Have any of yours had babies yet ?
Most of my experience with them in my own colony teaches me they are rather docile if timid. Until they have babies. At which point the majority of the females become related to piranhas.
Not every one does it. And they don't always draw blood. One of my big girls got me last night for messing with her babies. She bit me, do not mistake that, but it was a warning bite. She didn't even leave a red spot. She just wanted me to leave her babies alone.
However, I have females who will happily amputate a finger in defense of their offspring if I let them.
Gale