As long as you eat fish with more selenium than mercury, essential selenoenzymes are never inhibited to a meaningful degree. Vast majority of fish have more selenium than mercury. Exceptions are pilot whale, shark, tilefish, king mackerel and swordfish.
Are You Worried About Mercury in Fish? This Graphic Can Help
Done this since I was My maternal grandpa's dad was a fisherman and he raised his family on the river. My grandpa owned his own fish market and taught us all how to catch and skin a catfish. They are always better fresh.