While it is possible to carry and/or ship fish back to the USA, we generally do not recommend it. It can be costly and not worth the trouble.
To carry fish on the plane, it needs to be frozen, and you are not allowed to have it packaged with ice, dry ice, or any type of chemical refrigerant. I have seen people freeze it solid, wrap it in newspaper, and carry it in a cooler.
To ship it, it would likely cost you more than it would to purchase it back in the USA.