Coloration

Fishes are among the world's most colorful inhabitants. A large
number of teleost fishes are brightly and brilliantly colored, while
some are of more uniform and sober shade. The coloration or
patterns of fish may reveal information about its life style and
ecosystem and has a functional significance. Generally, the fishes
are darker on their upper surfaces due to sunlight while the ventral
and lateral sides are relatively lighter in coloration.
Source of color
Coloration in fishes is attributed to the presence of two kinds of
special cells, chromatophores and iridocytes. The chromatophores
are branched connective tissue cells located in the dermis either
above or below the scales. Chromatophores contain pigments
of various kinds of pigment granules which may be carotenoids
(yellow - red), melanin (black), flavins (yellow), purines (white or
silvery), pterins, porphyrins and bile pigments. Based upon the
color of the pigments, the chromatophores are of the following
types:
a. Melanophores
The pigmentary material of melanophore is black colored, called
as melanin. It is formed from an amino acid tyrosine, which is
converted into melanin in the presence of copper containing
Introductory Ichthyology
enzymes tyrosine melanin, so formed, associates with the
cytoplasmic organ all called the melanosome. A brown in black
pigment called ‘eumelanin’ is also sometimes found within the
melanophores.
b. Iridophores
The pigmentary material in these cells is guanine. Guanine is
opaque, whitish or silvery. It is a waste product and is deposited
in the form of granules. These granules are opaque and posses
great reflecting power, so that the iridocytes may also be called
the ‘mirror cells’. Tiny crystal of this pigment produces a
white or silvery white apperance and against a background of
melanophores, imparts a blue color to the fish.
c. Xanthrophores and erythrophores
The pigmentary materials of these cells include carotenoids and
pterins. They are white, yellow, orange or red colored pigments,
which are abundantly found in plants but the fishes are incapable
to synthesize them, hence they depend upon the plants for a
dietary supply of the pigmentary material. The cellular organelle
containing pteridines are known as pterinosome and the ultramicroscope
vesicles of cells containing carotenoid are called the
carotenoid vesicles.

Mixed coloration in fish

Color patterns of a majority of a fishes are due to the combined
effects of chromatophores containing different kinds of pigmentary
granules. For example, the black and yellow chromatophores
together develop green color. Likewise, yellow and black or orange
and blue may combine separately to give brown appearance to the
fish. Similarly, yellow mixed with black gives brown or blackish
coloration in fishes.Color change in fish
Various species of fish change the pattern of their coloration in
accordance to their surroundings or in relation to the phases of
their behavior. These changes in appearance are under the control
of chromatophores.Significance of coloration
Coloration is important, not only for look, but for survival. The
coloration in fishes performes many adaptive functions and
is useful to the fish in a variety of ways such as camouflage,
concealment and disguise, aggressive purpose, courting patterns,
warning pattern, etc.