Well, the thing is hungry...fish fit in mouth....fish will eat fish. Thats kinda their nature...
Its hard to find tankmates for lions but the rule of thumb is...buy sumthing that wont fit in its mouth. Do that and yer fine. Also, u gotta find fish taht wont hurt the lion either. Now, anglers are slow moving, easy to gulp down...damsels are natural food. I would go with tangs, wrasses, other lions, eels, some triggers, butterfly fish and angels. Anything else, it probably wont work out.
Also, anglers arent really a community tank species, they are more of a species only creature. Cuz they are kind of like lions as well: they eat wat fits in the mouth, or are eaten...except u seldom keep afish in the normal home aquairum that can chow down a lion. Anyway...hope that helped