THE COLORS OF FISHES
=Pigmentation.=--The colors of fishes are in general produced by oil
sacs or pigment cells beneath the epidermis or in some cases beneath
the scales. Certain metallic shades, silvery blue or iridescent,
are produced, not by actual pigment, but, as among insects, by the
deflection of light from the polished skin or the striated surfaces
of the scales. Certain fine striations give an iridescent appearance
through the interference of light.
The pigmentary colors may be divided into two general classes, ground
coloration and ornamentation or markings. Of these the ground color is
most subject to individual or local variation, although usually within
narrow limits, while the markings are more subject to change with age
or sex. On the other hand, they are more distinctive of the species
itself.
=Protective Coloration.=--The ground coloration most usual among
fishes is protective in its nature. In a majority of fishes the back
is olivaceous or gray, either plain or mottled, and the belly white.
To birds looking down into the water, the back is colored like the
water itself or like the bottom below it. To fishes in search of prey
from below, the belly is colored like the surface of the water or the
atmosphere above it. In any case the darker colored upper surface casts
its shadow over the paler lower parts.
In shallow waters or in rivers the bottom is not uniformly colored.
The fish, especially if it be one which swims close to the bottom, is
better protected if the olivaceous surface is marked by darker cross
streaks and blotches. These give the fish a color resemblance to the
weeds about it or to the sand and stones on which it lies. As a rule,
no fish which lies on the bottom is ever quite uniformly colored.
[Illustration: FIG. 167.--Garibaldi (scarlet in color), _Hypsypops
rubicunda_ (Girard). La Jolla, San Diego, California.]
In the open seas, where the water seems very blue, blue colors, and
especially metallic shades, take the place of olivaceous gray or green.
As we descend into deep water, especially in the warm seas, red pigment
takes the place of olive. At a moderate depth a large percentage of
the fishes are of various shades of red. Several of the large groupers
of the West Indies are represented by two color forms, a shore form
in which the prevailing shade is olive-green, and a deeper-water
form which is crimson. In several cases an intermediate-color form
also exists which is lemon-yellow. On the coast of California is a
band-shaped blenny (_Apodichthys flavidus_) which appears in three
colors, according to its surroundings, blood-red, grass-green, and
olive-yellow. The red coloration is also essentially protective, for
the region inhabited by such forms is the zone of the rose-red algæ.
In the arctic waters, and in lakes where rose-red algæ are not found,
the red-ground coloration is almost unknown, although red may appear
in markings or in nuptial colors. It is possible that the red, both of
fishes and algæ, in deeper water is related to the effect of water on
the waves of light, but whether this should make fishes red or violet
has never been clearly understood. It is true also that where the red
in fishes ceases violet-black begins.
In the greater depths, from 500 to 4000 fathoms, the ground color in
most fishes becomes deep black or violet-black, sometimes with silvery
luster reflected from the scales, but more usually dull and lusterless.
This shade may be also protective. In these depths the sun's rays
scarcely penetrate, and the fish and the water are of the same apparent
shade, for black coloration is here the mere absence of light.
In general, the markings of various sorts grow less distinct with the
increase of depth. Bright-red fishes of the depths are usually uniform
red. The violet-black fishes of the oceanic abysses show no markings
whatever (luminous glands excepted), and in deep waters there are no
nuptial or sexual differences in color.
Ground colors other than olive-green, gray, brown, or silvery rarely
appear among fresh-water fishes. Marine fishes in the tropics sometimes
show as ground color bright blue, grass-green, crimson, orange-yellow,
or black; but these showy colors are almost confined to fishes of the
coral reefs, where they are often associated with elaborate systems of
markings.
=Protective Markings.=--The markings of fishes are of almost every
conceivable character. They may be roughly grouped as protective
coloration, sexual coloration, nuptial coloration, recognition colors,
and ornamentation, if we may use the latter term for brilliant hues
which serve no obvious purpose to the fish itself.
Examples of protective markings may be seen everywhere. The flounder
which lies on the sand has its upper surface covered with sand-like
blotches, and these again will vary according to the kind of sand it
imitates. It may be true sand or crushed coral or the detritus of lava,
in any case perfectly imitated.
