+1. An interesting anecdote to go along with this, at the National Aquarium, our main exhibit on the first floor is Black Tip reef. The exhibit is a huge artificial coral reef with a large open space in the center. Most of the animals (the tangs, triggers, rays, sharks and Calypso, our turtle) spend their time out in the middle of the exhibit or in the sunken underwater viewing area. There are a few clownfish, however, that hang out in one spot, and only one spot. Here's a rough picture of the layout:
The large red circle is where most of the animals can be found. The tiny, tiny red circle in the top right hand corner is where these few clownfish can always be found. To be honest, I'm surprised they don't starve. All the food is broadcast over the red circled area and where the sharks are in the picture above. No food is given to any animals on the periphery. Yet, they've survived for months in the exact same spot. I can always find them there, in the same exact artificial Acropora colony.
I don't mean to say the clownfish never move. They obviously have to go get food since they're not target fed. But your point is very accurate and germane to the conversation. These clownfish probably spend more than 99% of their time in an area smaller than that of a standard 10 gallon tank. I can't say whether they'd "rather" be in the ocean. I doubt clownfish are even self-aware, and such philosophical questions require self-awareness, and the knowledge that they are not, in fact, in the ocean. I can say the Black Tip Reef is over a quarter of a million gallons of seawater. It's probably as close as you're going to get to a real coral reef in captivity. Yet, these clownfish choose to live in a dark little corner of the exhibit by the escalators.
EDIT: that's not to say that any fish can be shoved in any space and survive. I'm merely echoing the statement that the natural behaviors of some fish occupy very, very small areas. Tangs are not one of these fish. Their natural behavior can have them travel dozens of miles a day.