The following discussion of the color patterns
of chum salmon has been adapted from an article titled "Color Variations
in Spawning Pacific Salmon" (by Jim Ames and Steve Schroder), published
in Breakthrough Magazine in 1995. We wish to thank Larry Blomquist, publisher
and editor of Breakthrough Magazine, for allowing the use of this copyrighted
material on the WDFW web site.
chum salmon entering freshwater to spawn. As discussed in the text
below, the color patterns displayed by these fish are very dynamic,
being affected by behavior factors and natural aging processes.
One of the most overlooked
of the many fascinating life history attributes of Pacific salmon is the
use of varying color patterns throughout the lives of this group of fish.
Few people understand the amount of variation that exists in the color
patterns of salmon, particularly during spawning, and that these variations
reflect the physical condition, degree of maturation, stock or racial
origin, and the social positions of individual fish. For most people,
information about salmon color patterns usually comes from photographs
of dead fish, or exhausted live fish that have just been caught on hook
and line (like many of the photographs presented throughout the Chum Salmon
Web Page). Salmon in either of these conditions do not display the colors
of living fish happily occupied with the goals of feeding, growing, and
ultimately producing as many offspring as possible.
In this article,
we will primarily discuss the colors of spawning chum salmon and include
photographs showing various color patterns displayed by this species.
These salmon color observations are the result of several decades spent
studying and observing these fish in streams from Oregon to Alaska. Our
goal is to explain some of the things you should look for if you get an
opportunity to observe live spawning salmon.
The variety of colors displayed by fishes is unrivaled in the
animal kingdom. Not only do fish exhibit just about every conceivable
variation of color, stripes and spots, but they also have the ability
to change colors and patterns depending on their environments, individual
moods, or life history phases. The physical basis of fish color and
the mechanisms controlling color changes provide insight into why fish
look the way they do.
Fish color is determined by
chromatophores, specialized cells that are present in the skin of nearly
all fish species. Chromatophores are irregularly shaped cells that take
many forms but usually are roughly circular with multiple radiating branches.
There are two basic types of chromatophores; those that provide pigmented
color, and those responsible for metallic, iridescent colors. The pigmented
chromatophores include melanophores (black and brown), erythrophores (red)
and xanthophores (yellow).
These specialized cells absorb
light, specifically, the complement of the color being expressed by a
particular chromatophore. Color intensity is controlled within these cells
by concentrating or dispersing pigment granules. When pigments are concentrated,
the skin will be lighter and the chromatophore's color will be suppressed.
Conversely, dispersion of pigment granules within a chromatophore will
darken the skin and enhance color.
The metallic chromatophores
include leucophores (white) and iridophores (silvery), and they contain
organic crystals that reflect light to display various metallic or iridescent
colors. Fish and other vertebrates have not evolved pigments for colors
in the green-blue-violet spectral range. These colors are produced by
iridophores reflecting light of specific wave lengths, or by the combined
effects of iridophores overlaid with other chromatophores. Pigment chromatophores
of differing colors can also overlay each other, and some can carry more
than one pigment, processes which add greatly to the overall palette of
There are various ways fish
produce or change their color patterns. The most fundamental color schemes
are the genetically determined (morphological) colors and patterns that
are specific for each life history stage. Such colors can be thought of
as the generic patterns that occur throughout the range of the species.
These general color schemes do show some variations in individual fish,
particularly in patterns of spots, stripes and bars. The generic color
pattern of the spawning chum salmon (our focus species) is dominated by
irregular vertical bars along the sides that vary in color in a set pattern
from black just posterior of the opercle, to various shades of red or
maroon in the middle of the body, and again to black along the caudal
peduncle. Other notable colors include dark, often black ventral surface,
and black ventral and anal fins with snow white tips.
