Obviously it is the scent that makes these foods so appealing to felines, perhaps triggering some instinctive craving, not unlike a human's craving for greasy, baked goods. However, it could just as well be a learned taste preference. Also, the stereotype teaches people that cats like fish, who then feed their cats fish, and the cats in turn prove their care giver right by developing a taste for it. That cats don't only eat what is good for them, but also posses the ability to learn taste preferences is indisputable. Every day in households all over the world the true carnivore cat behaves very much like an omnivore, stealing muffins and bread, or indulges in fruit and vegetables, often even ingesting things outright harmful like chocolate or tomatoes.
Care givers have to accept that no favour is done for the cat by feeding fish as a main staple.
Fish, no matter if whole, dressed, raw, cooked, or canned will cause nutritional deficiency of some kind, which in turn will eventually lead to serious disease. If fish is to be included in the meal plan of the domestic cat, one may only do so sparingly as treats, or to entice a sick cat to eat. Other than that, the story of fish and cats shall remain a fairytale.