15 Most Dangerous Animals in The Ocean

The ocean covers more than 70% of the earth and is home to thousands of wild and wonderful creatures but not all of them are the kind you’d like to take home to your fish tank! Many a TV show or feature film has been centred around what can happen when humans venture into the deep and brush up against the more voracious inhabitants who aren’t in the mood for visitors but are in the mood for an impromptu snack. 

The Most Dangerous Animals In The Ocean 

The impenetrable, azure ocean can look so harmless at first glance that you’d never guess what carnage could be going on down below its shimmering depths. It’s often a case of fish-eating fish in the aquatic fight for survival but some fish are, of course, more deadly than others. Read on to find out which ocean-going animals pose the biggest threat to not only us but other sea dwellers. 


Scientific name: Sphyraena 

Barracuda Most Dangerous Animals in The Ocean
 Barracuda hovering in the strong current at Paradise Reef, 
Author: Laban712    CC0 1.0

The barracuda is a lightning-fast predator who likes to hang about near the top of the water. This large ray-finned fish is snake-like with razor-sharp fangs similar to a piranha. Colour can vary between species and includes, black, grey, green, white or blue with yellow-ish or dusky fins. Barracuda predate mainly on fish including their own species. They are hard to spot due to their silvery appearance and have intensely optimal eyesight allowing them to pick up on the slightest movement, colour or ripple at distance. 

Barracuda fatalities are rare but bites can cause deep, slashing cuts. Injuries to blood vessels, nerves and tendons are not unusual. 

The formidable barracuda frequents tropical and subtropical oceans worldwide and is more commonly near coral reefs, mangroves and seagrasses.

Blue Ringed Octopus

Scientific name: Hapalochlaena 

Blue Ringed Octopus
A blue-ringed octopus
Author: Sylke Rohrlach CC-BY-2.0

The blue-ringed octopus occupies aquatic territory from the Sea of Japan through the oceans of southern Australia across from the Philippines to Vanuatu. They like to hide under rocks or in crevices during the day and emerge at night. They are one of 4 venomous octopuses and are small, vividly coloured and extremely dangerous. They have thousands of chromatophores under their skin and these are the specialised cells which allow them to become more vivid and iridescent when threatened. They can also use this process to camouflage themselves against any backdrop. 

This vivid colour produced during a threat display is not just a facade. The colour is indicative of the neurotoxin tetrodotoxin which can potentially block nerve receptors. This substance is 1000 times more toxic than cyanide and although fatalities are rare in humans, there are a handful of cases, usually with death resulting from respiratory failure. 

Box Jellyfish

Box Jellyfish

The fact that box jellyfish are also called sea wasps and marine stingers should give you a clue as to how these deadly predators operate. Mostly found in tropical and subtropical waters, including the Atlantic, Pacific and Mediterranean seas, they can often be found near the shoreline and are known to prefer calm, shallow water. 

Box Jellyfish vary in size from almost a foot in diameter to no bigger than a thumbnail. As you may have guessed, its name comes from the box-shaped bell which is attached to highly venomous tentacles which trail behind in the water. The box jellyfish is not only extremely poisonous but is practically translucent in the water making it an invisible threat. It is estimated that between 50 and 100 people die a year from box jellyfish encounters.

Cone Snail

Scientific name: Conidae

Cone Snail
A cone snail
Author Ricahard Ling   CC-BY-3.0

Cone snails may look harmless but just one sting from this venomous crustacean is enough to cause paralysis and even death. The beautiful brown shell is often picked up by divers thinking they’ve found an attractive ornament only to find out that this little snail has a sting so powerful it can penetrate gloves!

The cone snail likes to live in fairly shallow water near coral reefs, hiding in the sand or under piles of rubble particularly in the Pacific, Caribbean and Red Seas and along the coast of Florida. The good news about cone snails is that there have only been around 36 deaths attributed to them and also, scientists are constantly studying how this remarkable venom might be used for good in the medical sphere!

Flower Urchin

Scientific name: Toxopneustes pileolus

Flower Urchin
A flower urchin
Author: Vincent C. Chen    CC-BY-3.0

Flower urchins are very widespread in the Indo-Pacific ocean and can be found in Okinawa, Japan, Tasmania and Australia. They like the sea corals and dead fragments of other echinoderms. They particularly like to bury themselves in sand or rubble and the areas of the ocean with the most debris are likely hiding places for them. There are almost 200 species of flower urchins throughout the oceans of the world. 

Although very beautiful, ranging from white, pink, purple, yellow and green – this type of sea urchin is especially dangerous due to its ability to inject a powerful venom into its predators with tiny spines which break off and remain in the target for some time eventually killing them. Flower urchins have been responsible for a number of human deaths over the years but it’s important to remember, they do not set out to harm – their attacks are purely defensive and they would much rather be left in peace!

Great Moray Eel

Scientific name: Gymnothorax javanicus

Great Moray Eel
 Moray Eel in Great Barrier Reef Marine Park
Author: Leonard Low CC-BY-2.0

The name says it all, this huge eel can reach up to 3m (9.8) in length and 30kg (66lbs) in weight and likes to live in the Indo-Pacific region, being found from the eastern coast of Africa, Red Sea included, up to the Pitcairn group, Hawaiian Islands, Polynesia, north to south Japan and south to New Caledonia, Fiji and the Austral Islands. It lives in lagoons and on the outer slopes of coral reefs.

As one of the most dangerous fish in the sea, they will not hesitate to attack if disturbed. They have incredibly sharp teeth which they will plunge deeply into their victim, hanging on for an excruciatingly long time. However, they are not poisonous and the most common cause of harm to humans is when a bite becomes infected. Surprisingly for such a large and intimidating creature, they are actually quite fearful themselves!

Great White Shark

Scientific name: Carcharodon carcharias

Great White Shark
Great white shark off South Africa
Author: Hermanus Backpackers     CC-BY-2.0

Preferring temperate coastal waters where there are abundant fish and other marine mammals, the largest populations are along the California coast, South Africa, Japan and the Farallon Islands. You may have heard that this is but it actually isn’t, it is, however, the largest predatory fish and sits at the top of the food chain unlikely to be attacked by anything other than humans hunting them for sport. 

According to the ISAF, there have been about 350 unprovoked great white shark attacks in the last two centuries, and about 57 were fatal. Great white sharks, which often hunt in very clear water, rely on their incredible vision. There is also some evidence that shark teeth may also function – similar to touch – to help the animals learn more about what they are biting.

Lion Fish

Scientific name: Pterois

Lion Fish
A lion fish
Author: Michael Gabler CC-BY-3.0

Lionfish are fond of coral reefs in the tropical waters of the South Pacific and Indian Oceans. They like the warm marine water, rocky crevices and lagoons. Lionfish are in possession of 18 dorsal, pelvic, and fin spines which are able to produce venom that causes pain, nausea, and even paralysis. Though it’s not generally deadly to humans if you are stung you would be wise to rinse the wound in hot water and seek medical attention immediately. A sting can be extremely painful and lead to swelling, tenderness, warm skin directly surrounding the sting site, redness, sweating, muscle weakness, and a tingling sensation.

Portuguese Man of War

Scientific name: Physalia physalis

Portuguese Man o’ War
A Portuguese Man o’ War
Author: Image courtesy of Islands in the Sea 2002, NOAA/OER.  CC0

This interestingly named fish prefers warmer and tropical waters. but strays can be found up the Eastern Atlantic coast as far north as the Bay of Fundy (Canada). They drift on the currents or use their bladder to ‘sail’ with the wind.  It has numerous venomous microscopic nematocysts which deliver a painful sting powerful enough to kill fish and has been known to occasionally kill humans. This formidable creature resembles a jellyfish but is in fact a siphonophore. 

Although deadly to fish, the Portuguese man ‘o war is rarely fatal for humans. Following a sting, the tentacles leave long, stringy red welts on the skin. There will be local pain, burning, swelling, and redness. The welts last from minutes to hours and a rash may come and go for up to 6 weeks.

Puffer Fish

Scientific name: Tetraodontidae

Puffer Fish
A puffer fish
Author: Brocken Inaglory   CC-BY-SA-3.0

Most puffer fish are found in tropical and subtropical ocean waters, but they have been known to inhabit brackish and even fresh water. Some species of pufferfish are considered vulnerable due to pollution, habitat loss, and overfishing, but most populations are considered stable. 

