I've thought the same thing about my two fighting fish (Herb and Sushi - seperate bowls of course). And then one day Sushi's bowl accidentally broke while I was cleaning it. The only other bowl I had to put him in was a large gold fish bowl. So I set him in there thinking that he'll probably take advantage of the space and go crazy. But for weeks and months he just kept in a little space at the bottom of the bowl. No matter how much space you give them, I don't think they really care too much for a lot of long distance swimming.