If you pm me your email, I could send you "Environment-related life-history trait variations of the red-bellied piranha Pygocentrus nattereri in two river basins of the Bolivian Amazon"
It's a bit sciency- I'm not sure how in depth info you want but it has chapters on information on sex ratio, breeding seasons, size and age at maturity, fecundity and oocyte size, age and growth amongst others. It sounds like a pretty comprehensive study (although from only 2 river basins)- might be useful?