Deadly Fish: The 10 Deadliest Fish In The World

Written by Hannah Ward
Updated: December 26, 2021
Image Credit Ramon Carretero/Shutterstock.com
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With more than 35,000 species of fish in the world today, it’s not surprising that there are some deadly ones amongst them.  However, when we think of deadly fish we probably instantly think of huge sharks that can kill with one bite, but surprisingly, some of the deadliest fish are actually some of the smallest.  Some fish contain enough poison to kill an adult in less than an hour – and not all of them have an antidote!  Here we’ll discover the deadliest fish in the world, both large and small.

10. Candiru

Candiru are small but deadly, with a length of around 1 inch, and are without a doubt a fish you want to avoid at all costs.  They are a parasitic freshwater catfish that are native to the Amazon Basin and are difficult to spot due to their translucent body.  Candiru feed on blood and have a small head and body which can swell after they have had a meal.  Although they usually live in the gills larger fish they have been known to swim up into the urethra of humans.  Once they have entered the urethra they are difficult to remove as they have backward pointing spines on their gills. Candiru then feed on the blood and mucous membranes and lay eggs in the bladder, eventually causing death unless removed.

9. Goliath Tigerfish

Goliath tigerfish have teeth 1 inch long

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The goliath tigerfish is known as the most dangerous fish in Africa.  These freshwater fish are found in the Congo River Basin and are highly predatory, feeding on literally anything they can catch.  Goliath tigerfish are incredibly fearsome with their large, protruding teeth and are known as the African equivalent of a piranha.  In fact, Goliath tigerfish are the only freshwater fish in Africa that are actively known to attack humans.  With the ability to reach a whopping 130 pounds, these fierce predators often attack unsuspecting swimmers.  Each tooth is around 1 inch long and there is never any worry about them losing any as they even have a set of replacement teeth for any that are lost or broken.

8. Wels Catfish

Dealiest Fish - Wels Catfish
The wels catfish can can reach up to 16 feet in length!

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Wels catfish are huge freshwater fish that can reach an incredibly 16 feet long.  These giants are found in lakes and rivers in Europe and are easily recognized by their broad, flat head and huge mouth.  Wels catfish eat a range of worms, insects, fish, rodents, frogs, and birds.  Their mouths contain rows of small but incredibly sharp teeth, and there has been numerous reports of this fearsome fish attacking and killing people, usually fishermen or unsuspecting swimmers.

7. Moray Eel

Largest eels - green moray
Moray eels are incredibly vicious when disturbed

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Despite looking more like a snake, moray eels are actually fish and are incredibly dangerous.  There are around 200 species of moray eels worldwide and although most live in the sea, some are found in freshwater.  Most moray eels can reach 5 feet and don’t have pectoral fins which some people mistake them for snakes.  Moray eels eat mainly squid, octopus, crustaceans, and other fish.  They often reside in rocky crevices and divers are often attacked by them.  Moray eels are incredibly vicious when disturbed and attack with a lightening fast reflex.  Their teeth are exceptionally strong and sharp and are angled backwards to prevent prey from escaping.  This makes their bites extremely painful and wounds usually bleed heavily.  Moray eels carry a toxin in their slime and mouth which destroys red blood cells. This toxin is thought to be the reason why their bites are so serious.

6. Boxfish

A yellow spotted boxfish – boxfish release poison through their skin into the surrounding water

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Boxfish are very similar to pufferfish (next on our list), although not quite as lethal.  Their size ranges between 10 and 24 inches, depending on the species, and they usually inhabit rocky and coral reefs in the Indian, Pacific, and Atlantic oceans.  They are distinguished by their box-shaped bodies and honeycomb patterns on their skin.  Boxfish mainly eat algea, worms, and small fish and they have an incredibly defense mechanism to ward off predators.  They release a toxin called ostracitoxin through their skin into the surrounding water which is poisonous to anything in the vicinity.  This can be particularly harmful to humans as it breaks down red blood cells.  In addition, some boxfish are deadly if eaten uncooked. However, most people prefer to avoid eating them entirely because of their similarities to pufferfish.

5. Pufferfish

Yellowspotted Pufferfish puffed up to defend itself.
Pufferfish are one of the deadliest fish in the world

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Easily one of the most dangerous fish in the world is the pufferfish.  There are more than 120 species of pufferfish and they can range in size from 1 inch long to more than 2 feet.  Pufferfish are found in most tropical and subtropical waters and they inflate into a ball when they are threatened or disturbed, hence their name.  They have large spines on their skin which are only visible when they are puffed up.  However, looking fierce is not their only weapon as most pufferfish contain tetrodotoxin.  Tetrodotoxin is a powerful poison that is 1,200 times more deadly than cyanide.  The powerful poison is located in the liver, ovaries, and intestine of pufferfish, although even touching them is dangerous, and one fish contains enough toxin to kill 30 adult humans.  What’s even more chilling is that there is no known antidote.

