If you’ve ever watched nature documentaries about our oceans, you may have noticed that large marine creatures often gain the attention of clusters of small fish. Sharks are no exception.
“But sharks are predators”, I hear you say. Why would a group of small, defenseless fish choose to group around these oceanic hunters?
The main reason is protection. However, protection from predators isn’t the only reason. Many small fish species get a free meal in the process of shark clustering.
This article explores how and why certain fish species choose this seemingly dangerous way of life. Read on to discover more about the small fish that swim with sharks.
What is symbiosis?
Throughout the animal kingdom, animals form relationships with one another.
Unlike us humans, who tend to form romantic relationships, animals can form mutually beneficial relationships. This is known as symbiosis.
Symbiosis describes any interactions between two different species. Not all symbiosis is beneficial.
Some, such as parasitism or commensalism, only benefit one species involved.
Within the marine environment, symbiosis comes in all shapes and sizes. One of the most famous forms of symbiosis in the animal kingdom is sharks and small fish species.
Two of the most familiar and well-observed interactions with sharks are remoras and pilot fish.
What fish swim with sharks?
Let us examine these two species in more detail.
Just how have these fish adapted to swim with sharks?
Remoras are a type of bony fish, typically just under a meter in length. Found across all of the world’s oceans, they can tolerate vast migrations alongside their host shark.
Over millennia, the front dorsal fins of the remora have evolved to become a flat, suction cup-like organ.
This organ allows them to attach to the side or underbelly of many different shark species and other large marine animals.
This is a form of symbiosis as both the shark and the remora fish benefit.
Remoras eat any scraps of leftover food from the shark and eat pesky parasites that may cause the shark harm.
By keeping the anterior vicinity of the shark clear of debris, the likelihood of the development of detrimental organisms is reduced.
Remoras also consume pesky parasites that feed off the sharks.
These parasites, if left unchecked, could cause severe health complications for the shark.
The remora also receives protection from predators and convenient transportation across the ocean.
With the rather nifty ability to attach to the shark via suction, the energetic demands of the remora are reduced.
Pilot fish are instantly recognizable, with their blue bodies and striped-black markings.
Similar to the remora, they have adapted to travel vast distances across the ocean alongside shark companions.
Unlike remoras, however, pilot fish take the relationship one step further and enter the mouths of sharks.
Unfortunately, sharks can’t just nip down to the local dentist. Instead, they enlist the help of the pilot fish.
These fish nibble away at any trapped morsels of food found in the teeth of sharks, as well as clearing out any parasites found within the mouth.
Pilot fish also help rid sharks’ gills of any unwelcomed hitchhikers, such as copepods.
Sharks need a continuous flow of water over their gills to obtain oxygen. Any obstacle or intrusion may negatively affect the shark.
Within tropical coral reef habitats, the small cleaner wrasse can be found.
Unlike the other two species, they don’t travel great distances alongside sharks. Instead, they wait at designated “stations” for sharks, and other large marine creatures, to come in for a service.
The cleaner wrasse is small enough to reach those hard-to-get places that other species miss.
They expertly remove parasites, dead skin and other nasties from clients’ bodies.
Studies have shown that the overall health of the coral reef systems – diversity of life, health and size of species – was higher than reef systems with no recorded cleaner wrasses.
To see a cleaner wrasse in action, watch the video below.
Do smaller fish face threats from sharks?
The relationship between certain fish and shark species most definitely hasn’t developed overnight.
Symbiosis is an evolutionary tactic that has taken thousands, if not millions, of years to develop.
In this time, many shark species seem to understand the benefits they reap from having schools of small fish swimming around.
However, it seems not all sharks are completely onboard with this relationship.
Certain species, such as the lemon and sandbar shark, have often been observed displaying aggressive behavior to any smaller fish that attempts to swim alongside the shark.
There have even been instances of sharks devouring the tagalongs.
On rare occasions, opportunistic hunters, such as reef sharks, may snag a nearby fish or two. However, this has seldom been recorded.
Even if the shark is starving, smaller fish are just too quick and agile; they can outmaneuver the shark in a heartbeat. For a shark, it’s just not worth the energy or hassle to chase after these smaller fish.
On the surface, small fish that swim close to sharks seem to be playing a risky game. After all, sharks are one of the most feared predators on the planet.
However, coevolving with one another, an incredible symbiotic relationship has emerged.
The ocean is a scary place, especially if you’re a small fish. Just think of all those predators out to get you.
By staying close to sharks, fish not only gain vital protection from predation, but they also gain a free meal in the process.
The relationships observed between small fish and sharks have far-reaching beneficial effects within the reef community.