A frequent sight in marine documentaries and photographs is a shark accompanied by smaller fish clinging to its body. This unique association sparks curiosity about the identity of these fish and the nature of their relationship. This interaction highlights specialized adaptations and interspecies dynamics in the ocean.
Identifying the “Fish on Them”
The fish commonly observed attached to sharks are remoras, also known as “suckerfish.” These elongated, ray-finned fish belong to the family Echeneidae, which includes eight species. Remoras grow up to 43 inches long. A distinguishing characteristic is their flattened, oval-shaped sucking disc on top of their head. This unique disc, a modified first dorsal fin, allows them to securely adhere to larger marine animals.
The Nature of Their Relationship
The relationship between remoras and sharks is an example of commensalism, a symbiotic interaction where one species benefits while the other is unaffected. Remoras benefit from this association in several ways. They conserve energy through free transportation across vast ocean distances. Being attached to a large predator like a shark also provides remoras with protection from potential threats.
A benefit for remoras is access to food. They feed on food scraps left behind from the shark’s meals, acting as opportunistic scavengers. Remoras also contribute to the shark’s hygiene by consuming external bacteria, algae, or parasites on its skin and in its mouth. This cleaning service benefits the shark, and the remora’s presence does not harm the shark or impact its energy expenditure, as their streamlined bodies minimize drag.
How They Attach and Detach
The remora’s ability to attach and detach from its host is due to its specialized suction disc, which evolved from its dorsal fin. This oval disc creates a vacuum, allowing the fish to latch onto surfaces, even the rough skin of a shark. The disc features a soft, fleshy outer lip that forms a seal against the host’s surface.
Within the disc are rows of plate-like structures called lamellae. These lamellae, which can be raised and lowered by the remora, are lined with tooth-like projections called spinules. When the remora rotates these lamellae, the spinules grip into crevices on the host’s skin, generating friction that enhances the hold. This mechanism allows remoras to attach and then release themselves by swimming forward or adjusting the lamellae.
Beyond Sharks: Other Hosts
Remoras are not exclusively found attached to sharks; their hitchhiking behavior extends to a variety of other large marine animals. They adhere to whales, sea turtles, and manta rays, utilizing these hosts for transportation and feeding opportunities. Other large fish, such as tuna and swordfish, also serve as hosts for remoras. Even non-living objects like boats can become temporary attachment points for remoras.
Across all these different hosts, the nature of the relationship remains consistent. Remoras benefit from the mobility, protection, and food sources provided by their hosts, while having a minimal impact on them.