02 July 2007

Piranhas not so fearsome?


Conservationists working in Brazil have uncovered evidence that indicates that the red bellied piranha may not warrant its grisly image. A team led by Anne Magurran at the University of St Andrews studied the fish in their natural habitat and in large tanks at the Mamiraua Sustainable Development Institute in Brazil. Their observations of piranha shoals suggest the fish may have a nervous disposition and huddle into shoals out of constant fear of being eaten by other predators.

In the Amazon, when water levels are shallow, the fish are more easily picked off by large predators including river dolphins, caymans (a relative of the crocodile) and big fish such as the pirarucu. Piranhas formed large shoals, gaining safety in numbers. Although larger shoals are easier to spot, predators find it harder to pick off a single fish because of the 'confusion effect', caused by the erratic movements of the shoal. Using giant water tanks and models of birds of prey, the team simulated airborne attacks on different shoal sizes.

They found piranhas in smaller shoals were more distressed and took longer to calm down. The nervousness was monitored by observing a structure near the gills which quivers rapidly with stress. "Our study has given us a better understanding of the function of shoaling. Previously, it was thought piranhas shoaled as it enabled them to form a cooperative hunting group. However, we have found it is primarily a defensive behaviour," said Professor Magurran.


Hmm, they’ll be drummed out of the predator club for this sort of timidity, I'm sure!

7 comments:

Anonymous said...

Next they'll be telling us that piranhas are vegetarians!

jams o donnell said...

Why not? They are obviously kind to their mums too!

frolix22 said...

Those James Bond-style films have a lot to answer for! Poor, misunderstood fish.

Steve Bates said...

"Next they'll be telling us that piranhas are vegetarians!" - roger b.

Maybe they only eat vegetarians...

beakerkin said...

Roger

The fish commonly known as piranhas comprise many species and a few are vegeterian.

Jams

In many states including NY it is illegal to own a piranhas. However, as far as being dangerous your average goldfish is more dangerous to the environment in New York.

Piranhas that are placed in lakes die in winter. Goldfish make a mess of the lakes.

Then again there is much that we do not know. Those turtles in your park in the UK are allegedly not able to hibernate. Apparently someone did not tell the turtles.
Despite what experts said they may be able to reproduce.

In actuality the local natives fear the fresh water stingray more than the piranha.

elasticwaistbandlady said...

They'll have to do a remake of the 80's cheese fest movie,'Piranha,' and switch it out for a kinder, gentler piranha that only wants to be listened to and hugged.

jams o donnell said...

Beakerkin, Roger is a naturalist and probably almost certainly does realise that the piranha comes in more than one style. The post and the comments were meant to be tongue in cheek.

Ewbl, perhaps it could be a friendly feel good film featuring a variety of grilled tofu dishes (not bad in themselves!)