Some beautiful tropical fish with poisonous intentions

Posted in Fish, Nature, Sea, Wildlife on Friday, 6 January 2012

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This edited article about coral reefs originally appeared in Look and Learn issue number 896 published on 24 March 1979.

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Some dangerous fish which live in the coral reef (from top): scorpion fish, file fish and triggerfish by Janet Blakeley

A Coral reef is more than just a stony, if often beautiful, structure built by tiny animals called polyps in tropical oceans. It is also home for thousands of marine creatures who flit in and out of it, and sometimes spend their lives inside it.

These animals turn coral reefs into a naturalist’s paradise, a wonderland where a man could spend his whole life watching just one reef and always learn something new.

Of all the myriads of fish that swim among the reefs, one of the most remarkable is the triggerfish. This has a highly effective built-in weapon which it uses to protect itself against its enemies.

The triggerfish’s weapon is made up of three spikes or spines which lie on the fish’s back, behind the eyes. The front spine, the largest of the three, is fairly thick, and can be erected vertically by the fish. The second spine fits into a groove at the back of the first. The third, the smallest spine, is at the end.

Normally all three spines lie flat along the back of the fish. But when the triggerfish is attacked, they spring into action. The fish darts in a coral crevice, then raises all three spines, with the second spine fitting into the groove of the first and locking it into position.

The triggerfish uses this erect spine to wedge itself firmly into the coral. Its attacker must now break down the coral before it can get at the fish. The spine is locked so tightly that it cannot be pushed down – it will break off before this happens.

The third spine is connected to the second by a membrane. When the danger has passed, the fish pulls down the third spine, which in turn pulls down the front ones. It is this third spine or trigger which gives the fish its name.

Triggerfish may grow to a length of 60 cm. Occasionally, however, a larger fish may manage to get the triggerfish into its mouth despite the spines. When this happens, the triggerfish’s large front spine catches in the predator’s throat and chokes it.

Another fish with a built-in weapon is the surgeonfish, of which there are many varieties. What they all have in common is a frightening scalpel-like spine on each side of the tail. It is this scalpel that gives the fish its name, although in some regions it is called the doctorfish.

Normally the spines or scalpels lie flush with the tail, but if the fish is threatened they are extended on each side of the tail. The fish then fights off its attacker by lashing with its tail, so giving the scalpels a stabbing action. They inflict deep, jagged wounds.

The surgeonfish is especially dangerous once it has been caught. Many an unwary fisherman has had his hand lacerated by the fish. Most of the 100 species of surgeonfish reach a length of at least 50 cm, which makes them creatures to be treated with caution.

One fish which gets on very well with the surgeonfish, however, is the bluehead. This little fish swims about in large shoals, darting in and out of the coral. The bluehead gets its name from the colour of the male’s head, which is separated from the body by a white collar. The body itself is yellow or yellow-green.

Young blueheads can often be seen clinging to the body of certain kinds of surgeonfish as they swim along. It looks as though they are just hitching a ride, but in fact the blueheads are performing a very valuable service to the surgeonfish. By eating the minute organisms on the surgeon’s body, they perform an important cleaning function.

Blueheads are extremely curious. If they see a skin-diver, the whole shoal will often surround him, all struggling to have a look at him through his face-mask.

Another strange inhabitant of the coral reefs is the filefish. It acquired this unusual name after years of use by the South Sea Islanders. When one of them wanted to smooth a piece of wood, he went to his coral reef and caught himself a file-fish. The flat-shaped fish has a hard and very rough skin. When the skin was dried, it was used as a coarse sandpaper.

Filefish, which are related to the triggerfish, grow to a length of 60 cm, and are often a mottled black, orange and yellow in colour. They feed mainly on plants, which they nip off with their exceedingly sharp teeth.

Quite apart from the shark family, about which much has been written, there are many creatures in the reefs which spell danger to man as well as to their fellow fish. Among these is the jewfish, a giant member of the grouper family, which can attain a weight of 400 kilograms.

Jewfish are solitary creatures, and, when not swimming in a dignified fashion near the bottom of the water, they often lurk in coral caves or under rocks. Many skin-divers consider them more dangerous even than sharks, for they have the disconcerting habit of suddenly charging intruders, often without warning.

They eat enormous quantities of fish of all kinds, which they catch while lying in wait with their mouths open. Once a fish is drawn into its huge mouth, backward-pointing teeth ensure that there is no escape.

One creature which all divers try to avoid is the colourful scorpion fish. It looks beautiful, but its body is covered with long, projecting spines.

Scorpion fish keep close to the bottom of the water, often lurking in crevices and caves in the coral. But each of the spines is like a hypodermic needle, and can inject a powerful poison into anything which touches it.

Many a bare-footed diver has unwittingly trodden on one, and the fish’s venom can spell death unless the diver quickly leaves the water. Some species of scorpion fish are particularly deadly. Among these are the turkeyfish, which has even been known to attack a victim, repeatedly stabbing it with its spines.

Most dangerous of all is the stonefish, found in the Indian Ocean. It looks, as its name suggests, just like a stone, but the careless swimmer stepping on it finds that the pressure of his foot causes venom glands to inject a neurotoxic venom into him. Death often follows, even to humans.

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