A compressiceps will kill fish up to about an inch long, even though it can't swallow them ... it will crush the head and slurp out the goodies ... watched this happen to tetras I knew were way to big to swallow. :x
They don't need live food ... I only used the convict eggs and fry to condition the pair I was trying to breed. Normally I gave them frozen food ... bloodworms, daphnia, glassworms and mysis shrimp.
If you want something that'll hunt fish, you'll want a bigger pike. Most of the dwarves are specialized feeders on dwarf cichlid fry only, won't even go after apisto adults (as food at least).