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Piranhas: shy, easily startled and conservative

Brigitte Osterath
May 23, 2016

Do you think piranhas are bloodthirsty monsters, who skeletonize any creature they can eat within seconds? Then you will be surprised! DW's Brigitte Osterath has come to know seven piranhas quite intimately.

red-bellied piranhas Photo: Rainer Dückerhoff
Image: Rainer Dückerhoff

Ever since I started keeping piranhas as pets, people have asked this one question over and over again: 'What happens if you reach into the tank with your hand?'

Most people seem to assume that doing this would end in a bloodshed.

Piranhas, they think, will rush to rip off pieces of flesh from my hand and arm within seconds, leaving only gnawed-off bones.

The reality, though, is much more boring.

When I put my hand into my piranha tank, the fish swim away. They are terribly scared of human hands - at best, they are not interested at all.

But I have to admit that I, too, had to find this out for myself.

red-bellied piranha Photo: Rainer Dückerhoff
Sparkling scales and a prominent underbite are characteristic features of a piranhaImage: Rainer Dückerhoff

Seven red bellies as housemates

In January this year, I happened to get unusual pets: seven Pygocentrus nattereri, also known as red-bellied piranha.

That's right - these are the predatory fish with the sharp teeth that forage in the Amazon River in South America. Hundreds of these creatures cluster together in schools looking for food.

Piranhas have a reputation for being ferocious and always hungry. The fish are rumoured to be able to rip apart cows - and even humans - while their victims are still alive.

In 1821, naturalist and explorer Alexander von Humboldt described the black spot piranha, Pygocentrus cariba. The species would attack people swimming or bathing in the river and bite off considerably big pieces of flesh, von Humboldt wrote.

And yes, the lurid tales have an element of truth. Piranhas can get very dangerous - when they are hungry.

red-bellied piranha Photo: Rainer Dückerhoff
Piranhas are only dangerous when extremely hungryImage: Rainer Dückerhoff

Human flesh in times of need

During dry seasons, tributaries of the Amazon River can run shallow. As a result, a school of piranhas may get trapped in small water pools without any connection to the river.

Quite soon the predatory fish will have eaten up everything creeping or swimming in the small pool of water. Then they get hungry.

After weeks or even months trapped this way, they will lose their shyness and attack anything that falls into their watery prison. Even cows and humans can fall victim to the piranhas.

People who live near rivers with piranhas know which waters they should avoid.

But you can also see children playing in rivers with piranhas - where the fish have enough to eat and are not desperately hungry.

Piranhas prefer to eat other fish, crabs and invertebrates over human flesh.

Better safe than sorry

It took me three months to get up the nerve to reach into my piranha tank bare-handed, without any protection.

Now, I am no longer scared when I maintain and clean the tank, rearranging plants or removing excrement, for example.

This doesn't mean I allow myself to be careless.

A piranha who is startled or feels threatened will bite his way into a human hand. And judging by their very sharp teeth, I imagine it would hurt an awful lot.

Scared of the unknown

Piranhas are very conservative. They don't like change - including when it comes to food.

In the wild, they are the Amazon's health police. They eat sick or injured fish, and as such, prevent illnesses from spreading. They are not gourmet diners.

My piranhas are quite picky, though, as I found out.

In the tank, piranhas only eat what they clearly recognize as food - that is, what they have been fed before. If you regularly serve them large pieces of trout, that is all they will want to eat.

It took me more than two months to get my piranhas accustomed to eating cooked prawns and dead smelts from the pet shop. Their previous owner had not fed them prawns and smelts, so to begin with they refused to eat them.

They don't appreciate change in the tank either, be it new plants, roots or stones.

Piranhas are most satisfied when everything stays as it is.

Schools make them happy

Piranhas are very robust and practically never get sick - at least, this is what books on the subject will tell you.

The predatory fish are, however, prone to suffer from stress. Too much light, bright gravel, too much noise or hubbub around the tank will drive them crazy.

Plus, they like plenty of hiding places for when life gets too exciting around them.

red-bellied piranha Photo: Rainer Dückerhoff
Is that a smile? Piranhas are often scared, and sometimes curiousImage: Rainer Dückerhoff

In the rare moments when my piranhas are not scared they seem to be quite curious. When I want to take photos of them and hold my smartphone up the glass of the tank, they swim to see what is going on.

They are at ease when accompanied by other piranhas. In a school, they feel the most secure and happiest.

But it's not all perfect harmony. My piranhas do quarrel and fight with one another on a regular basis. The sound can be terrifying.

In the heat of a battle, they can bite off bits off each other's fins. Luckily, the fins grow back quite quickly.

Big personalities

There is one other question I get asked over and over again: 'Can you tell them apart?'

Brigitte Osterath and a piranha in Stuttgart's zoo Photo: Magnus Heier
DW's Brigitte Osterath clearly adores piranhasImage: Magnus Heier

The answer is: yes, of course.

My piranhas are not only different in size, but each one of them has characteristic features - such as a prominent chin, a cloudy eye or a belly that is redder than average.

So piranhas are no different from almost any other animal species.

In captivity, piranhas can live to be up to 30 years old - older than dogs.

My piranhas all have names: Seamus, Hannibal, Hector, Carlos, Vito, Piet and El Niño.

Piranhas are real characters. And that's why I love mine so much.