is an examplary pattern of animal coloration in which an animal’s pigmentation
is darker on the upper side and lighter on the under side of the body. When light
falls on any volume uniformly
colored object from
above, it makes the upper side appear lighter and the under side darker with
the gradual transition between them. Thanks to the counetrshading with the dark
upper side and the light under side, the same object appears flat and thus invisible on the surrounding background.
This basic pattern
is found in many species of mammals, reptiles, birds, fish and other animals.
countershading is determined by color vision of fish that is characterized by the different bell like curves of spectral
sensitivity. Spectral sensitivity
is an ability of the eye to perceive monochromatic light of equal power with the different wavelengths. Eyes of saltwater fish, and human, are most
sensitive to light with the wavelengths
of 550-560 nm (the green-yellow part
of the spectrum). Because fresh waters are optically turbid, eyes of freshwater
fish are more sensitive to light with the wavelengths of 600-680 nm (the orange-red
part of the spectrum). Due to bell like dependence of spectral sensitivity equipower
monochromatic light of different
wavelengths are not equally bright to
the eye. Green light is most bright for human and saltwter fish, red light is most
brigth for freshwater fish contrary to our perception.
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Red displacement of spectral
sensitivity in freshwater fish
the terms of cryptic countershading, coloration of freshwater fish may be
conditionally divided into achromatic, or bright countershading patterns and
chromatic, or color countershading patterns. Greyish back, silver (mirrored)
sides and whitish belly are typical for fish with the achromatic
countershading. Green, yellow (goldish or golden), orange and red colors are
main components of the color countershading patterns. Darker colors lie on the top, brighter colors
lie on the bottom with the corresponding gradual transitions. The first sign of
the presence of color countershading in an appearance of freshwater fish is red
color of pectoral, pelvic, anal and caudal fins lied in the less illuminated parts or in
the shadow of the fish’s body.
In general, coloration of freshwater pelagic fish is ranged from
blank achromatic countershading patterns to color countershading patterns,
depending on the optical properties of the water.
idealized mixed countershading patterns, greenish back, silver sides, whitish
belly as well as yellowish, orange, reddish or red pectoral, pelvic, anal and caudal fins are typical. This
type of coloration is found in European asp, Aspius aspius, Aral redlip, A.a.
taeniatus, in many Amur fish (see Nikolski, 1956) like Amur redfin, Pseudaspius leptocephalus, skygazer, Erythroculter erythropterus, Mongolian
redfin, E. mongolicus, yellowcheek, Elopichthys bambusa, three-lip, Opsariichthys uncirostris amurensis, and
in many other freshwater pelagic fish in other regions. Note, yelllow golden
color of gill covers and yellow color of the lower lip in the yellowcheeks is
in the full conformity with the theory of color countershading in fresh waters.
general, the colored lower fins are practically absent in pelagic fish with the
wedge like shadowless body (Aleyev, 1975) and occur in pelagic fish with the
roundish shadow made body.
color countershading patterns with greenish back, silver sides, whitish belly
and the colored lower fins are ultimately developed in frshwater littoral fish.
Such generally known fish as roach, Rutilus
rutilus, rudd, Scardinius
erythrophthalmus, ide, Leuciscus idus,
chub, L. cephalus, and many other are
classic examples. In contrast to pelagic fish in which coloration of the lower
fins may be missing, in littoral fish this feature is constant and exptremely
littoral zones are commonly represented by open deep areas and overgrown
shallow areas, with the significantly different optical properties of the water
in these areas. In overgrown shallow areas, floating aquatic plants (like water
lily and other) and submerged aqauatic plants work as optical filters and
reflectors. Moreover, the water in these areas contains more organic substances
than the water in open areas. Thanks to the coaction of these two factors, the water as the optical medium is enriched in overgrown areas
by rays in the green-yellow part of the spectrum. In
these optical conditions, roach, rudd, ide and other fish have more or less
distinct golden sides instead of silver ones and yellowish or even orangish
belly instead of whitish one.
olive golden sides is found in freshwater fish, like tench, Tinca tinca, that constantly live in the overgrown areas.
