Yep that sounds like a likely mechanism of injury to me as well.... fahakas are not territorial, they are not like cichlids and will just bumble are the space they have as they please. I hate to say it but if he is chasing fish, I think he means to catch and eat them. My fahaka is more of a ambush hunter but occasionally I have seen her chase, hunt and murder a particular fish who she thinks has wronged her in some way. The caves will help but long term I would be careful... seeing a fahaka eat a live fish is not for the faint of heart lol