Nobody likes a freeloader, and if you’ve ever seen a shark cruising majestically in the ocean, you may have noticed one or more strange-looking fish getting what looks like a freeride.
However, before you rush to judgment on the fish hanging off the shark’s belly, let’s look at the remoras and shark’s relationship and see if it’s as one-sided as it first appears.
We’re going to see that while the remoras get plenty of benefits, including a free lift, protection, and food, these sucker fish on sharks also offer cleaning services to their host in what is called a mutualistic arrangement.
Remoras (family Echeneidae) are a relatively small fish found in tropical seas which have developed an incredible suction cup that allows them to grip onto their host and get free transportation.
As we look at how sharks and remoras live together, we’ll discover everything about their fascinating relationship and its benefits to both species.
Why Do Fish Follow Sharks?
There are three main reasons why fish follow sharks: protection, food, and saving energy.
The open ocean doesn’t offer a lot of places to hide from predators, so some fish have adapted to take advantage of what is available to them.
By sticking close to a shark, the smaller fish are safer from predators which might otherwise hunt them.
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While the shark may not deliberately give its protective services, it doesn’t seem bothered by the smaller fish and isn’t interested in wasting the energy to catch such a small snack.
Hanging around a shark may also give its followers an easy meal. Sharks are messy eaters, and small pieces of food usually get missed, which can be grabbed by the passengers.
Small fish may also pick dead skin and parasites off their host, which feeds them and benefits the shark.
Finally, following a shark may save the small fish energy.
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By swimming next to the relatively giant shark, smaller fish can make headway easier than if they were swimming alone.
Before we look at the remora specifically, it’s worth clearing up the difference between them and other fish that you might have seen following sharks.
As we will see shortly, remoras are unique in that they latch onto the shark with their suction cup and get carried along.
Other fish follow sharks, but they must swim to keep up.
What Are the Fish That Swim With Sharks?
In addition to the remora, there’s one other fish you’ll commonly see swimming with sharks, the pilot fish (Naucrates ductor).
Pilot fish are a type of jackfish found in temperate, warm, and tropical open oceans.
While juvenile pilots will seek shelter amongst algae, jellyfish, and marine debris, they’ll quickly find a larger host to swim with once they get bigger.
Pilot fish swim with sharks, turtles, whales, and rays. Still, they’re probably most commonly associated with the oceanic white tip shark (Carcharhinus longimanus), whose slow, but constant swimming style suits the pilot fish perfectly.
The shark gives the pilot fish protection, and they get to pick off uneaten pieces of food and save energy as they swim together.
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Pilot fish have also been seen cleaning the shark’s gills of parasites and picking food fragments from their mouths.
Scuba divers often see oceanic whitetips with so many pilot fish that it looks like the shark is swimming in a dark, shimmering cloud.
However, the shark’s behavior doesn’t seem affected and the oceanic just gets on with its business, apparently unconcerned.
What Is the Relationship Between Sharks and Remoras?
The shark and remora relationship is pretty similar to the shark’s one with the pilot fish.
The smaller fish gets protection and food while it keeps the shark clean.
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However, in terms of free transportation, the remora gets an even easier life thanks to its unique adaptations.
So, let’s start by looking at what a remora is and why it’s such a unique fish.
What is a Remora Fish?
Remoras live in the open ocean and are mainly seen in warm and tropical waters.
Their distribution extends during the summer months as sea temperatures rise and their hosts travel further from the equator.
They are eight different remora species, and they typically get to about 30–110 cm (12–43 in) in length.
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Most are grey, green, or blue in coloration to match their hosts.
The unique feature of the remora is the sucker-like organ on top of the head.
The suction cup has formed from the fish’s front dorsal fins and has slats that can open and close to suck against the skin of a larger animal.
Remoras are usually seen hanging from a shark’s belly, but they will also hitch a ride with manta rays, turtles, dugongs, and whales.
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Young or small remoras are seen on tuna and other larger fish, or even in the mouths of manta rays, sunfish and sailfish.
It’s even been known for lonely remoras to attach themselves to scuba divers!
Shark and Remora Relationship Benefits
So, why do remoras attach themselves to sharks?
Do the sharks get any benefit from the remoras and sharks relationship?
A symbiotic relationship or symbiosis is where two organisms live together.
There are several symbiotic relationships, including mutualistic, commensalism, and parasitic symbiosis.
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The symbiotic relationship between remoras and sharks is mutualism because the two species benefit from the existence of each other.
We’ve already seen that, like the pilot fish, remoras eat scraps of food and get protection from being with the host shark.
