What are more accurate dimensions of the tank? Is it 2 foot by 2 foot by what? It's best to not only know the size of the tank, but the amount of gallons it will hold. Traditionally, it's best to have 1 gallon of water per 1 inch of fish. And, the fish should be measured by the maximum length of the fish when it will be full grown. All fish start out small and then mature...you want to know the mature length of the fish. Additionally, you have to take into consideration your filter system, heater, compatibility and mating habits of your selection. Plus, certain tanks are just better for certain fish (i.e. some fish like longer tanks to openly swim, some like deep tanks to dive, some need rounded tanks because they can hurt themselves with rectangular corners.)
And finally, a tank is like a neighborhood. Certain fish like swimming high, low and in the middle of the tank, or live in rock caves, and will claim their territory. Some fish are bullies and others peaceful. You also want fish that eat the same type of food and not each other. You will not only want a fish that pleases you but fish to do some of the cleaning duty as well.