I was hanging out in Puyo with a local friend, and we came across some people selling these "carachama" fish that they had caught from the river that day. They told us that they dive down, pull them off the rocks, and swim back up with one in each hand and one between their teeth.
It was a fantastically prehistoric looking fish, a type of Loricariid catfish. The scales were hard, like a lobster (it was a challenge to break into!), and the meat was very tough and chewy.