The remora is a marine fish famous for its unique ability to attach to larger animals like sharks, whales, and sea turtles. This behavior, known as hitchhiking, allows the remora to travel vast distances without expending its own energy. The answer is generally no, though the relationship is not entirely without cost. The remora’s specialized anatomy and the nature of its ecological partnership mean that significant injury to the host is rare.
Anatomy of Attachment: The Suction Disc
The remora’s remarkable ability to adhere to a host is due to a highly specialized organ on the top of its head, which is not a mere suction cup but a modified dorsal fin. The oval-shaped disc functions by combining the power of a vacuum seal with mechanical friction.
The outer edge of the disc is lined with a soft, fleshy lip that creates a watertight seal against the host’s skin. Inside this seal are multiple rows of bony, plate-like structures called lamellae, which can be raised and lowered by the remora. These lamellae are equipped with microscopic, tooth-like spinules that provide friction against the host’s surface.
The remora creates the vacuum by lifting the lamellae, which lowers the pressure within the sealed disc chamber. This mechanism allows the fish to remain firmly attached even when the host swims at high speeds or makes sudden movements. Crucially, because the attachment relies on a pressure differential and surface friction, the remora does not need to bite, pierce, or hook into the host’s skin.
Defining the Relationship: Commensalism
The ecological classification of the remora-host interaction is commensalism. This type of symbiotic relationship means that one species, the remora, benefits, while the other species, the host, is generally neither helped nor harmed. The remora gains three primary advantages: free transportation, protection from its own predators, and an expanded food source.
Its proximity to the host also offers a continuous supply of food, consisting of the host’s leftover meal scraps and shed skin cells. Some observations even suggest a mutualistic element, where the remora actively feeds on external parasites attached to the host, effectively providing a cleaning service.
Potential Drawbacks for the Host
While the remora does not intentionally inflict pain, the relationship can impose minor physiological costs on the host. The increase in hydrodynamic drag is the primary drawback. The presence of one or multiple remoras disrupts the host’s streamlined body shape, forcing the animal to expend slightly more energy to maintain its swimming speed.
The cumulative effect of several remoras attached to a single host can increase this drag, potentially slowing down the host. For large, fast-swimming animals like sharks, this energetic cost is likely negligible, but for smaller or already stressed hosts, the effect could be more pronounced.
The friction created by the remora’s spinule-equipped lamellae, while non-invasive, can also cause minor surface irritation. Repeated attachment and detachment in the same area may lead to localized reddening or slight surface lesions, particularly on hosts with delicate or compromised skin.