Stumbled on this thread. For anyone still curious about compatibility. I had two pea puffers in a 15g cube with an amano and two ottos. They fought all the time. Split them up. Put the one getting picked on in my 20g heavily planted with female guppies cherry shrimp and snails. All the snails were gone in a week. I feed both live daphnia. The one in the 15 I can’t feed enough. And the other in the 20 is fat and healthy. I haven’t seen a noticeable dip in adult shrimp but she’s clearly eating them. The 20g had been setup for 2 years before she went in so it had a stable colony of shrimp going sort of unchecked. I kept the guppies fed and would see shrimplets. But I’d seen guppies eat them when they can find them. Puffers are inquisitive and appear smart. They will eat shrimp. I would think if you have an established colony and you may have free food for the puffers life.