I know a guy that lives near me with a huge outdoor pond. The groundwater around our area has saltwater intrusion, so his artisian well brings up brackish/saltwater up from the ground into his pond which is about 200 ft by 50 ft. He keeps native fish that come from the brackish waters around here. He has tarpon, snook, cobia, tripletail, jacks, snappers, stingrays, red drums, and black drums in it. He feeds them scraps of yellowfin tuna he gets from the charters he runs.