Some very popular fish have the potential to grow to more then a foot. Rarely do I see fish this size in the aquarium. With the exception of eels. This fish include angels, triggers and groupers.
You may not see many Triggers get over a foot in the home aquarium, though Queen Triggers do get very large, but Angels, Tangs, Groupers and Snapper routinely get over 1 foot, some even up to 2 feet.
Reason being most people have tanks under 120 gallons and want coral to grow . Having a 12" fish is not a priorty .
I have a few tanks , besides my reef , my lion fish tank has 2 volitan lion fish at just about 13". Also I have fresh water stingrays that are well over that.
I'll have to get a better picture later, this is from a few months ago. This thing is starting to turn into a menace, he just bit through the HOB filter intake tube and ate the airstone I had in the corner of the tank