I reccommend keeping Americam bullfrogs in outdoor ponds if you have the space. Be sure to surround the pond with walls at that are at least as tall as the length of your frog. I reccommend covering your frog enclosure with sturdy screening because it's easy to underestimate their jumping capabilities. I keep my frog, which is almost 4 inches, in a kiddie pool 4 ft in diameter and about a foot tall. I cover the pool with screening and secure it with 8 sturdy clips. A rule of thumb is to provide a foot per inch. So, your 2.5 inch frog can be kept in a 20 gallon long aquarium. Of course, I reccommend that you use the biggest cage available.