Other types of color patterns
can be controlled and changed by the fish itself; and are the primary
subject of this article. These physiological changes are a response to
a variety of environmental and behavioral factors, and are under both
neural and hormonal control. Neural, or nervous system, control of color
can involve all types of chromatophores except iridophores. Spawning salmon
display a range of neurally controlled colors that often reflect their
sex and social status. The most obvious example of neural control (or
lack of it) is the change in color that occurs when nervous system control
ends - when a fish dies. Pigmented colors often fade, but silvery or otherwise
metallic areas (iridophores) maintain their normal intensity. Hormonal
control of color can take a variety of forms, but usually acts primarily
on the melanophores and can cause either a lightening or darkening of
the skin. Adrenaline, in particular, is known to concentrate pigment,
resulting in lightening of melanophores, which causes a blanching of skin
Five species of salmon (genus Oncorhynchus) occur along the Pacific
coast of North America, and two other species are found only in Asian
waters. Of the North American species, the chinook (king) and coho (silver)
salmon are the best known because of their wide distribution and renowned
sporting qualities. The sockeye (red), pink (humpback) and chum (dog)
salmon have long been thought of as commercial species, but these fish
are increasingly valued by sport anglers. Each species of Pacific salmon
has unique color patterns that vary throughout their lives and are the
most vivid and colorful during the spawning period.
Prior to spawning, Pacific
salmon undergo a series of remarkable transformations. They physiologically
change from a marine organism to one that can live in freshwater, their
jaws become elongated, large teeth may erupt through the gums, the skin
and fins thicken and scales are partially resorbed. Accompanying these
morphological changes are often spectacular species-specific changes in
body coloration. Naturalists have frequently pondered why spawning salmon
develop such vivid color patterns and at various times have proposed that
they allow the fish to recognize members of their own species, aid in
camouflage, increase oxygen absorption through the skin, and serve as
important intraspecific signals in spawning communities.
Mature salmon are
particularly interesting because their general morphology can vary regionally
and their body colors are temporally dynamic. In this article six factors
are described that can influence the color patterns of individual spawning
fish. For living spawners in their natural habitat, the most important
factors are discussed in the Social and Sexual Differences section, which
covers the complex color patterns used by the salmon to communicate social
standing and to compete for mates.
The color variations discussed
here are general descriptions, and it should be noted that individual
fish can vary greatly from the normal species pattern because of factors
like genetic mutation, disease, injury, or hybridization with another
species. Also, with the degree of color variability expressed by Pacific
salmon, it would be expected that some populations could vary substantially
from the patterns described below.
As Pacific salmon return from the ocean (or large lake systems) in the
last year of their lives, they exhibit typical pelagic fish coloration:
dark blue or green backs with silvery sides and bellies. This counter-shading
pattern can make a fish nearly invisible in an open-water environment
as illumination from above lightens dorsal surfaces and shading darkens
ventral surfaces. The silvery sides and belly reflect the general water
or background color, resulting in near-perfect camouflage. At this stage
females and males are almost indistinguishable, and it takes experience
and a sharp eye to differentiate sexes.
bright chum salmon showing the counter-shading colors that provide
camouflage for the fish in the open-water ocean environment.
salmon showing progressive development of the bar pattern as the
fish mature. The first fish is ocean bright, displaying only the
slightest indications of bars. The second individual exhibits increased
definition of the bar pattern, and the third fish is beginning to
change color from the silver-blue ocean coloration to the basic
green/yellow spawner color. The last fish shows typical coloration
when entering freshwater, and the light color in the center of individual
scales shows that it has not yet reached full spawning colors.
|© 2000 Steve
dead male chum salmon that has completed its life cycle and displays
pronounced scale loss in the caudal peduncle area, probably caused
by the bites of competing males. All fins exhibit fraying, and the
lower jaw shows some skin loss that may also have been caused by
fighting behavior. The light colored patches on the body surface
are sites of secondary fungal infestation.
increases as th e maturation process proceeds and the fish approach and
enter their natal spawning grounds. The silvery ocean-type coloration
gradually changes to full spawning dress, with the males of some species
displaying more vivid colors than the females. Each salmon species has
a characteristic spawning coloration, making identification relatively
simple during this life stage. Sockeye, coho, and northern stocks of chinook
adopt various shades of red or maroon as their basic spawning colors.
Pink salmon and southern chinook stocks vary in coloration from light
to dark brown. The chum is unique in color, with a greenish ground color
overlaid with patterns of black and maroon.
As mentioned earlier, marked changes in body form also take place as salmon
mature. Males develop characteristic hooked snouts and large spawning
teeth, and the body becomes laterally compressed. In a few species, males
may also develop pronounced humps. An often overlooked feature is that
the adipose fins of mature male salmon are substantially larger than their
female counterparts. Female body form does not change as markedly as the
male; the skin thickens to a lesser degree, jaws elongate slightly, teeth
become somewhat more prominent and developing ovaries fill out the abdominal
area. All of these changes are controlled by hormones and occur throughout
the range of each species.
