Sharks are predators, but their relationships with different species can go far beyond predator-prey interactions.  In fact, sharks have thriving relationships with a host of species... some are beneficial to the shark and some, not so much. These relationships are known as symbiosis. 

Symbiosis (from the Greek for “living together”) is any type of long-term interaction between two different organisms. It can be mutualistic (benefiting both organisms), commensalistic (benefits one organism but doesn’t affect the other) or parasitic (benefits one organism whilst harming the other). Sometimes symbiosis is obligatory, meaning an organism is dependent on the other for survival. Other times it’s optional when they can live independently. 

Sharks have a few different symbiotic relationships. Let’s take a look at the most common. 


Remoras are pretty hard to ignore. When watching footage or seeing photos you’d be hard pressed to miss the fish often attached sharks and rays. Growing between 30cm and 110cm (12-43 inches), depending on the species, remoras form a mutually beneficial relationship with sharks and rays.  

Also known as suckerfish, remoras have an adapted front dorsal fin which takes the form of an oval-shaped sucker. This has slat-like structures that open and close to create suction, allowing them to attach themselves to the skin of larger marine animals. The remora can adjust the level of suction - by sliding backwards the remora can increase suction, and can release itself by swimming forwards. 

Remoras on a Nurse Shark

But what benefit does this have for either party? Well, when attached to their hosts, remoras can clean their skin, feeding on any dead skin cells and parasites. In return, the remora benefits from a free meal, and protection provided by the host. They can also feed on scraps leftover by their host.  Finally, they don’t have to use as much energy to move around and pass water through their gills. This relationship suits both parties pretty well. But there are organisms that can actually cause harm to their hosts.  


Copepods are small crustaceans, some of which are parasites for sharks and rays. Clinging to the surface of a sharks on their skin, and in their gills, feeding off the shark. One unusual copepod attaches itself to the eyes of Greenland and Sleeper Sharks. The copepod permanently attaches itself to the cornea of the eye.  Dangling down from the eye and feeding on it from the inside. This can damage the shark’s vision. 

Cookie Cutter Sharks 

These sharks are actually parasites themselves! Cookiecutter Sharks grow to around 31cm – 44cm. However, they attack prey much larger than themselves. They ambush their prey, which include Humpback Whales, Whale Sharks and even White Sharks! They use their thick lips to suck onto their prey. Their sharp teeth then cut into the skin and with a twisting motion, they rip off a chunk of flesh.   

Wounds on a Grey's Beaked Whale from a Cookiecutter Shark

All these species are a crucial part of the ecosystem. Parasitism may seem nonconventional. But these relationships have occurred over millions of years of evolution and these specialists are amazing examples of how species adapt to survive. 

Banner Image ©John Bantin

Cookiecutter Image ©Wikimedia Commons