I was just taking my training for my new job, and our aquatics expert assured me that yes, it's bad to keep goldfish in a bowl. The amount of oxygenated water in a bowl is supposedly not enough to keep a gold fish healthy, and if you have more than one in a bowl it can prohibit their growth.
When I was a kid, I had two goldfish sharing the same bowl (and it wasn't the largest bowl, either). We didn't have a filter or an oxygen pump, either. They seemed to grow up fine until they hit what, back then, to Young Me, was "fully grown". After a while we decided to set them loose in a public pond, and my aquatics expert assured me that was all-around better.
PLEASE, PLEASE, PLEASE, do not release any pet into the wilds. Living here in Florida, unfortunately people will do that. Until the cold winters a few years ago it was kind of cool to see the wild parakeets. The BOA constrictors reeking havoc in the Everglades is not all that great. Releasing a pet that is not native is a cruel thing that you can do to the wildlife and their enviroment