h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Oh dear, myths abound... and many about this much over-rated "terror" of South American tropical rivers. About 13 species of piranha swim among murky waters of shaded sluggish streams, yet only one or two are at all dangerous. Most feared is the red-bellied piranha, also one of the smaller species. This is the one normally associated with flesh-stripping abilities so beloved of Hollywood B-movie directors. Yet you can take a swim in "piranha-infested waters" with nary a nibble. Only the presence of open wounds, or blood, initiates an attack. Then indeed, their teeth - sharp and serrated, triangular like those of a miniature shark - will tear and pluck at the prey. But most piranha in fact serve in less gory roles. The white-bellied piranha is much larger than the red-bellied, but specializes on fish, so you need bait comprised of fish to catch this species... (to be continued).

There was a good documentary on the red-bellied piranha fish on UK terrestrial TV a while ago; they also tend to get a bit fidgety when the water levels drop and they're concentrated in small pools...

But my, they *are* ugly

Azimuth