Salmon and trout both belong to the same fish family, along with grayling and chars. As a result, preparation methods for cooking the fish are largely interchangeable. Given the popularity both salmon and trout, they are regularly used to stock lakes -- and you can find them in most parts of the world.
You can typically find both trout and salmon in several different forms at your local fishmonger or supermarket. Salmon steaks are one very popular cut, while trout are among the fish you're most likely to see available whole. Both types of fish are also usually available in fillets. If you buy a whole trout, advisable cooking techniques include poaching, grilling, baking or, in the case of small rainbow trout, even pan-frying. You can also prepare steaks in the same range of methods, while delicate fillets are usually best pan-fried or breaded and fried. Whatever the cut, you should gauge cooking time based on the thickest part of the fish, checking that the flesh is cooked completely there.
One way of categorizing fish and deciding on the best cooking method is to note its oil content. In this respect, salmon and trout are more alike than they are different, as both fairly oily types of fish. Other oily fish include mackerel, smelt, kipper, anchovies, fresh tuna, sardines and swordfish. When fish have fairly high oil content already, they do well with cooking methods that don't rely on additional oils or fats. For example, you can bake, steam, grill or pan-fry either salmon or trout to excellent effect. Frying in oil or fat is less appropriate.
While trout and salmon are closely related and typically interchangeable in recipes, they do have slightly different flavors. Compared with the mild taste of most trout, salmon has a bigger flavor, sometimes described as sweeter. The texture of salmon also inspires many devoted enthusiasts, as evident in its central role in Japanese cuisine and the connoisseur-crazed status of particular types of salmon such as sockeye or king.
If you're deliberating between salmon and trout, you might compromise and try salmon-trout, also known as steelhead trout. Another member of the salmonidae family, the steelhead is very similar to the salmon in appearance, with the same coloring and texture. Just like salmon, the steelhead migrates upriver for spawning, spending the rest of their lives in the ocean. Both fish eat lots of krill, which produces the characteristic color. Finally, both have similar tastes and are well-suited to the same cooking techniques, including baking, steaming, grilling or pan-frying.