We have a fast food place called Long John Silver's for fish. Not the best. Their chicken may be better than the fish.
Archer Treacher's Fish and Chips is another chain, it is slowly coming back after closing most of its stores.
Other fast food chains usually have a fish sandwich and none of them are very good. Their ads sometimes make them look good but they do not taste good. Lots of bread and lots of tartar sauce, sometimes a slice of cheese, but the fish itself is usually not so good.
There are fish markets, some will cook the fish you buy, and some are specialty fast food fish and shrimp places. I do not stop at any of those.