So what do you think the most feared fish in the world is? Great White? Piranha? Sting Ray? Ha! Those are all teddy bears compared to the candiru.
So the common story goes that this small Amazonian catfish will swim up the urinary tract of a swimmer who decides to pee in the river. The catfish wiggles its way in and then opens up it three sharp spines and holds fast where it will start eating its victim from the inside out. Ouch!
Here is a video from the BBC on it. http://youtu.be/QQWgUht-ObI
Also the fish scored a segment on Animal Planet's River Monsters.