Keeping fish in a goldfish bowl is not a good way to help your finned friend live a long and healthy life. Even goldfish require some sort of filtration for the water. In a simple bowl, they will be swimming around in their own waste which will soon become toxic and cause them to be susceptible to any disease which will kill them well before their time.
Of course, if you really want to use a bowl, you could mimic the job of a filter by doing a partial water change every week. You will also need to keep the bottom very clean and, of course your goldfish will need a pretty big bowl to be his happiest ( I would say at least 10 gallons). Don’t overfeed the goldfish as this will cause his water to get toxic quicker.
But living in a bowl is boring (would you want to do it?) so why not get a nice tank with proper filtration and lighting and treat your goldfish to a real home. With proper care your goldfish can live quite a long time and you’ll be able to house several goldfish in a tank which will look a lot nicer than one lonely fish in a bowl.
The size of your tank depends on how many goldfish you want to have in your care. Each fish should have about 7 gallons of water, so if you want 5 goldfish a 35 gallon tank is recommended. The tank should have the proper lighting and a filter but take care that the filter does not create too much current if you are caring for the fancy goldfish with the long flowy tails (it will make it hard for them to swim!).
Another fish that is commonly kept in a bowl is the Betta or Siamese Fighting Fish which is a mystery to me since they thrive in water temperatures of around 75 degrees – a bit warmer than the normal unheated goldfish bowl can supply. One of the main reasons for this must be that these fish actually get their air from the surface of the water and don’t need any their water to be oxygenated by the action of a filter or air stone. Just like the goldfish, however the water in the bowl will become toxic to the Betta and eventually kill him.
So if you want to keep healthy happy fish and not have to run out to a pet store every week to replace your dead goldfish, get rid of the bowl and put them in a nice roomy tank of their own!