I bought seven 2"-ers. One was eating the most and grew the fastest. He ate two of his brothers when he was perhaps around 5"-7", I suspect. Never had a problem with many others of great various sizes in a large pond. In a small tank - anything's possible. One of my other 2"-ers decimated a bunch of african clawed frogs in a 30 gal. Grew real fast as a result but the wife was unhappy. Frogs were her faves.