A lot of fish view puffers as either easily bullied (they can be) or a threat (rightfully so) and attack them, especially cichlids. I've tried mine with guppies with mixed results. He killed the first few I tried when he was real small. When I moved him he left them alone for a long time but recently I've seen the population start to dwindle. This time though they are gone not just killed. Fahakas have a bad reputation for being killers. If you value any other fish you'd thought of putting with him I'd not do it. You also need to worry about the other fish picking on him or bullying him off of his intended food. That's a small chance but that is what has happened with my buddies. He has his in with an African cichlid of some sort, not from the lakes it's black with white and blue speckles. I forget the name. It has to have the first go at any food in the tank. I think sooner or later though the fahaka will kill it.
Mine is pellet trained and seems to like most pellets. I got lucky as long as the pellets keep his teeth trimmed, so far so good. I do feed him snails from time to time and I have a ton of empty snail shells from my breeding colony that crashed. He happily crunches those up. I've tried clams no luck unless it's a half shell but then he doesn't go after the shell. He'll eat crayfish also. I had a ton of them but then they stopped breeding. I think the big male killed all the females. I have a hard time telling them apart.