More than any other fishes - including piranhas - freshwater stingrays are feared by people who live along the Amazon and its tributaries. Stingrays bury themselves in the sand or mud bottoms of river shallows. Anyone who accidently steps on one stands a good chance of being lashed with the sharp, serrated spiine that grows out of the stingray's tail. The spine carries painful venom attacks the nervous system and heart.

These stingrays' nearest relatives live in the Pacific Ocean. Their ancestors were marine stingrays that lived in a seaway that connected with the Amazon River east of the Andes. Some would have been trapped in teh river's estuary as sedimentation closed the connection. Adaptations to a freshwater habitat included a change in the salt concentrations in their bodies.

Amazon Rising: Seasons of the River. Shedd Aquarium