um, maybe a small group of exodons? they are like mini piranha. go to youtube and look up exodon feeding. they are also called buck tooth tetra i to believe. they are not always easy to find tho. the small tanks really limit your options because many fish sold in everyday fish stores will outgrow those tanks within 6 to 8 months if cared for properly. if you dream of larger tanks you could get a baby cichlid of your choice like a jack dempsey or something of the sort and use your smaller tank as a grow out and save money for a larger tank from craigslist or something. i just got a really nice tank for 75 bucks. its a 55 gallon breeder. 36 inches long 18 inches from front to back and 20 inches tall. 1/2 inch thick glass.