The Complicated Tale of Salmon and Trout

a graphic of 10 illustrated fish
Here is a selection of salmon from around the world. Salmon change color and shape during mating season. These are male salmon as they appear during mating season. (Smithsonian Institution)

Salmons are special fishes. Generally, fishes either live in freshwater or the ocean, but salmons often live some part of their lives in both. They are anadromous fishes, meaning they spend part of their life living in freshwater streams and part of their life in the salty ocean. There are many species of salmons that live around the world, and surprisingly many of the fishes known as “salmon” are not each other’s closest relatives. The family Salmonidae includes the salmon, trout, char, freshwater whitefish, taimen, lenok, and grayling. However, when talking about salmon, the discussion is generally referring to two different groups—fishes in the Oncorhynchus genus and Salmo genus. Salmons in the Pacific, including the Chinook, chum, and sockeye, are members of the genus Oncorhynchus, and are closely related to trouts, like the rainbow trout, in the same genus. The Atlantic salmon is a member of a completely different genus, Salmo, and is likewise related to trouts in the same genus, like the brown trout that’s native to Europe. Both groups contain fishes with the common name “salmon” and the common name “trout.” 

Often, recreational fishermen will distinguish salmon from trout by where the fish live. “Salmon” split their lives between rivers and the ocean, while “trout” spend their entire lives in freshwater. But this designation is very simplified and falls apart when considering that some species do both. The rainbow trout has populations that spend their entire lives in freshwater, and populations that spend part of their lives at sea. These ocean-dwelling rainbow trout are also known as steelhead trout. The cutthroat trout and cherry salmon similarly have riverine and oceanic populations.

Regardless of whether they are ocean-dwelling or not, a salmon’s life often begins and ends in freshwater. When the larvae, known as fry, hatch from their eggs, they are often far upstream in inland tributaries, and depending upon the species, then make their way to the ocean. In the ocean, the fish grow quickly—sometimes doubling their size in a single summer. After one to five years, the mature fish return to the rivers where they were born. This annual migration is called a salmon run. During this time the mature salmon transform into the beautiful pink and red colors for which they are known. In some species, the males and females will change both in color and shape, with the males often presenting much more dramatic colors and hooked upper jaws. Each species has its preferred spawning environment, often dictated by the size of the river, speed of the water flow, and the size of the gravel in the riverbed. Once the final destination is reached, females create a depression in the gravel where they lay their eggs. Then the males disperse their sperm around the egg and the female covers the fertilized eggs with pebbles. Parents will guard the nest for either a couple of days or weeks depending upon the species.  Once their parental duties are complete, many salmons will die.  

Below, several salmon species are listed and discussed in greater detail, including the steelhead trout. 

(Oncorhynchus tshawytscha)
The king of salmon, the Chinook, are the largest of them. On rare occasions they can even reach 100 pounds, though most large Chinook are closer to 50 pounds. Many Chinook travel hundreds of miles to get to their spawning grounds, a distance that requires months to arrive at their destination. Chinook have two annual salmon runs, one in the winter and one in the summer. Those with a greater distance to travel begin in late spring and summer and reach the spawning area at the same time as those that run in the winter that are closer to shore. Large in size, they are the least abundant of the Pacific salmons.

Black Sea
(Salmo labrax)
The Black Sea salmon lives in the rivers, lakes, and northern region of the Black and Azov Seas in Eastern Europe. Some populations are anadromous, meaning they migrate from the salty Black Sea to rivers, while others remain in the rivers and lakes in the surrounding area. It is particularly abundant in the Lim, Kuban, Don, Dniester, and Dnieper Rivers, and Lake Plav in Montenegro. In recent years, the sea-going population has been in decline, potentially due to the construction of dams. The Black Sea salmon is sometimes identified as a brown trout (Salmo trutta), and there is an ongoing debate among scientists as to whether the two are separate species or one.

