I just said the same thing on The Puffer Forum, but you should be cautious as the fahaka may get injured by the spines of the Ctenopoma if it attacks them
I'm not too concerned with the spikes. Unless he was able to swallow the Ctenopoma whole, I don't believe they can really do any damage. I've fed him large crayfish that were able to get their claws on him and not do any damage.
If I notice the Ctenopoma is showing signs of stress I'll remove him though. They are doing great so far