What are your ground temperatures and what is the proposed fish?
See earth contact and geothermal are great if the temperature you are going for is matched with your ground temperatures. But if you are hoping for the ground contact to help while raising tilapia but your average ground temp is like 58 F, well then it won't be so much help because you will still need additional heat or to use heat pumps to elevate the temperature since tilapia won't thrive till the water temp is above 70. (Tilapia survive between 55-70 F but they are not eating or growing much) So choose a fish that will still be eating at your ground temperature and you will likely be much better off.
The ground is a huge thermal mass, not an insulator. If you are trying to maintain a temperature above the ground temperature and you have a lot of ground contact, that huge thermal mass will be wicking the heat away to warm itself and since the ground is huge you might not want to pay that much in heating to bring it up to your desired temperature so it would be better if your desired temperature was in line with what the earth in your location has to offer.
But recall what I said about the ground being a huge thermal mass, are you really going to heat up the earth to keep a couple tanks of fish warm enough?
Research the ground temperatures and your proposed fish before you ground couple. If your desired temperatures are warmer than the average ground temperature at your location, then you would be better off insulating and using water tanks or other thermal mass inside the insulated envelope.