its not acestro. Its Brycon dentex. Some people DO call them Red Tail Barracudas... just another common name, which obviously could create confusion. I have 4 of them. Mean as HELL. Scale eaters, at least to a certain extent. They will harrass and attack fish much larger than they are (my 3" one will dive-bomb my 10" ATF). ITs not that they will tear something up right away, they just pick it to death. They are nasty fish. But, for the most part, they are most agressive to each other... they constantly harrass each other. Non-stop violence, but nothing to dangerous. Just some knicks, scratches and cuts constantly.
Some people have said these are Oligosarcus spp. They are not. For one we know for a fact they get over 12"... in fact I know a person who had one over 14". SEcondly, color is not quite right. Finally, they are collected in Ecuador (mine were at least) and Oligosarcus are found much farther South and East... not in Ecuador. Brycon dentex are from Ecuador region.
They chew things up... like their food in pieces (like chunks of shrimp, chunks of fish, pellets). They do not swallow fish whole like acestrorhyncus. THeir teeth, though defnitely visible and used, are not as prominant as an acestro. They kind of have the character and attitude of mini-dorados.
NICE FISH. Enjoy it. Get a few more.