Scaredy-Fish?

Piranhas are evil, soulless, bloodthirsty critters who would rather bite your leg off than look at you, right?

Of course they are!

But researchers are turning up something else about them. They may also be . . . scared.

It’s been thought that piranhas school together in hunting packs, the way wolves do, but it turns out that they may just be running in schools because they’re chicken, some scientists have determined.

EXCERPT:

"We started off with the premise that they school as a
means of cooperative hunting," she said. If that were the case, the
researchers would have expected to find certain fish associating with
others, as the principle of reciprocal altruism — I scratch your back,
you scratch mine — would be in play. "But there was very little
evidence that the same fish stayed together over time."

They also found that piranhas apparently are so anxiety-prone that they start hyperventilating if put in a tank where they can see humans around them or during a simulated attack by a piranha-predator:

The
researchers also knew that piranhas were prey for other animals,
including cormorants, dolphins and caimans. In their studies, they
noticed that breathing rate, a measure of stress, increased when the
fish were put in a tank, as if they were afraid of being attacked.

The
researchers experimented by placing the fish in tanks in groups of two
to eight. As reported in the journal Biology Letters, they found that
breathing rate increased with smaller schools. Another experiment
simulated an attack by a cormorant and found that although all the
piranhas breathed faster in response, those in larger schools returned
to normal sooner. The fish found safety in numbers.

Conclusion?

"We thought it would be quite neat to do work on
piranhas because so little is known about them," Magurran said. "But
this notion that they were fearsome fish, frightened of nothing — we
had to revise that.

"They’re basically like regular fish," she added. "With large teeth."

GET THE FIRST STORY.

But wait, there’s more!

Another article on the same group of researchers notes (EXCERPTS):

Professor Anne Magurran even had to put up screens round a fish tank
used to study wild Amazonian piranhas because they were so scared of
seeing humans close by that they began to hyperventilate.

"Mostly, they were terrified of us. If you put them in an open tank and
just watch them, their gills would move very quickly – like someone
hyperventilating through stress – so we would screen them off so we
could observe them without frightening them," Prof Magurran said.

Personally, my response would be: "Good! Let them be scared! In fact, let’s put them all in tanks and dance around them wearing scary masks and brandishing spears and long, sharp-pointed knives." But apparently deliberately inducing terror in the piranhas would count as "interfering with the test subjects" and thus would be "bad science"–however much the piranhas might deserve it.

Apparently not all piranhas are as evil as others, though. Some are even vegetarians:

Piranhas’ diet is far less spectacular than might be popularly
imagined. They eat invertebrates of most types, waterfleas, crabs,
shrimps, small fish and vegetable material. "When the forest floods,
the water rises up into the trees and the fish swim among the
branches," Prof Magurran said. "Fruit from the trees is moved about by
the water and virtually all the fish eat it.

"There are different species of piranha [other than the red-bellied
kind] that are actually vegetarian. Some of them have extremely robust
teeth and large jaws, but they just eat fruits."

It also seems that, despite their best efforts, our enemies the piranhas have not succeeded in actually killing one of our kind (so far as can be verified), though they have tried to attack us when we’ve interfered with the nesting sites where they spawn more of their evil breed of mankind-enemies:

There have been no confirmed cases of humans being killed by
piranhas, although there was an incident when people swimming near a
dam in southern Brazil came under attack.

"What happened was they were disrupting the piranhas’ reproduction.
Piranhas build little nests, so they weren’t too happy," Prof Magurran
said.

"But the idea of a cow walking across a stream and being reduced to
a skeleton halfway across is exaggerated. They don’t tend to attack
live prey in normal circumstances."

A human walking into a stream filled with piranhas would almost
certainly emerge unscathed. Prof Magurran said: "They’d want to get
away from you, probably. You can swim in areas where there are
piranhas, although there are times of the year when you wouldn’t want
to do that, when they are very stressed or very hungry.

"You wouldn’t want to disturb them too much or threaten them because
they would bite. But they are just ordinary fish, really – ordinary
fish with sharp teeth."

Which only means that regular fish are also
evil, soulless, bloodthirsty critters that would rather bite your leg
off than look at you–they just don’t have the teeth to do it.

GET THE SECOND STORY.