When most people think about Japanese food, they think of sushi. Contrary to popular belief, Japanese people do not eat sushi very often but that's not to say that they eat don't fish. The most popular way to eat fish in Japan is by grilling it with either a little bit of salt or soy sauce.
If there's one word to describe Japanese cuisine, it's "simplicity". There's no heavy sauces or tons of spices in Japanese cooking. They just add a little bit of salt here and there to accentuate the natural flavors of the ingredients. It might seem bland, but sometimes simple is best. Salmon, snapper, mackerel, and fresh water fish are usually cooked by grilling.
Another way to eat fish is by marinating it in a sweet soy sauce based marinade and then broiling it. Yellowtail is the popular fish which gets cooked this way.
You can even cook fish by steaming it. Usually a whole fish is steamed with some root vegetables (lotus root) or rice and flavored with salt or soy marinade. Again, simple preparation.
You can even fry fish and serve it with a dash of salt and lemon. Small light fish such as smelt and blowfish are perfect for frying.
And last but not least, you have your sushi and sashimi. Always delicious!