OK. That is the question. And from the Big Site of Amazing Facts, we find this information.
What Is the Difference Between Trout and Salmon, How Are They Related, and How Do You Tell Them Apart?
Trout and Salmon are so closely related that some fishermen and scientists have trouble classifying the individual species. Technically, Trout is a species of freshwater and saltwater fish. Salmon belong to some of the same family as trout but, unlike most trout, most salmon species spend almost all their lives in salt water. Both Trout and Salmon are classified as an oily fish.
The steelhead and rainbow “trout” are actually the same fish. The name steelhead is used if the fish is able to make it to the ocean, and rainbow refers to those that are landlocked away from saltwater.
In 1989, when DNA tests showed that the rainbow or steelhead isn’t really a trout after all, the fish was reclassified as a salmon. Likewise, the Atlantic salmon was determined not to be a salmon after all, but a trout.
As another example, the sockeye salmon is called the kokanee or silver trout when it resides in fresh waterways.
And then from Trout Fishing Help we find,
Most people know that trout and salmon are the same family (salmonid). Char, grayling and whitefish also belong to the salmonid family. One of the things that distinguishes fish in the salmonid family from other fish is that salmonids (trout, salmon, char, grayling and whitefish) need clean, cool water and a healthy habitat to live in. This why invasive species and plants are such a big deal when found in these environments – they threaten the population of salmonids.
Of the salmonids, trout and salmon are very closely related and most trout anglers enjoy catching salmon and vice versa. Just as there are many different species of trout (rainbow, brown, brook, lake, apache, gila, steelhead, etc.), there are different species of salmon (coho, chinook, Atlantic, sockeye, and chum). And to the untrained eye, it can sometimes be difficult identifying your catch (especially since these fish have a lot of similar characteristics).
The easiest way to to tell the difference between salmon and trout (when in doubt) is to count the number of rays on the anal fin. All trout have 12 or less rays in this fin, whereas salmon have 13 or more rays. This rule is an interesting bit of trivia, it can be useful in helping you identify the difference between trout and salmon.
So there you have some information. So what brought this up? This morning we had trout for breakfast – at least that is the way it was presented. It was pink. So I just had to ask the question. Robin said, “Google it.” I did and you have just read the results. Cheers!