Your fish is a Charax gibbosus (or a very similar Charax sp.), commonly called the glass headstander in the U.S. They are very sturdy, carnivorous South American characins. I've kept a few over the years; the last one I had became quite aggressive (fin-nipping and scale-biting) and I gave him away to a LFS. I had another one many years prior and it was completely peaceful (go figure) and it lived for many years. They have pretty good-sized teeth, from what I recall.
Although called "headstanders," they are quite different from the marble headstanders (Abramites) and spotted headstanders (Chilodus) which tend to eat a lot of vegetation. Typical S.A. "tetra" water conditions; temp in the mid-70s, but will tolerate higher temps, prefers acidic water but can adapt to slightly alkaline. Don't keep with small fish or thread-finned fish. I believe they get about 4"-5" long. I would think they'd be fine with semi-peaceful cichlids (firemouths, uarus, severums), other sturdy characins (silver dollars, anostomus, chalceus), all sorts of South Anerican catfish, etc.