i might also go a salt tank with a single panther grouper. i had my panthers in a 55, but they werent that big. but to keep one for life in a 125 would be awesome
One fish or one kind of fish? If one fish, I would say a glass banger like a jag, red devil, flowerhorn...something along those lines. If one kind of fish I would go with a colony of fronts or RBP's.