Great appetite
Yes, but they will always have some skitted trait to some degree. I'd say once your Piraya reaches 9" it won't hide/dart much at all. Needs to get used to it's surroundings. Each fish has their own temperament and personality, of course.
My Rhom is ~7.25", thinks he's a badass most of the time trying to chase me and my wife away from his tank, but when we're wearing dark gray/black clothes, he acts like he just saw the boogieman
releases a little ammonia wetting his pants, and darts around like crazy.