This is the notorious Red-Bellied Piranha (Pygocentrus Natteriri) of the Amazon river system. These are reputedly the most ferocious of the Piranha species – the one mythologized in the horror movies. It’s a shame the image can’t show the rows of razor-sharp saw teeth in those jaws. Although these fish live in large schools, they apparently rarely attack large living animals, preferring to scavenge instead. They grow to 33 cm in length; this one’s about 2/3 of that size and is safely contained in an aquarium!