(Oncorhynchus kisutch)
Coho salmon are masters at living in small, shallow tributaries. For this reason, they are often found in coastal brooks and streams, even near neighborhoods and cities. They often use rainstorms to their advantage, waiting for the rise in water level before attempting to swim upstream. Most are also homebodies and stay within a hundred miles from the mouth of the rivers where they spawn. Coho are prized catches for anglers, as they are one of the least abundant Pacific salmons. 

(Oncorhynchus keta)
Chum salmon are also known as dog salmon, likely due to the set of distinct canine teeth that protrude from their mouth during spawning. Males have a very distinct red and black stripe pattern on their sides during spawning season. Chum and Coho often spawn in the same rivers and can generate hybrid offspring, often though the larger chum stay in deeper sections of the river, closer to the ocean. 

(Salmo ciscaucasicus)
True to its name, the Caspian salmon lives in the Caspian Sea. These salmon prefer cool clear water with fast currents and gravel bottom, and many breed in the Terek and Kura Rivers. Like the Black Sea salmon, populations are in decline following the construction of several dams.  The dams cut off the fishes’ historical spawning migration routes, and those that attempted the route were fished out by locals taking advantage of the massive aggregations of salmon by the dams. 

(Oncorhynchus gorbuscha)
Pink salmon are the smallest of the Pacific salmons and are easy to distinguish from other salmon species by the characteristic hump on the males’ backs during spawning season. It is for this reason that they are nicknamed “humpies” or the "humpback salmon.” Though small, they are also abundant. Pink salmon prefer large rivers close to the ocean and the newly hatched fry quickly make their way to the ocean estuaries. Sometimes adults will even spawn in brackish estuaries, never traveling up a stream. Their fry are different than most species of salmon, as they lack spots.

(Oncorhynchus nerka)
Sockeye salmon are a prized catch for fishers due to their especially flavorful meat, which is a product of their rich plankton diet. Unlike other Pacific salmons, sockeye salmon fry live the first year of their life in a lake. They also have some of the largest salmon runs during spawning season. The sockeye salmon run can bring over a million individuals together, an impressive congregation of leaping fish that draws tourists to the Adams River in Canada every year. Bristol Bay in Alaska is home to the largest Sockeye salmon fishery in the world. 

(Oncorhynchus masou)
The cherry salmon, or yamame, lives in the Western Pacific, along the shores and in the rivers of Japan. Some spend part of their life in the ocean, however, like the steelhead, certain populations of this species only live in freshwater streams. They are named for the cherry blossoms that are in full bloom during the annual spring run. In recent years scientists have debated if the amago salmon is the same species as the yamame or not, with a distinction between the two is the presence of red spots in the amago. 

(Oncorhynchus mykiss)
The steelhead trout is the name given to rainbow trout that migrate to the sea. While they physically appear to look like all other rainbow trout, steelhead are anadromous, meaning they spend part of their life in rivers and part of their life in the ocean, just like salmon. Unlike most salmon, Steelhead do not die after spawning and can breed several years in a row, though it is rare to see a four-year spawner. Like Chinook, steelhead have two different spawning seasons, a winter run and a summer run. Steelhead trout are sometimes sold under the name Steelhead salmon since they have the same pink flesh as all other salmon. 

(Salmo salar)
There is only one species of salmon that lives in the Atlantic Ocean and so it is appropriately named the Atlantic salmon. This salmon travels up rivers in the northern parts of North American and in Europe. Unlike its Pacific cousins, Atlantic salmon can spawn year after year, returning to the ocean in between spawning seasons. North American populations were hit hard by habitat loss and overfishing following European settlement in the 1600s and 1700s, with forest clearcutting, beaver trapping, and dam building being main drivers of population decline. Due to population concerns, there is no commercial Atlantic salmon fishery in the United States, though most farmed salmon were originally bred from Atlantic salmon.

June 2022
Tags: Salmon