yes you can...............however you would be required to change 75% of the water weekly. Ok, i have too add this little note here, I raise Goldfish and Betta's. Goldfish, as small as 1 to 2 inches will only grow 1/2 inch every 6 months so you'd have lots of time before being required to buy a larger tank, we have allot of kids here and kids are not Pro's. They assume "A Lot". Exaggerate allot. In reality now, its nice if we can all afford a 55 gallon, however most people want companionship, not the largest tank someone else can afford, everyone is not made of money and we all know it, however kids think everyone is "rich". That is why alot of parents have troubles with their children.
Professionally speaking.