Pufferfish are also a Japanese delicacy known as fugu.  Chefs must undertake rigorous training and hold a special licence before they are allowed to prepare the food.  Even the slightest mistake could be deadly and diners are literally dicing with death.  The tiniest amount of poison can cause paralysis and death, although the unlucky person is concious until the end.

4. Great White Shark

Great white shark in the ocean
Great white sharks have a bite force of around 18,000 newtons

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No list of deadly fish would be complete without the great white shark.  Great white sharks are the most notorious sharks and are responsible for the highest number of unprovoked attacks on record.  With around 300 teeth and an estimated bite force of around 18,000 newtons, the great white is a fierce predator.  Great whites have an average length of 15 feet, but some reports record lengths exceeding 20 feet, such as the great white shark “Deep Blue” that weighs an estimated 5,000 pounds!.  These incredible predators have an excellent sense of smell and can detect blood from a quarter of a mile away.  Great white sharks are located in the coastal water of most major oceans and regularly eat fish, whales, dolphins, sea turtles, and seals.

Many scientists believe that great whites do not intentionally attack people, but are simply doing a “taste test”.  This is when they leisurely swim up to someone, often someone surfing, and take a bite to see if they are edible. This is greatly different to when they are intentionally hunting and rocket up to their prey from beneath and land a devastating bite.  Unfortunately for us humans, even a taste test can be deadly.

3. Oceanic Whitetip Shark

These huge sharks are believed to have killed more people than great whites

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Oceanic whitetips inhabit tropical seas around the world and are distinguished by their white-tipped fins.  Although the great white shark, tiger sharks, and bull sharks have far more recorded attacks on humans, the oceanic whitetip is generally believed to have killed the most people.  This is because they frequently pick off the survivors of shipwrecks and downed planes.

Oceanic whitetips are most famous for their attack on the survivors of a US navy ship during World War II.  The USS Indianappolis was sunk on 30th July 1945 by a Japenese submarine.  Approximately 890 crewmen were stranded in the water for four days while they awaited rescue.  Only 316 survived.  According to survivor reports, towards 150 people were killed by oceanic whitetips, making it the deadliest shark attack in history.  Oceanic whitetip sharks are also attributed to a large loss of life when RMS Nova Scotia sunk in 1942.

2. Lionfish

Lionfish
Stunning lionfish blow jets of water at their prey to confuse them

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Lionfish are incredibly venomous fish that are native to the Pacific Ocean, although they have now invaded many other oceans.  They reach around 18 inches long and are characterized by their bright colors.  Lionfish can have red, white, or black bands and have spiky fin rays which are venomous.  They mainly feed on small fish and invertebrates and swallow their prey whole.  Amazingly, they blow jets of water at their prey to confuse them before they capture them.  Moray eels and sharks are some of the few known predators of these fish.  Their stings can cause extreme pain, vomiting and breathing difficulties.  Although lionfish stings are not usually fatal to adults they are much more dangerous to children, elderly, or anyone who suffers an allergic reaction.

1. Stonefish

10 Most Venomous Animals - Reef stonefish lying in wait of prey
Lying in wait – stonefish have excellent camouflage

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The deadliest fish in the world is the stonefish, which has some serious ability to cause harm!

Stonefish are around 14 to 20 inches long and the same in width due to their extremely wide pectoral fins.  They are found in tropical waters – including the Indian Ocean, Pacific, Red Sea, and the Great Barrier Reef.  Stonefish have crusty skin and razor-like spines and contain enough toxin to kill an adult in less than an hour, which makes them the world’s most venomous fish.  They are ambush predators who feed from the bottom of the sea bed where they camouflage themselves on the floor.  Their crusty skin blends in with the rocks and sand, hence their name.

Stonefish deliver venom through the extremely sharp spikes on their back. This is so that they are protected from above when they sit on the sea bed.  Anti-venom is available but it needs to be administered quickly as paralysis and death can occur quickly.  Surprisingly, their venom is only a defense mechanism and stonefish don’t actually use it to kill their prey with.  Instead, they strike with their huge, powerful jaws and swallow their prey whole.  Stonefish eat reef fish and small invertebrates. Sharks, rays, and large sea snakes are their only predators.

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About the Author

I'm an avid animal lover, and when not writing I can be found on my farm surrounded by dogs, horses, and sheep.