Salmon, Trout, and Whitefish Family

Chapter I -10

Salmon, Trout, and Whitefish Family 


The Salmonidae family which includes the trout, char, whitefish, grayling, and salmon deserves a chapter of its own. Often the simpler name salmonid is used. As a group, these fishes are probably more important to more Alaskans and over a longer period of time than any other group of fish. They are also the most studied and best understood group of fishes in Alaska. 

Salmonids are native to northerly latitudes of Europe, Asia, and North America. In addition, of course, they have been widely introduced in many cold-water locations worldwide. Many salmonids are anadromous and all spawn in freshwater. Some, especially salmon, are extremely important in commercial, sport, and subsistence fisheries. Others, such as Arctic grayling, are more important in sport fisheries. Most are important culturally.  

The salmonid family includes three subfamilies with a total of about 70 species. The subfamily Coregoninae includes the whitefish and ciscoes; the subfamily Salmoninae includes the salmon, trout, and char; and the subfamily Thymallinae, the grayling. In Alaska, we have 8 species of whitefishes and ciscoes and 13 species of salmon, trout, and char, including the introduced brook trout and Atlantic salmon, and a single species of grayling. 

All salmonids have an adipose fin, a small, fleshy fin that has no rays. The adipose fin is located between the dorsal fin and the tail, or caudal fin. The function of this fin is not known, but there is some evidence that it may have something to do with swimming hydrodynamics. Some other fishes, such as smelt and catfish, also have adipose fins. Early in my career, I suggested that the adipose fin was there so we could cut it off as a way to mark or identify certain fish. Salmonids also have a small, pointed structure called an axillary process at the base of each pelvic fin. The function of the axillary process is also unknown but it may serve to streamline the fish. All salmonids have a swim bladder connected to the esophagus by a tube. This condition is called physostomous. All have cycloid scales and soft rays in their fins. 

Salmonids thrive only in clean, well-oxygenated water. Almost all spend at least part of their life cycle in moving waters. All are predatory or adventitious feeders, but their individual diets depend on the species, size, age, and availability of food that may range from zooplankton to other fish. 

Whitefish and ciscoes, as a group, are found in Alaska in all rivers north of the Alaska Range and the Copper, Susitna, and Alsek Rivers to the south.  

The grayling subfamily contains only one genus with one species in Alaska. They are not anadromous. The Arctic grayling found in Alaska is also found in northern latitudes across North America and Asia.  

The salmon, trout, and char subfamily is a somewhat more diverse group of at least 30 species in 7 genera including the taimen, sometimes called hucho, found mainly in Russia. The largest recorded taimen, reportedly caught in the Kotuy River in Russia, was 83 inches long and weighed 231 pounds. In more recent times, however, reports of fish heavier than 100 pounds and more than 5 feet long are rare. 

Here is a question. How many species of salmon swim in waters of the Pacific Ocean? Be forewarned, this is a trick question. Do you have a number? The correct answer is 8.  

One is the introduced Atlantic salmon. There are seven species of Pacific salmon. Two species are found only in the western North Pacific in Asian and Russian waters. These are the masu salmon and the amago salmon. These species are closely related to each other and some scientists consider them a single species. The five species of Pacific salmon found in North America include: pink salmon or humpy, chum salmon or dog, sockeye salmon or red, Chinook salmon or king, and coho salmon or silver. The name Chinook is a proper name and is capitalized because it is taken from the name of a tribe of Natives from western Washington State. Actually, some scientists argue that the rainbow trout or steelhead is also a salmon because the life cycle of the species is very similar to that of the fish we call salmon. There is also genetic evidence to support this idea. 

The masu salmon has both anadromous and nonanadromous lifestyles. The anadromous form is found in Far East areas on both east and west coasts of Japan and parts of Korea and Russia. The nonanadromous form is found in all of Japan except for the most southern parts. Masu salmon return in spring and summer but hold in rivers before moving to headwaters before spawning in August and September. Most spend one or 2 years of rearing in freshwater and between 0 or 3 years in the ocean as they mature. Most are about 18 to 25 inches in length and weigh about 5 pounds. Masu salmon are called “sakuramasu” in Japan, which means “cherry trout” because adults begin to return at the time of cherry tree blossoms from March to May. Details of masu salmon life history may be variable across their range. In many populations the females migrate to sea before returning to spawn but most males remain in freshwater and mature there, awaiting the return of the females. 

