Pelodiscus sinensis. Put yours apart, they are higly agressive from the begining, and the bigger one will soon start bulying the other. More then one just in a place like a pond. You will need to a place for them to get out of the water. The diet is mainly carnivorus with some ad of herbivorus stuff like pleco pellets. It is very important to avoid feeders or any complete fish by that matter, they will eat themselfes to death very easily. Turtle, koi and chiclid pellets, alongside earthworms, slugs, snails, insects and the ocasional lean meat and fish fillet in small chunks will do as diet.