Once sexual maturation
has occurred, Pacific salmon rapidly age, with death the ultimate result.
Males engage in ritualized battles and simple aggression to gain access
to potential mates, and females use their caudal fins to prepare two to
seven nests which they guard until death. These behaviors cause physical
changes in their color patterns. Because of their repeated fighting activities,
the skin adjacent to the dorsal fin and caudal peduncle of males is often
abraded and turns a light tan or white. The caudal fin and peduncle of
females not only becomes abraded but skin, muscle tissue and fin rays
are eroded. In general, the vivid color patterns on both sexes become
occluded because of injuries and fungal infestations as the fish approach
death. The duration of the spawning process is variable, but all five
of the Pacific salmon species die within several weeks of the initiation
2. Latitudinal Differences
Within a salmon species, spawning colors are usually brighter and more
vivid the farther north the spawning distribution occurs. Whether there
is some form of genetic selection for brighter colors in more northern
areas, or if this phenomenon is simply a response to local environmental
conditions (water temperature or amount of daylight) is not clear. For
most species, the more northern stocks express this color variation as
a simple intensification of the generic pattern, with most areas of the
body showing brighter hues of the characteristic species colors. For spawning
chum salmon in the northern portion of their range, the result is often
brighter maroons or reds in the banding pattern, darker and more extensive
blacks on ventral surfaces and on the ventral and anal fins, and generally
more colorful heads and body ground colors.
The chinook salmon is an exception
to the above tendency; there is actually a shift in the basic spawner
colors in stocks along the coast. In California and coastal Oregon, chinook
spawners display a dark brown or blackish color. In Washington, the typical
spawning chinook will be a lighter olive brown, and in the Puget Sound
region, an occasional dark red spawner will be seen. Proceeding north
of Washington State, chinook spawners become progressively redder, until
bright red spawners are the rule, as in Alaska..
3. Stock Differences
Individual populations, or stocks, of salmon can display color patterns
distinctly different from adjacent populations. A stock of fish is generally
defined as a discrete group that is reproductively isolated from other
populations; in other words, no significant interchange of spawners occurs
among populations. This reproductive isolation allows a stock to adapt
to local conditions, which can result in changes in run riming, survivals,
body forms, color patterns, etc. In the case of color patterns, stock
differences are often related to latitudinal differences, because different
stocks are encountered along the Pacific coast.
There are, however, examples
of color differences in stocks of salmon that occupy the same region.
Puget Sound chum salmon have developed three distinct times for spawning:
summer, fall, and winter stocks. A general observation is that the summer
stocks, those spawning in September and October, often exhibit brighter
spawning colors than their fall and winter spawning counterparts. A similar
example of brighter spawning colors in early run stocks can be seen in
steelhead in the giant west coast river systems like the Columbia and
Skeena rivers. Early run, upriver steelhead stocks generally display distinctly
brighter (redder) spawning colors than the later run winter steelhead
spawning in lower river tributaries. Whether these examples of color variations
between differently timed stocks represent genetically determined traits,
or are just a response to local environmental conditions (different water
temperatures or ambient light levels) is unclear. It is certain, however,
that heritable traits, like color patterns, can vary in reproductively
4. Social & Sexual Differences
To throughly appreciate the spawning life history of Pacific salmon, an
understanding of how and when male and female fish express various color
patterns is necessary. All species of Pacific salmon display a similar
set of color patterns which represents a non-verbal language that contributes
to the individual's success in attracting potential mates and in repelling
The general color
patterns evident in spawning Pacific salmon are vertical bars in males,
and a single dark horizontal stripe in females. While spawning females
of all species display some variation of the stripe pattern, the dominant
males of different species express the barred pattern to varying degrees.