Most amago salmon are nonanadromous but some are anadromous. Most of those that do migrate to sea remain in bays and inlets and few migrate to the open ocean. Of these, most spend only about 6 months in the ocean. Amago salmon are found only in a small part of southern Japan, mainly on the island of Honshu. Although the return migration is in May, spawning is in the fall. Juveniles spend 1 or 2 years of rearing and less than 1 year in the ocean, if at all. Adults are about 5 to 7 inches long. 

In Alaska, there are 3 genera in the Salmoninae subfamily: Oncorhynchus includes the salmon and trout; Salvelinus, the char; and Salar, the Atlantic salmon. There is a total of 13 species, including 2 introduced species, the brook trout and Atlantic salmon. Most members in this widely distributed subgroup have a great variability in coloration, life history, and ability to adapt to local conditions and habitats.  

I have a little story I call “Redds for Pinks.” All fish in the Salmoninae subfamily except lake trout bury their eggs in nests called redds. I was out beside a stream one day when is spotted a small group of energetic pink salmon that were intently focused on a small area of the stream bottom and I was able to observe their spawning activity. The female was digging a redd and the males were chasing each other in a bit of a frenzy. I didn’t have time to watch the whole show, but you may have seen this activity too and maybe you have heard this story before, too. Trout and salmon spawn in riffle areas of streams. They dig a redd in the gravel to deposit their eggs. That sounds easy enough but do you know how they actually do that? 

First, it is the female who does most of the hard work, the heavy lifting. The males mostly just chase each other about and maneuver so they can be in the right spot when the female is ready to spawn. Actually, one male is trying to establish dominance and defend the space against the other males. And, the female doesn’t really dig a redd, either. All she does is turn her side against the stream bottom and rapidly flex her body and tail to create a hydraulic suction that lifts sand, silt, and small gravel particles up into temporary suspension so the fast-moving stream water can take over and push the fine particles downstream. You can feel how this works if you lower the flat palm of your hand to the bottom of a stream or a sink full of water and quickly raise it. You can feel the rush of the water from the suction that will lift loose particles into suspension. The downstroke probably moves some fines, too. Eventually, the fine particles have been removed and a pit is exposed. The female probes the pit with her anal fin to test the depth of the pit. When it is ready, she releases a cluster of eggs while the dominant male adds sperm. The other guys try to rush in, too. 

The bottom of the pit itself has little water movement and the eggs settle quietly in a hovering cloud of sperm or milt. The female moves forward and resumes her digging action. Clean gravel from this digging covers the first egg pocket and creates a new pit where another cluster of eggs is released and fertilized. The pattern is repeated until a number of egg pockets become surrounded by a mound of clean gravel and a pit remains at the upstream edge. It may take a day or more before all of this is completed. 

The hydraulics of this is fascinating to me. Simple suction is all that the fish needs to excavate the redd. Water velocity blows away the fine materials. Dead water in the bottom of the pit retains the eggs and sperm until they are covered by more gravel. More digging upstream covers the fertilized eggs. When it is over, flowing water penetrates from the upstream edge through the now porous mound of clean gravel so it can carry oxygen to the eggs and remove metabolites. 

Note that when it is all over, the eggs have been spawned in several small clusters in separate pockets, which are physically isolated from each other. Not all of the eggs are “in one basket.” If, for example, part of the redd has poor circulation, physical damage, or if some eggs die, there is a good chance that the eggs from other pockets will survive. It is important to note that the eggs must remain buried and silt free to survive. Eggs that are not buried drift away and soon die. Few predators enter the redd to feed, but they take full advantage of the drifting eggs that would not have hatched anyway. 

We can expand this discussion by considering different species and different-sized spawners with different strength and excavation abilities. Larger fish can move larger-sized gravel, so they can spawn in areas of higher velocity and, usually deeper water. This gives their eggs a survival advantage, because these redds are less likely to be disrupted by other spawning fish. 

It was interesting to watch those pink salmon work on their redd. And I thought about how easy it is to simply say that trout and salmon spawn in redds which they dig in riffle areas. As usual, however, there is a lot more interesting story behind a simple observation.  

Let us assume that the trout and salmon life cycle begins with those fertilized eggs in a redd. What happens next? The embryo develops and before long, the eyeballs and a primitive spine become visible. Hatching occurs in about midwinter and the larva, called an alevin, wriggles out of the broken egg shell with a bright globule of oil in its egg sac. The alevin stays in the redd and, in fact, works deeper into the gravel. After the yolk has been absorbed, the diminutive fish works its way upward and emerges from the gravel as a free-swimming fry. During the fry and juvenile stage, most trout and salmon develop a series of vertical bars on their flanks. This life stage is called a parr and the vertical bars are parr marks. Parr marks usually disappear when the fish become adults. 