The suction cup lets the remora save a lot of energy as it gets free transportation from the shark instead of swimming.
The organ has evolved so that the faster the host animal swims, the tighter the cup grips on as the remora is pushed backward.
To release itself from the shark’s belly, or wherever it’s attached, the remora just needs to swim forward.
Finally, the remora even gets to breathe more easily while the shark carries it.
Like many fish, the remora can breathe in two ways.
Ram ventilation is where the water passing the fish moves through its gills to provide oxygen.
Usually, this happens when a fish swims, which uses energy.
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The second way, when a fish is swimming slowly or has stopped moving, is active ventilation.
This is where the fish energetically pumps its gills to push water through them.
By avoiding active ventilation, the remora saves about 3.7 to 5.1% of its energy.
As it hangs onto the swimming shark, water passes through the remoras gills, and it gets the benefits of ram ventilation breathing for free.
So, what does the shark get from the remora?
The remora will clean irritating parasites from the shark’s skin and mouth.
Remoras will also pick uneaten food from the shark’s mouth and lose flakes of skin off their bodies which may prevent infection.
The cleaning service is thought to be so welcome a passing shark has been observed slowing down when swimming near a free remora so that it’s able to jump aboard.
While the remora undoubtedly gets nutrition from its cleaning and opportunistic feeding on scraps, scientists believe several species actually get most of their food from eating the shark’s feces.
Are Remoras Found on All Shark Species?
Remora fish tend to be found in warm and tropical waters, so they are seen on the sharks that live there. Remoras are not found on cold water shark species.
Do Sharks Eat Remoras?
Typically sharks seem to appreciate the remora’s presence. The answer to “Why do sharks not eat remora fish?” does seem to be that they understand that the relationship is beneficial.
It could also be that the remora is usually too small for the host shark to bother trying to catch.
However, shark species, including sandbar and lemon sharks have been documented acting aggressively toward remoras.
These sharks have even been seen consuming possibly beneficial remoras.
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It could be that the sharks in question were unusually hungry or just that these particular sandbars and lemon sharks find the remora just too irritating to have around.
Does the Remora Cause Any Harm to the Shark?
Typically a remora doesn’t cause any harm to the shark.
The main exception noted is that sharks have been seen with apparently harmless skin marks that the remora has sucked on especially hard.
Additionally, particularly large or numerous remoras may cause drag in the water, meaning that the shark has to expend more energy than usual.
Even if the shark doesn’t get any benefits from the remora fish cleaning services, the worst case is that the relationship is remora and shark commensalism, where the remora benefits and the shark neither benefits nor is harmed.
So when considering “are remoras parasites?”, we can say they are not because, unlike a shark parasite fish, the shark and remora relationship isn‘t getting its food at the expense of its host.
Remora Fish and Other Animals
Should you expect to see the remora fish that stick to sharks on any other animals, or is the shark and remora relationship exclusive?
Many remoras are not choosy and will hitch a ride on anything significant.
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However, some of the eight remora species seem to favor specific host animals, and not all are sharks.
The slender sharksucker (Echeneis naucrates) which tropical scuba divers commonly see is usually found riding on sharks or turtles.
However, it is also seen catching a lift on larger fish, including the napoleon wrasse (Cheilinus undulatus), and on rays like the spotted eagle ray (Aetobatus narinari).
The common remora (Remora remora), the largest species, appears to be attracted mainly to manta rays (genus Mobula) and whale sharks (Rhincodon typus).
You’ll only see the whalesucker (Remora australis) attached to whales and dolphins.
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The most common host is the blue whale (Balaenoptera musculus).
The dolphins appear annoyed by the weighty presence of the remoras and will leap from the water, trying to dislodge their passenger.
Finally, the mantasucker (Remora albescens) is generally found on manta rays and will live inside the manta’s mouth or gill cavity.
The occasional diver has experienced a lonely remora fish trying to suck onto their air cylinder or even their bodies.
Unlike tough shark skin, human skin can react to the remoras suction cup, and in rare instances the resulting scratch marks can bleed slightly.
Conclusion
The remoras and sharks’ relationship is usually regarded as being mutualism symbiosis because they benefit from the existence of each other.
The remora receives protection, a convenient food source, and saves energy as the shark carries it along.
To benefit the shark host, the remora removes parasites and other unhealthy organisms from the shark’s skin and mouth and will pick uneaten food from its teeth and loose flakes of skin which may prevent infection.
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The shark and remora relationship is one of nature’s most fascinating symbiotic relationships.
It’s just another stunning way members of the animal kingdom have evolved to live together.
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.