The barred pattern in males varies from the bold bars of the chum spawner
to a more subtle, vertical pattern of mottling in species with a darker
body color (e.g. chinook and coho), and some individual fish show no obvious
bars. Subdominant males, those individuals that have not successfully
competed for and attracted mates, tend to reverse the pattern by displaying
a stripe. Spawning color patterns are displayed most distinctly by chum
salmon, which makes that species an excellent example for describing the
characteristics of spawning colorations. The following descriptions of
the color patterns of spawning chum salmon are from a study by Steve Schroder,
who observed fall-run fish in Big Beef Creek, a stream entering Puget
Sound in Washington.
chum salmon moving upstream to spawn usually display a subdominant
stripe pattern. This reduces individual aggression and helps the
fish save needed energy reserves (they have stopped feeding). It
also allows them to school in secure stream areas, lowering losses
chum salmon above displaying the horizontal stripe that reduces
the amount of aggression that she is subjected to and communicates
her femininity to prospective mates. The stripe pattern usually
starts with a dark blotch on the operculum, and may extend through
the center portion of the caudal fin.
|© 2000 Steve
anesthetized female chum spawner above showing the bar color pattern,
which is totally different from the lateral striped pattern of a
live, spawning female. If you compare the photo of this female churn
with the underwater photograph of the striped female spawner above,
it would be easy to incorrectly assume that the two fish were members
of different species.
male chum salmon above displaying the broken stripe pattern. The
black color is present in those portions of the stripe that overlay
the suppressed vertical bar pattern. The dorsal mottling on this
fish is in large part caused by sunlight penetrating the riffled
|© 2000 Steve
male chum spawner above showing the bar color pattern. The reddish-purple
bars are places in the widest part of the fish to enhance the apparent
In chum salmon the bar color
pattern consists of black and red streaks that run perpendicular to the
length of the fish. From the posterior edge of the operculum to the tip
of the pectoral fins the bars are black. From this point to the posterior
edge of the ventral fins (the widest part of the fish), the bars are a
reddish-purple after which they become black again. They overlie a mottled
green-yellow background which becomes tan on the dorsal surface of the
peduncle. The stripe pattern consist of a single black purple band that
runs parallel to the length of the fish. Sometimes a fine white band borders
the top and bottom of the stripe which tends to further enhance it. This
stripe covers approximately thirty percent of the lateral surface area
of the fish. Both sexes are able to quickly change (within seconds) from
one pattern to the other, although females usually maintain the stripe
There are various
intermediate color stages between the bars of a dominant male and the
stripe pattern of a spawning female. These intermediate patterns will
often be expressed by subdominant and stressed fish (see photo of frightened
chum below). The pattern is usually a partial stripe overlying a subdued
banding pattern. The result is a broken stripe with the black color displayed
only over areas that would normally be a part of the band pattern. Females
often totally suppress the banding pattern, leaving only the broken stripe.
of chum salmon to rapidly shift from one basic color pattern to another
is apparently the result of several selection pressures. In spawning
populations of chum salmon it pays females to advertise their femininity
since that will simultaneously reduce the amount of aggression they
are subjected to and enhance their attractiveness to males. Males are
also expected to develop masculine traits that repulse or threaten rival
and attract females. To the human eye, and most likely to all vertebrate
eyes, bars that run perpendicular to the long axis of an object tend
to magnify its apparent width while those running parallel to the long
axis appear to reduce its bulk. The bar color pattern thus enhances
the presumed size of a male to his rivals and prospective mates.
Kees Groot, a Canadian scientist,
discovered that a male chum salmon's social position relative to other
adjacent rivals is reflected by his color pattern. Groot placed adult
chum salmon into an aquarium and allowed the fish to form pairs, complete
with satellite males (subdominant males that lie downstream from a pair).
He observed that the satellite males and females had the stripe color
pattern while the dominant males all possessed the bar pattern. Moreover,
Groot was able to quickly (within seconds) alter the color pattern of
the dominant male by striking its side with a broom handle. Invariably,
the struck male lost its vertical bars and developed a dark lateral stripe.
Once the broom handle was removed, the dominant male would usually nip
at adjacent satellite males and in the process resume the bar color pattern.
Hundreds of observations made in an experimental stream by Schroder corroborated
Groot's finding that dominant chum salmon males typically possess the
bar color pattern. He found for instance, that dominant males usually
had the bar color pattern and that satellite males almost always had a
single dark stripe.
such as chum salmon where competition for females is often intense,
males are expected to develop alternative reproductive strategies. Because
satellite males almost always have the stripe pattern and closely resemble
females, the use of this pattern may reflect a type of female mimicry.
Such mimicry commonly occurs in breeding populations of many species
when portions of the male population are denied direct access to females.
In chum salmon, males having the stripe color pattern avoid intense
male aggression and can get close enough to spawning pairs to successfully
steal fertilizations. Females often attack such males and slow down
their reproductive behavior when courted by them. However, the capacity
to rapidly shift from the bar to stripe pattern clearly enhances a male's
ability to fertilize eggs.