Among anadromous fishes, the parr grow until they become smolts, which is the life stage for migration to the ocean. Smolts lose their parr marks and become bright and silvery. Their physiology also changes as they transform from a freshwater organism to a saltwater organism. In the ocean, food is more abundant and they grow and mature until they return to freshwater to spawn. 

By the way, do you realize that salmon are strange fish? They are strange fish indeed compared to most other fishes. In Alaska, salmon are abundant and accepted as quite ordinary, but compared to other fishes, they are quite unusual. Do you know how weird and unusual salmon really are?  

To begin with, do you know that they are semelparous? Of course you do. Semelparous is a scientific term that means that the fish spawns only once, and then has a physiologically pre-programmed death. How weird is that? Most fish spawn a number of times before they die. The term for that is iteroparous. Salmon, in fact, are among the rarest of fish (less than 1% of more than 30,000 species) that are capable of spawning only once in their lives. Another fish that is also semelparous is the American eel, an East Coast fish. (Recall that salmon are anadromous but American eels are catadromous. Catadromous fish live in freshwater, where they grow and mature but migrate to the ocean, where they spawn and die.) 

What about spawning? Here, again, salmon are unusual. Although most fishes are broadcast spawners—meaning that they just release eggs and sperm and the fertilized eggs drift away—it is not uncommon for fish to provide some sort of nest or protection for the eggs. Salmon are unusual, however, because the female salmon is the primary caregiver, the male usually provides care for the young of most other species. Few other species provide as much protection as salmon. Salmon certainly can excavate a lot of gravel when they make a redd where the eggs are buried. Also, the alevins that hatch from those eggs are bigger than the hatchlings of almost any other fish aside from sharks.  

Hmm . . . think about this. This means that salmon are among the rarest of organisms that are born as orphans and die without offspring. It also means that every salmon we catch before it spawns is a virgin. Doesn’t this break a cardinal rule of fisheries management: to allow individuals to spawn, even if only once, before they are harvested?  

And what about those eggs? Most fish lay eggs but most fish produce a large number of small eggs. By comparison, salmon produce a relatively small number of very large eggs. What other fish, for example, can you name that has eggs large enough to put on a hook? 

Some populations of salmon make truly heroic migrations. Some Yukon River Chinook and chum salmon spawn in Canada, 2,000 miles upstream from the mouth. Some of these fish migrate 2,000 miles out to sea and some migrate around the North Pacific Ocean every year for 3 or 4 years, and each year in the ocean, a rotation may involve a thousand or more miles. Few other fish make such extensive migrations in their lifetimes.  

Where do we find salmonids? In cold waters. Small numbers of species of fish require cold water compared to the numbers of fish species that inhabit warmer-water habitats. 

Salmon grow fast, but do not live long. Most species of fish live to an older age than salmon. 

What happens during spawning? Salmon spawn in the fall or late summer whereas most freshwater fishes spawn in the spring. Many species become more colorful and some develop changes in body shape during spawning activities, but salmon take this to the extreme. Sockeye salmon, for example, stand out with some of the most dramatic and intense color changes. They transform from bright and shiny to gaudy red and green. Sockeye and pink salmon change in shape from an oval cross-section to laterally compressed. In some populations the change is truly impressive. And that kype. That fancy curved jaw of mature male salmon. And those teeth. No other fish has a kype and few, if any, grow fangs like salmon. Interestingly, semelparous species undergo more dramatic change in color and shape as they approach spawning compared to their closely related iteroparous relatives, such as rainbow trout-steelhead. 

Actually, there is more to color changes than that. Salmon, especially coho and Chinook salmon, undergo another dramatic color change in their lives. Juvenile coho and Chinook salmon, called parr, are multicolored with spots and vertical bars, called parr marks, so they are camouflaged for life in freshwater streams. When they become smolts, they develop the silvery color of adults and migrate to salt water.  

So there you have it. Salmon. Spawn and die. No living parents. Die with no offspring. Big eggs and big fry. Migrate thousands of miles. Live fast. Change color. Change color again. Love that cold water. Grow a kype and fangs to look pretty and prepare for combat.

Don’t you agree? If salmon are not weird fish, they really are pretty strange fish compared to most other fish species. 

References: Groot and Margolis, eds., 1991; Mecklenburg et al., 2002; Morrow, 1980; Quinn, 2005.