Are there any freshwater crabs or any other type of freshwater pets?

Search up some info on yellow belly sliders, red ear sliders, and box turtles. they all make very good pets. But, it depends on your tank size. If you have a 20 gallon long tank then id look into a box turtle. If you have anything bigger then that, then consider the other two types. All that you would need to get are a basking dock, a heat lamp, and a UVB lamp.