Arawana, Goby and the Clownknife are all big boys. I've never see the Arawana chase after anyone, other than feeders and even then there wasnt a heavy effort. The clowknife sometimes gags on large feeders so I doubt it's him. The goby hides out 24/7. I've never actually seen him eat, and that's probably because he's eating his tankmates (or at least those he can fit in his mouth).