal fin, featuring slat-like structures that can open and close to generate powerful suction. The disc’s outer edge is lined with a soft, fleshy lip that forms a leak-proof seal against the host’s surface.
Inside the disc are multiple rows of paired, transverse plates called lamellae. Remoras can raise or lower these lamellae to create a pressure difference and enhance suction. These lamellae are equipped with tiny, spiky mineral structures called spinules. The spinules grip into the microscopic crevices of the host’s skin, generating friction that prevents slippage and allows the remora to maintain a firm hold even on various surface textures, from rough shark skin to smooth dolphin skin. This intricate mechanism allows them to attach firmly without causing harm to their hosts.
Life with a Host
Remoras are known for their unique relationship with larger marine animals, including sharks, rays, whales, sea turtles, and even boats. This interaction is described as commensalism, where the remora benefits while the host is generally unaffected. The primary advantages for the remora include free transportation, reducing their energy expenditure for swimming, and increased access to food sources.
Hosts also provide remoras with protection from predators and ensure a constant flow of water over their gills, which is necessary for respiration. While typically commensal, some interactions might lean towards mutualism, as remoras clean parasites and dead skin cells from their hosts, providing a cleaning service. This removal of irritants can benefit the host, though some studies suggest that the remora’s presence can create hydrodynamic drag, slightly impacting the host.
Diet, Lifespan, and Conservation
The diet of remora fish is diverse and dependent on their association with hosts. When attached, they primarily feed on leftover food scraps from their host’s meals. They also consume external parasites, dead skin, and algae from the host’s body.
When free-swimming or detached from a host, remoras may feed on small invertebrates and plankton by passively filtering water through their mouths. The lifespan of remoras in the wild typically ranges from 2 to 8 years. Seven of the eight remora species are classified as “Least Concern” by the International Union for Conservation of Nature (IUCN). However, ecologists are concerned that remora populations could face threats if the populations of their preferred host species, particularly sharks, continue to decline globally.