The vast freshwater ecosystem of the Amazon River is home to abundant animal life, and many of its species thrive by virtue of their ferocity. If one were to ask the locals which of the river's indigenous species is the most treacherous, a few might describe the roaming packs of carnivorous piranhas, or the massive anaconda snakes; but based on the general sentiment of the region, the most frequently uttered response would be "candirú." The candirú is a tiny catfish which dwells in the depths of the Amazon River. These fish do not hunt in packs like the piranha, nor...