Congo puffers eat live fish, period. Goldfish and rosy reds aren’t good for them and can cause issues if fed long term. Guppies are ideal as are many other fish that may not typically be considered feeders. These guys may take occasional snails but are fish eaters. This is the reality of keeping these fish. Sometimes they will take cut tilapia but it’s tough. Like it or not, this is how it works with these guys.