According to calculations (Johnsen, 2003; Johnsen & Sosik, 2003), in the described optical
conditions colored diffusely reflective surfaces are more cryptic than mirrored
directionally reflective ones.
in freshwater littoral fish with the high flattened body, like bream, Abramis brama, coloration of the lower
fins is absent or less developed. In addition, deep dwelling bream, A. brama, have golden sides versus
silver ones and yellowish or orangish belly versus whitish one.
addition, there are wild gene based golden color morphs of cyprinid
fish (such as carp, rudd, ide, tench and more: for example, see Kvasnička
et al., 1998).
In freashwater fish with the so called phytophilous coloration, mixed color countershading
patterns with greenish back, silver greenish or golden greenish sides, whitish
belly and yellowish, orange, reddish or red fins are basic. At the same time,
coloration of sides in these fish is supplemented with the achromatic or
chromatic spots, irregularities and transverse bands that form the so called
disruptive patterns cryptic on the background of underwater plants and woods.
Phytophilous colorations with the various disruptive patterns are found in many freshwater
fish worldwide. Examples are generally known pike Esocidae, except Amur pike, Esox reicherti, with the rheophilous
cryptic patterns (Nikolski, 1956), freshwater perch Percidae, such as Perca fluviatilis and P. flavescens, piranha Characidae, sunfish
Centrarchidae like largemouth bass, Micropterus
salmoides, bluegill, Lepomis
macrochirus, and many other fish. Furthermore, bellies in these fish are
frequently yellowish, orangish and reddish outside the breeding season.
color countershading patterns with greenish back, silver or golden sides,
whitish or yellowish belly and yellowish, orangish or reddish fins are basic in
fish with the so called rheophilous, or brook coloration. In these fish, basic countershading
coloration is supplemented with the numerous achromatic (black) and chromatic (orange,
red) dots, simple and ringed, that cover usually all the upper part of the body,
the head and the upper fins. Such well known freshwater fish as brown trout, Salmo trutta, European grayling, Thymallus thymallus, taimen, Hucho taimen, and
many other are typical examples. With color countershading and dots, the
rheophilous fish are cryptic in murmuring streams and on the background of
mottled stony bottom with
flecks of sunlight from the surface waves. In addition to dots as elements of the
rheophillous coloration, young individuals of these fish, called parr, have on
their sides per an ordered lateral row of large spots that are basic elements
of the so called lithophilous coloration.
Graylings have the less dotty body
than other rheophilous freshwater fish, but they have huge rainbow-patchy
dorsal fins with an evident cryptic function. According to Darchambeau &
Ponchin (1997), brightly colored dorsal fins play an important role in the spawning behaviour of these fish.
In sum, an idealized
coloration of fish consists of cryptic patterns of two types, achromatic and
chromatic countershading, and disruptive patterns of three types: phytophilous, rheophilous, lithophilous. The so called
psammophilous (sandy) pattern and some other patterns are not considered here. By
definition (Endler, 2006), disruptive patterns are conspicuous, because they
must dismember an appearance of an animal into the disconnected parts. Taken
together, however, cryptic and disruptive patterns create an overall camouflage coloration in which, in addition, some
elements may be used as signals in intraspecific and interspecific
Y.G. 1976. Nekton. Naukova Dumka Publishers, Kyiv
F., Ponchin P. 1997. Field observations of the spawning
behaviour of European grayling. Journal of Fish
Biology 51, 1066-1068
2006. Disruptive and cryptic coloration. Proceedings
of the Royal Society, Biological Scienses 273, 2425-2426
P., Flajšhans M., Ráb P., Linhart O. 1998. Inheritance
studies of blue and golden varieties of tench (Pisces: Tinca tinca L.). Journal of
Heredity 89, 553-556
2003. Lifting the cloak of invisibility: the effects of changing optical
conditions on pelagic crypsis. Integrative
an Comparative Biology 43, 580-590
Johnsen S., Sosik
H.M. 2003. Cryptic
coloration and mirrored
sides as camouflage
strategies in near-surface pelagic habitats: Implications for foraging and
predator avoidance. Limnology and Oceanography 48, 1277-1288
G.V. 1956. Fishes of the Amur basin. USSR
Academy of Science Publishing, Moscow