Problems arise in cooked fish such as salmon and tuna when it's improperly prepared. That grey-oily tuna meat is the blood line. It should have been removed before the tuna was cooked. The same is true of the flesh under the dorsal fin and along the belly. That is where the nasty flavors come from. The flavor of fish fat is about the same as cod liver oil. Prepared properly, both salmon and tuna are excellent fish. Yes, they do have a pronounced flavor, just as beef has its own flavor. But it's not that fishy flavor that is much like the smell of a fish shop. As for swordfish and brook trout, they taste very similar to me. Brook trout that's been brought to life in hatcheries is very mild in flavor. I prefer wild trout, with that beautiful light orange flesh. But that's my choice.
Not everyone is going to like strong flavored fish, or even medium strong flavored fish. My eldest daughter doesn't like cooked salmon or trout, but loves swordfish. I'm not crazy about some of the extremely mild fish. To me they are boring and tasteless.
I think it has something to do with the sensitivity of our taste buds as well. As a kid, I hated rye bread with caraway seeds, and horseradish. As I grew older, as with everyone, my tastebuds lost some of their sensitivity. One day, I found that I loved rye bread with caraway seeds, and horseradish. The flavors of the ingredients hadn't changed. But my sensitivity to them did. Salt became less salty. Horseradish had less bite. Unfortunately, though I still love them, blueberries don't taste as amazing as they did when I was a kid. It's simply the nature of things.
My point is, you may not like the flavor of a kind of fish today. But in another ten years, it may taste wonderful to you. And a tip for the op. Your partner may not like the flavor of some kinds of fish. But that doesn't mean that if you do like them, you can't have them. Try making the fish in foil packets, with a bit of butter, some sliced potatoes and carrots. Both of you will have what you want, individualized to your taste preferences. She doesn't even have to have fish in her foil pouch. She can have chicken, or beef, or whatever. you will both enjoy a good meal together, and that's what eating together is all about, enjoying it together.
Seeeeeeya; Goodweed of the North