One common observation that sparks curiosity is the sight of smaller fish swimming closely alongside sharks. This phenomenon highlights a unique example of how marine life can coexist, often in surprising ways, forming partnerships that benefit at least one of the parties involved.
Meet the Shark’s Traveling Companions
The smaller fish often seen with sharks include pilot fish and remoras. Pilot fish, characterized by their distinct striped patterns, typically swim near the shark’s head or alongside its body without direct attachment. Remoras, also known as suckerfish, are recognizable by a unique oval-shaped suction disc located on the top of their heads. These fish use this specialized disc to firmly attach themselves to the shark’s skin, often on its underbelly or sides.
A One-Sided Partnership
The relationship between sharks and these accompanying fish is considered commensalism. In commensalism, one organism benefits from the interaction while the other is neither significantly harmed nor helped. Sharks do not receive direct benefits from the presence of pilot fish or remoras. The shark’s large size and constant movement create an environment that these smaller fish exploit for their own survival.
Why This Arrangement Works for the Fish
The fish accompanying sharks gain several advantages. They benefit from readily available food scraps from the shark’s meals, acting as a cleanup crew for their larger companion. The presence of a large predator like a shark offers the smaller fish protection from their predators, as few other marine animals would approach a shark to attack its companions. Remoras save energy by hitching a ride, avoiding expending energy to swim long distances. Pilot fish also conserve energy by swimming within the shark’s slipstream, using the water currents created by the shark’s movement.
How Remoras Hitch a Ride
Remoras possess a specialized adaptation for attachment: a modified dorsal fin evolved into a powerful suction disc. This oval-shaped disc, located on the remora’s head, features a fleshy outer lip that creates a tight seal against the host’s surface. Inside the disc are rows of lamellae, thin, flexible structures embedded with tiny, tooth-like spinules. When the remora raises these lamellae, the spinules grip onto the host’s skin, creating friction and suction by expelling water from the disc, ensuring a strong and secure attachment without causing harm to the shark.