Will a trigger the same size as other fish eat them. I was told at the store they were not aggressive and now online I'm seeing something different! Help! he's acting fine now
Depends on a lot of factors - a trigger won't eat fish the same size but may kill them depending on the species of trigger, tankmates, size of tank, etc.
Picasso can be aggressive, but will probably be fine with your additions but the 20 gallon tank is too small even for a tiny juvenile Picasso -- the lack of side to side swimming room will stress him out and could lead to significantly more aggression..
Any lfs that sold you a picasso knowing he was going in a 20g, should not be in business. Not only is it just not right to put a fish like that in such a small tank, even a 1" picasso could possibly shred the rest of your tank; and picasso's aren't even top teir aggressive triggers.
I had a Picasso for 10 years in a 75 gallon and his best friend was a blue damsel but he would eat any other damsels I added.
He was my favorite fish I've ever owned he was incredibly smart and would play with toys and I even taught him tricks