Thats very cool. I have mine in black rocks and they have turned dark i was suprised that that early they turned colors. what have you fed them so far. mine have been eating shrimp twice a day. And hitting the food hard. And they like chicild food.
I know you will enjoy.
They are 2-2.75in. I just got them saturday. I been feeding them beefheart in the morning and chickheart at night. I need to get some shrimp and krill. I'm impressed with these guys, they are not skittish like the caribe I had at the same size. And they have the same ferocity in eating like the caribe but don't have the appetite. My caribe at the same size would eat double what I feed the pirayas. I'm completely satisfied.