Also keep in mind that once you put it into your tank you are obligated, IMO, to keep it or destroy it should you not be able to keep it.
Once you put it in your tank, especially with fish and rock from other areas of the world, it is exposed to diseases and parasites not native to your area. Releasing it introduces these back into the wild, not to mention it takes a fish that is used to getting food without having to search for it.
Research the fish, know what it is before ever putting it in a tank. Could be something you DO NOT want.