THE COLORS OF FISHES. 
DAVID STARR JORDAN. 
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 stria- 
tions 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 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 closer 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 uniformly colored. 
In the open seas, where the water seems very blue, blue 
colors, and especially metallic shades, take the place of olivace- 
ous gray or green. As we descend into deep water, especially 
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