A visit to a spawning stream
is necessary to observe this important nonverbal form of communication.
A typical grouping of spawning salmon that would likely be observed would
include a striped female on a spawning nest, flanked by a large heavily
barred dominant male. Downstream of this pair might be one or two subdominant
satellite males displaying variations of the stripe pattern. These satellite
males would most likely be on the side of the female opposite of the dominant
male. Further downstream might be another spawning pair, or a number of
subdominant males and females that have yet to select spawning sites or
5. Stressed Fish
Photographs of live sport caught salmon would seem to represent ideal
representations of the color patterns of living salmon. However, there
are several problems with photographs of this type. A disturbed or recently
captured live fish will certainly not display dominant or subdominant
color patterns. As explained earlier, these patterns only develop when
the fish is competing for or spawning with potential mates. A frightened
fish, or one that has been removed from the security of the stream environment,
will default to the generic color pattern for the species, which is usually
subdued in color and may be quite different from the colors displayed
by a free swimming salmon. Another substantial problem is that extra production
of adrenaline and other hormones caused by stress can result in a distinct
lightening of the skin (see photograph below).
|© 2000 Jim
chum salmon. This male chum salmon panicked when exposed to human
scent in the water. In its rush to escape, the fish beached itself
and was thoroughly frightened. The light body color is probably
the result of an adrenaline surge, producing a general blanching
of skin color.
The opposite effect is observed
when a fish is stressed to the point of exhaustion, like the typical sport-caught
fish. In this case, the adrenaline blanching effect is overridden by other
hormones, which disperse pigments in the chromatophores, resulting in
a darkening of ground color on dorsal and other surfaces. In fact, photographs
of live fish commonly show just such a dark skin color, which can be very
different than the color normally exhibited by the fish in the stream.
The above photograph of the
frightened chum salmon shows another interesting feature; a down-turned
eye. A living fish lying on its side will rotate its top eye downward
in the eye socket, and this down-turned eye in a photograph shows that
the fish was still alive. In fact, the fish displaying a down-turned eye
is simply demonstrating an equilibrium reflex by reacting to the unnatural
position of lying on its side. If you hold a live fish on its side and
look at the bottom eye, you will see that it is turned upwards in its
socket because the fish is trying to orient itself to the normal upright
The same photograph also shows
equilibrium responses in fin positioning. The pectoral fin is clamped
tightly against the side, the right ventral fin is curled upwards, and
the dorsal and anal fins are cupped. These are the fin positions that
will return the fish to an upright orientation as soon as it begins moving
forward in the water.
male and female chum spawners showing the subdued colors and dark
dorsal surfaces typical of dead fish. The male (top) has the bar
pattern of a dominant male but lacks the intensity of color of a
live fish. The female also exhibits the generic bar pattern which
is entirely different than the characteristic stripe of a live spawner.
6. Dead Fish
The dead fish photograph is the most common source of information on the
colors of salmon and other fishes. If one wants to truly understand the
color patterns of living salmon as they appear in their natural habitat,
dead fish photographs must be used with caution. When a fish dies, neutral
control of color ends and the fish will typically display subdued generic
colors and often an unnaturally dark body ground color. Dominant and subdominant
colors and patterns typical of spawning fish will be missing. Such photographs
will show the general generic colors, and can be used to identify patterns
of spots and stripes, and to see other fine points like scale detail.
Wild chum salmon are abundant in many western Washington streams,
providing an excellent opportunity to learn about their freshwater life
history through first-hand observation. One of the most intriguing characteristics
of this species is the non-verbal language of changing color patterns
used by chum salmon during competition for mates and the subsequent spawning
process. To gain insight into the significance of the fascinating variations
that occur in salmon colors and patterns, there are few good substitutes
for sitting on the bank of a stream, observing living fish actually engaged
in the spawning process. It is also a pretty nice way to spend your time
on a sunny fall day.
Ames, J. and S. Schroder. 1995. Color variations in spawning Pacific
salmon. Breakthrough Magazine. No 41. p. 76-83.
Schroder, S. L. 1981. The
role of sexual selection in determining overall mating patterns and mate-choice
in chum salmon. Ph.D. thesis, Univ. Wash., Seattle, 274 p.