There are a number of dangerous sea creatures. Many have the capacity to severely injure or even kill people. But they very rarely attack for no reason. Common sense is the best way to avoid an attack.

Sharks really don't deserve their reputation as killers. More people are killed each year by bees or even lightning than by sharks. Of all the known sharks, 80% are harmless to humans. There are many reasons why a shark may attack humans: it may mistake them for its normal food; it may be just curious; the human may be seen as a threat to the shark's territory; or it could even be mating season.

When a shark does attack, even if it is just 'testing', the results can range from minor cuts and gashes to severe, or fatal, results. But even then, you can be lucky - for example, 75% of great white shark attacks are not fatal! Sharks generally attack in inshore waters, near deep channels or where rivers empty into the sea. This is because these areas are where they expect to find their 'normal' food. The best defence is to never swim alone, or in areas where dangerous sharks are known to be found.

This is by far the most poisonous fish in the world. It is particularly dangerous to people because, lying on the ocean floor, it looks just like a rock - or a stone. It normally feeds on small fish and shrimps, which it waits for on the bottom (as still as a stone) - and then sucks into its mouth with lightning speed.

However, because the Stonefish is also food to other animals, it has developed a row of 13 poisonous spines down its back as a defence mechanism. Each spine is surrounded by a sheath, which holds the poison glands. When an unlucky human steps on a Stonefish, the spine penetrates the foot, the sheath is pushed back and the poison glands squeezed until they shoot their venom along grooves in the spine - deep inside the victim.

The pain is unbelievable and may last for hours! What's worse is that, in some cases, the victim can be temporarily paralysed - or even die from the poison! Medical help is absolutely essential.

Thick-soled shoes may help - but the spines can penetrate even  those if jumped on. And be v-e-r-y careful about picking up or turning over anything that 'looks like a stone'!

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Stingrays have a long, barbed tail, like a hard 'whip'. When in danger, a stingray will lash out with this tail with great force. This can cause serious cuts, even requiring stitches. Stingray spines have been known to go straight through wetsuits and even shoes - so beware! As well as this, many stingrays are also poisonous.

People wading are most likely to be affected - although the stingray doesn't actually 'attack', it will lash out if frightened or if it feels trapped. If you shuffle your feet, splash and make plenty of noise, most stingrays will quietly disappear long before you get there. If you are gashed, seek medical help, because small bits of the barb may actually break off inside the wound.

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The sea wasp IS deadly! This large jellyfish is shaped like a bell, with 16 tentacles up to three metres long. These tentacles are absolutely covered with stinging capsules. Their deadly poison is 'shot' into the victim. Normally, this venom is used for capturing the sea wasp's prey, such as prawns.

The sea wasp can kill a human within minutes. The first symptom is agonising pain, followed by huge 'welts' on the skin, like purple or brown bruises. If not treated, the poison causes death by shocking the heart and stopping breathing. There is an antidote to the poison, but it has to be given with minutes if it is to be effective.

The only sure method of avoiding being stung is to stay out of the water where sea wasps are known to live. If anyone is stung, trained help must be sought immediately.

There are a number of poisonous fish but, unlike the Stonefish, these fish are more active and will always try to get out of your way.  Even some aquarium fish, such as the lion fish, butterfly cod and fire fish, come under this category!

Then there's the catfish, which has three spines - with barbs - which stick out from its back and side fins. These shouldn't be confused with its 'whiskers', which are harmless.

Stings from any of these fish can be very painful - or even fatal. And even if the fish are dead, the poison will stay 'alive' for days, so take care if you pick one up!

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The cone shell is a mollusc, a member of the same family as snails. It is usually found close inshore in sandy areas under rocks. Because it is quite attractive, it is sometimes picked up by people who don't understand the danger.

The cone shell has a poison barb (made up of specially modified teeth), which it 'fires' into its prey to capture it and eat it. The poison is very strong - strong enough to kill a full grown human. If stung, symptoms include extreme pain, nausea, weakness and perhaps even paralysis of the breathing muscles. It is essential to seek urgent medical attention.

The safest course of action is to NEVER pick up a shell, or put your hands or feet under rocks or where you can't see them.

You can SEE that a sea urchin is covered in long black spines - so stay away from them! They are sharp, and can penetrate deeply into your body. Quite often, they will break off inside the wound and need to be removed by a doctor, or else the wound will become infected and stay that way for a long time.

However, experts are still arguing about whether the sea urchin actually injects poison into its victim or not.

There is a far more dangerous urchin, responsible for several deaths in Japan, called the 'flower urchin'. It looks like it is  covered in flowers, but they are really vicious little 'pincers', which inject poison into their victim. This one can kill!

