Thanks for the bug report. This isn't actually to do with fish directly, it is because this mod changes the character's icon to that of a fish. Presumably your conflicting mods are changing either the character icon or the fish icon, either of which could (depending on how it is done) break this one. My code (incorrectly) assumes certain things, that might not hold up under these circumstances.
I'm not sure how well this mod would go with Bob's Custom Classes and/or RPG Mechanics anyway to be honest. But I can have a look at releasing a fix today.