It is hard to say how long it would be fine, maybe a year ,maybe two or three maybe longer will be fine ,it will depend on how much food you give it and the water conditions you have it in. I would say about three to four years and if it was at all possible I would try to get it into a bigger tank as soon as possible. But thats just me. Goodluck and I am glad you are thinking of your fish's well being. :clap: