I hesitated a long time over the sardines, too, for the very reasons I've always avoided fish.
Sardines, human food, are not the same poor quality as what is put into cat food. And they are rich in the omega oils cats need. I have never fed fishy cat foods to my cats, nor do I ever give them human tuna. But, I think an ounce of sardine (half ounce for SK), packed in water, no salt or spices added, once a week should be okay. And I pick the bones out.
It may be less than once a week. Maybe every other Sunday if it causes me too much worry. But I've got two who don't like the fish oil. I haven't tried the krill oil yet. Supposedly that is less fishy. If they like that I won't need to give them the sardines as often as once a week. I'll drop it to once a month maybe.