To my eyes the finage and scale pattern looks more krobia the aequidens. I'm ready to be wrong but I think it's krobia guianensis.
It's not unusual for some fish to exceed average size.
Jason - there are several species in the genus krobia, not just xinguensis. I've kept and bred guianensis, and this is exactly what mine looked like. I lost my male a while back, but still have the female.