Might I suggest a toby or sharpnose pufferfish. They would be able to live in there for the rest of there existance, but it would be a good idea that you upgrade to a 40-55 gallon within 2-3 years for a sharpnose pufferfish. Someotherfish I would suggest are grammas, gobies, and clownfish. Only 2 other fish I would recommend.