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While this creature has sharp spines, they are not what does the real damage. Each spine is covered by a thin layer of poisonous skin. When a spine penetrates your flesh, the poisonous skin is pushed into the wound, causing pain, vomiting and swelling.

Just like the sea urchin, the actual spine may also break off inside the wound and need medical help to remove it.

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Although hydroids look like plants (and are even called 'fireweed'), they are actually colonies of small animals. Each of these has many strong stingers, called 'nematocysts'. They use these to capture their food and to defend themselves. Some hydroids have very powerful stings, which can cause severe pain (for up to a week) as well as swelling.

Hydroids are found in shallow reef areas, and sometimes are seen growing on jetty pilings. It is easy for a diver to brush against one - with painful results.


These, again, aren't really single animals, but colonies of small animals related to the hydroids. The difference is that they have a hard, external 'skeleton'. There are different types of stinging corals; some look like large sheets, while others may have 'antlers' and be a yellow-green or even brown colour. The effects of their stings are very similar to the hydroids.

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The blue-ringed octopus is much smaller than everyone thinks. Even the largest are only 20 centimetres across their spread tentacles at most. It is not a naturally aggressive creature, but will bite if it is disturbed or frightened. Its colour also changes from its normal yellow-brown, and its blue rings become very bright.

The poison is not injected into the wound, but carried in the octopus' saliva. When it bites with its 'beak', the poison is washed into the wound. Actually, it has two different poisons. One is almost harmless to people, but deadly on crabs, which is the octopus' main food. The other is probably used as protection, and is deadly!


The bite is small, and people may not even know they've been bitten at all. The first symptom will be numbness around the mouth. This is followed quickly by paralysis. If medical attention is not immediately sought, people can die as their breathing muscles are paralysed!

The blue-ringed octopus is usually found in small rock pools and cracks in the rock - even in discarded drink cans and bottles. NEVER put your hands inside anything where you can't see. If bitten, wash the wound with plenty of water, to wash off as much poison as possible - and get medical help immediately.

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Many sea snakes, like sharks, have a bad reputation they don't really deserve. Although their poison is stronger than land snakes, they are actually quite shy and prefer to stay well away from people. They will usually only bite if severely provoked - and even then they may not use their poison! Their venom isn't meant for defending themselves, but for killing their food quickly to stop it escaping.

However, this doesn't mean you can go and play with sea snakes! The best rule is to leave them alone.

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Morays, with their gaping mouth full of needle-sharp teeth, are frightening to look at, but are not naturally aggressive towards people.

However, divers have been 'attacked' by morays, and their sharp teeth have caused considerable damage. Part of this can be blamed on the foolish habit some divers have of feeding morays by hand. After a while, the morays expect the food, and can approach divers on sight and bite their hand - because they believe there is food there!

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Some fish have poisons in their own flesh, that do not affect them, but will poison anyone who eats them. These include the toad fish, the puffer fish, porcupine fish, box fish and sun fish. Many of them are famous for their ability to puff themselves up with air or water like a balloon. But they are also famous for their poison flesh, which has the same venom as the blue-ringed octopus!

Although it is very easy to catch these fish on a fishing line, they must NEVER be eaten, as they can easily be fatal.

There is a special form of food poisoning which sometimes happens in coral reef fish. This is called ciguatera. It occurs when plant-eating fish eat a tiny animal growing on certain seaweeds. This organism has the poison. These fish are then eaten by flesh-eaters, such as mackerel or coral trout, and the poison builds up in their bodies. It doesn't affect the fish, but it definitely does affect anyone who eats them! To make matters worse, the poison has no taste or smell - and cooking the fish doesn't destroy it. Though usually not a deadly poison, it can make people very sick and has been known to be fatal.


Large reef fish (over 10 kg) are most likely to be affected. Symptoms usually begin 2-12 hours after the fish are eaten and can include breathing difficulty, perhaps requiring CPR. If symptoms develop, try getting the patient to vomit while you seek urgent medical attention.

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Toad/puffer fish don't have scales. They have a mouth not unlike a 'beak', and can chomp cleanly through a toe or finger! (As well as being poisonous to eat!)

If eaten, a puffer fish can kill you within 17 minutes! A blue-ringed octopus can kill you in 30 minutes - and a box jellyfish ('sea wasp') has been known to kill within three minutes!

The surgeon fish has razor-like blades at the base of its tail - and can cause nasty gashes.

In the last hundred years, at least 65 people have been killed by box jellyfish.

Most sea anemones are harmless - but a few do have a very strong poison that can cause severe effects.

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