Equally closely will the markings on a fish correspond with rock
surroundings. With granite rocks we find an elaborate series of
granitic markings, with coral rocks another series of shades, and if
red corals be present, red shades of like appearance are found on the
fish. Still another kind of mark indicates rock pools lined with the
red calcareous algæ called corallina. Black species are found in lava
masses, grass-green ones among the fronds of ulva, and olive-green
among Sargassum or fucus, the markings and often the form corresponding
to the nature of the algæ in which the species makes its home.
[Illustration: FIG. 168.--Gofu, or Poison Fish, _Synanceia verrucosa_
(Linnæus). Family _Scorpænidæ_. Specimen from Apia, Samoa, showing
resemblance to coral masses, in the clefts of which it lives.]
=Sexual Coloration.=--In many groups of fishes the sexes are
differently colored. In some cases bright-red, blue, or black markings
characterize the male, the female having similar marks, but less
distinct, and the bright colors replaced by olive, brown, or gray. In a
few cases, however, the female has marks of a totally different nature,
and scarcely less bright than those of the male.
[Illustration: FIG. 169.--Lizard-skipper, _Alticus saliens_ (Forster).
A blenny which lies out of water on lava-rocks, leaping from one to
another with great agility. From nature; specimen from Point Distress,
Tutuila Island, Samoa. (About one-half size.)]
=Nuptial Coloration.=--Nuptial colors are those which appear on the
male in the breeding season only, the pigment afterwards vanishing,
leaving the sexes essentially alike. Such colors are found on most of
the minnows and dace (_Cyprinidæ_) of the rivers and to a less degree
in some other fresh-water fishes, as the darters (_Etheostominæ_) and
the trout. In the minnows of many species the male in spring has
the skin charged with bright pigment, red, black, or bright silvery,
for the most part, the black most often on the head, the red on the
head and body, and the silvery on the tips of the fins. At the same
time other markings are intensified, and in many species the head and
sometimes the body and fins are covered with warty excrescences. These
shades are most distinct on the most vigorous males, and disappear with
the warty excrescences after the fertilization of the eggs.
[Illustration: FIG. 170.--Blue-breasted Darter, _Etheostoma camurum_
(Cope), the most brilliantly colored of American river-fishes.
Cumberland Gap, Tennessee.]
Nuptial colors do not often appear among marine fishes, and in but few
families are the sexes distinguishable by differences in coloration.
=Recognition-marks.=--Under the head of "recognition-marks" may be
grouped a great variety of special markings, which may be conceived to
aid the representatives of a given species to recognize each other.
That they actually serve this purpose is a matter of theory, but the
theory is plausible, and these markings have much in common with the
white tail feathers, scarlet crests, colored wing patches, and other
markings regarded as recognition-marks among birds.
Among these are ocelli, black- or blue-ringed with white or yellow,
on various parts of the body; black spots on the dorsal fin; black
spots below or behind the eye; black, red, blue, or yellow spots
variously placed; cross-bars of red or black or green, with or without
pale edges; a blood-red fin or a fin of shining blue among pale ones;
a white edge to the tail; a yellow, blue, or red streamer to the
dorsal fin, a black tip to the pectoral or ventral; a hidden spot
of emerald in the mouth or in the axil; an almost endless variety
of sharply defined markings, not directly protective, which serve
as recognition-marks, if not to the fish itself, certainly to the
naturalist who studies it.
These marks shade off into an equally great variety for which we can
devise no better name than "ornamentation." Some fishes are simply
covered with brilliant spots or bars or reticulations, their nature
and variety baffling description, while no useful purpose seems to be
served by them, unless we stretch still more widely the convenient
theory of recognition-marks.
In many cases the markings change with age, certain bands, stripes, or
ocelli being characteristic of the young and gradually disappearing.
In such cases the same marks will be found permanent in some related
species of less differentiated coloration. In such cases it is safe to
regard them as ancestral.