Almost all pufferfish contain tetrodotoxin, a substance that makes them foul tasting and often lethal to fish. To humans, tetrodotoxin is deadly, up to 1,200 times more poisonous than cyanide. There is enough toxin in one pufferfish to kill 30 adult humans, and there is no known antidote.

Sea Snake

Scientific name: Hydrophiinae

Sea Snake
A sea snake
Author: Phia  CC-BY-2.0

Most sea snakes are restricted to coastal areas of the Indian and western Pacific oceans, although an exception is the Yellow-bellied sea snake  (Pelamis platurus), often found in the open ocean from Africa eastward across the Pacific to the west coast of the Americas. Most other species live mainly in waters less than 30 meters (about 100 feet) deep, as they must dive to the seafloor if they want to acquire food amongst the mangroves and coral reefs. 

It is true that all sea snakes can bite, however, some species’ venom is only potent enough to cause mild to moderate symptoms. These can range from swelling of the bite site to nausea and dizziness. Other species are much more deadly and a bite may result in coma and respiratory collapse. Contrary to popular belief, sea snakes are not aggressive snakes and they would much rather be left alone than have to attack. 


Scientific name: Myliobatoidei

 A stingray at stingray city
Author: Barry Peters CC-BY-2.0

Stingrays enjoy the shallow coastal waters of temperate seas. They generally spend the majority of their time inactive, partially buried in sand, often moving sporadically along with the motion of the tides. They like warm, tropical and subtropical oceans,  freshwaters and lakes all around the world and are known to inhabit the Black and Mediterranean seas. 

Stingrays generally aren’t dangerous — in fact, they are actually renowned for their gentle temperament. They often burrow beneath the sand in the shallows and swim in the open water. Stingrays will usually only sting when disturbed or stepped on by unaware swimmers. It is fairly easy to avoid being stung by a stingray. However, if you’re unlucky enough to experience one you should seek pain relief medicine as soon as possible.


Scientific name: Synanceia verrucosa

Author: Richard Ling CC-BY-2.0

Stonefish are native to tropical waters, from the Indian Ocean to the Pacific. They’re also found in the Red Sea and are a common occurrence among the colourful flora of Australia’s famous Great Barrier Reef. They like to roam among the sea-bed rubble, rock ledges and coral bottoms. If you happen to accidentally step on a stonefish thinking it’s a harmless rock, it will pop up its dorsal spines and release venom from two sacs at the base of each spine. Of course, the more venom that is injected, the worse the consequences will be for you. Stings result in terrible pain, swelling, necrosis (tissue death) and even, on very rare occasions, death.

Tiger Shark

Scientific name: Galeocerdo cuvier

Tiger Shark
A tiger shark from the Bahamas
Author: Albert Kok CC-BY-3.0

The tiger shark, you may have guessed, was named for its striking markings.  The body is grey with dark grey vertical bars or spots on the flanks with a pale or white underside.  Often found in tropical and warm temperate waters. It inhabits both oceanic glasses of water (up to 140 m) as well as shallow coastal waters. They favour turbid coastal areas where freshwater runoff occurs because a wider variety of prey species may congregate to feed in these areas. 

The number of human attacks linked to the tiger shark is about 138, including 36 fatal cases. Most other shark species, stop the attack immediately after they discover it is a human being involved. An example is the great hammerhead that moves on immediately it knows it is dealing with a human and not its regular prey. The sad thing is that there are in fact more tiger sharks killed for their fins than tiger sharks that kill humans. 

Titan Triggerfish

Scientific name: Balistoides viridescens

Titan Triggerfish
A titan triggerfish
Author: Jan Derk public domain

Titan Triggerfish are a familiar sight across the Indo-West Pacific area from South Africa to Southern  Japan and the Southern Great Barrier Reef.  

These interesting and beautiful fish are famous amongst divers for aggressively protecting their surroundings. They will battle with each other frequently, even within their own school. The survival of the fittest is very much the playbook of the triggerfish. They tend to live alone and hunt in the daytime sleeping at night.

It is common for snorkelers and/or divers to be bitten by triggerfish due to their territorial nature. However, the bite isn’t going to be extremely painful or life-threatening. The titan triggerfish is also sometimes known as the ‘moustache triggerfish’ due to the dark line above its lips.