Wow, that seems odd. How big is your eel? Have you actually seen him take down the fish? Are you sure he's taking them and they aren't just dying and being cleaned up before you see it? From what I understand, snowflake eels aren't much for hunting and catching fish. They have flat molars for crushing shells of shrimp, crabs and such. If he is guilty, your only alternative may be to trade him in for another. Or maybe do a species only tank.