In case of markings on the fins and of elaborate ornamentation
in general, it is best defined in the oldest and most vigorous
individuals, becoming intensified by degrees. The most brilliantly
colored fishes are found about the coral reefs. Here may be found
species of which the ground color is the most intense blue, others
are crimson, grass-green, lemon-yellow, jet-black, and each with a
great variety of contrasted markings. The frontispiece of this volume
shows a series of such fishes drawn from nature from specimens taken
in pools of the great coral reef of Apia in Samoa. These colors are
not protective. The coral masses are mostly plain gray, and the fishes
which lie on the bottom are plain gray also. Nothing could be more
brilliant or varied than the hues of the free-swimming fishes. What
their cause or purpose may be, it is impossible to say. It is certain
that their intense activity and the ease with which they can seek
shelter in the coral masses enable them to defy their enemies. Nature
seems to riot in bright colors where her creatures are not destroyed by
their presence.
=Intensity of Coloration.=--In general, coloration is most intense
and varied in certain families of the tropical shores, and especially
about coral reefs. But in brilliancy of individual markings some
fresh-water fishes are scarcely less notable, especially the darters
(_Etheostominæ_) and sunfishes (_Centrarchidæ_) of the streams of
eastern North America. The bright hues of these fresh-water fishes
are, however, more or less concealed in the water by the olivaceous
markings and dark blotches of the upper parts.
[Illustration: FIG. 171.--Snake-eels, _Liuranus semicinctus_ (Lay and
Bennett), and _Chlevastes colubrinus_ (Boddaert), from Riu Kiu Islands,
Japan.]
[Illustration: FIG. 172.--Coral Reef at Apia.]
=Coral-reef Fishes.=--The brilliantly colored fishes of the tropical
reefs seem, as already stated, to have no need of protective
coloration. They save themselves from their enemies in most cases by
excessive alertness and activity (_Chætodon_, _Pomacentrus_), or else
by busying themselves in coral sand (_Julis gaimard_), a habit more
frequent than has been suspected. Every large mass of branching coral
is full of lurking fishes, some of them often most brilliantly colored.
=Fading of Pigments in Spirits.=--In the preservation of specimens most
red and blue pigments fade to whitish, and it requires considerable
care to interpret the traces which may be left of red bands or blue
markings. Yet some blue pigments are absolutely permanent, and
occasionally blood-red pigments persist through all conditions. Black
pigment seldom changes in spirits, and olivaceous markings simply fade
a little without material alteration. It is an important part of the
work of the systematic ichthyologist to learn to interpret the traces
of the faded pigment left on specimens he may have occasion to examine.
In such cases it is more important to trace the markings than to
restore the ground color, as the ground color is at once more variable
with individuals and more constant in large groups.
=Variation in Pattern.=--Occasionally, however, a species is found in
which, other characters being constant, both ground color and markings
are subject to a remarkable range of variation. In such cases the
actual unity of the species is open to serious question. The most
remarkable case of such variation known is found in a West Indian fish,
the vaca, which bears the incongruous name of _Hypoplectrus unicolor_.
In the typical vaca the body is orange with black marks and blue lines,
the fins checkered with orange and blue. In a second form the body
is violet, barred with black, the head with blue spots and bands. In
another form the blue on the head is wanting. In still another the body
is yellow and black, with blue on the head only. In others the fins
are plain orange, without checks, and the body yellow, with or without
blue stripes and spots, and sometimes with spots of black or violet.
In still others the body may be pink or brown, or violet-black, the
fins all yellow, part black or all black. Finally, there are forms deep
indigo-blue in color everywhere, with cross bands of indigo-black, and
these again may have bars of deeper blue on the head or may lack these
altogether. I find, no difference among these fishes except in color,
and no way of accounting for the differences in this regard.
Certain species of puffer (_Tetraodon setosus_, of Panama, and
_Tetraodon nigropunctatus_, of Polynesia) show similar remarkable
variations, being dark gray with white spots, but varying to
indigo-blue, lemon-yellow, or sometimes having coarse blotches of
either. Lemon-yellow varieties of several species are known, and
these may be due to a failure of pigment, a sort of semi-albinism.
True albinos, individuals wholly without pigment, are rare among
fishes. In some cases the markings, commonly black, will be replaced
by a deep crimson which does not fade in alcohol. This change happens
most frequently among the _Scorpænidæ_. An example of this is shown
in the frontispiece of Volume II of this work. The Japanese okose or
poison-fish (_Inimicus_) is black and gray about lava-rocks. In deeper
water among red algæ it is bright crimson, the color not fading in
spirits, the markings remaining the same. In still deeper water it is
lemon-yellow.