Well I would just like to say that I think that bowls are cruel. Mostly because they slowly suffocate the fish, partly because it's not enough space or enough of an environment for them to thrive. The size of the tank is not important when deciding what fish can fit in it. It's the amount of surface area. The reason being that the top of the water is where the gas exchange occurs. Thus allowing the water to have the oxygen to support fish. A filter serves partly to help to get more oxygen into the water and partly to clean it.
If you want a fish but you don't have alot of space I would suggest looking at those mini tanks, they work pretty well if you don't fill them with fish. Pick up a book at the library or something and look at what it says, those books will help you alot with figuring out how to chose a tank and how to chose fish for it. I think that for the mini tanks the best fish are small ones like guppies or tetras. Guppies breed very fast so be aware of that, tetras however come in many shapes, sizes, and colors and don't breed particularly fast.
Also, for those of you that have tanks or are looking for some, DO NOT EVER change all the water that the fish is in at once. You will probably shock it to death. If you have to take the fish out, keep it in a clean container and fill the container with water from the tank, or at least a good amount of it. When cleaning the tank, don't empty it all at once. Empty half of it ideally, if you have to change all of it utilize plastic bags and there are chemicals you can add that will make the water more suitable for fish life.
I know a good amount about this, if you have other questions let me know. If I can't tell you I can look it up.
Plus, those books are very helpful and not expensive.