Notorious killers

Blood in the water is said to whip a shoal of piranhas into a demonic feeding frenzy, and although the smell of blood or body fluids makes them more likely to bite, it is the sight of the prey that triggers the attack, writes Nutan Shukla

STORIES of shoals of predatory piranha attacking and devouring humans are more the stuff of legend than of truth. However, these small fish, found in Amazonian rivers, certainly have the potential for such devastating attacks. Their schools have been observed to skeletonise a 180- kg pig within minutes.

Many fish have deadly teeth, but those of the piranha have become the stuff of nightmares. Of the 20 or more species, four are recognised as notorious killers. They have a mouth filled with razor-sharp, triangular teeth designed to slice off bite-sized pieces of flesh. A shoal, which can number hundreds if not thousands of individuals, can reduce a large capybara to a skeleton in less than 2 minutes. The fish pick the bones clean. There is a classic description of a piranha attack by William Innes, the doyen of home aquarium keepers. He wrote of a pig being dipped into a piranha-infested river and ‘each time it was lifted out of the water, it was reduced in size.’

Blood in the water is said to whip a shoal of piranhas into a demonic feeding frenzy, and although the smell of blood or body fluids make them more likely to bite, it is the sight of the prey that triggers the attack. Piranhas only attack fish which are four times as long as they are wide. Fortunately for their shoal-mates, piranhas themselves are less than three times as long as they are wide.

Vying with the piranhas for the title of the ‘world’s most ferocious living fish’ must be the blue fish of the Atlantic coast of the USA. It has been described as the ultimate ‘animated chopping machine’. A shoal, working together, will tear into their prey, often fish little smaller than themselves, leaving a trail of blood, flesh fragments and pieces of entrails in their wake.

In the deep sea, small, 1-2ft-long dogfish form into roaming underwater packs. Luminous light-emitting organs along the body enable pack members to keep together in the dark of the abyss. They hunt together taking squid larger than themselves. Like angry wasps, it is thought that they swarm all over the prey, anchoring themselves with their pointed top row of teeth and slicing off chunks of flesh with the razor-sharp lower band of teeth.

Dogfish are members of the shark order and there are about 70 species. They are found in the Atlantic Ocean and along the Pacific coast of North America. They have long, slender bodies, large fins and a long tail. Most are less than two metres long, but the largest dogfish, the greenland shark, can grow as long as six metres. Most of these fish are carnivorous and eat small fish and other sea animals.

One species, the lesser spotted dogfish, is the most common. It is often found on sand banks where it hunts small fish, molluscs and crustaceans, mostly at night. It grows up to 1 metre and is covered by brown spots. It is also known as the rock salmon or rough hound.

But perhaps the most appealing story of undersea co-operation comes from Australia. There, on the coral reefs of the Great Barrier Reef, a small, brightly coloured, petal-like, pink, white and blue gnathopyllid shrimp attacks starfish, including the infamous crown-of -thorns, which is out of control and gobbling huge sections of the vulnerable reef system. Male-female pairs of shrimps work together and tickle the starfish’s feet, which causes the spiny star to loosen its hold on the coral. Gradually, they turn it over. Once it is upside down, the shrimps feast on the soft underside before the unfortunate starfish can straighten itself.