CHAPTER VI 
THE COLORS OF FISHES 
¥ IIGMENTATION.—The colors of fishes are in general pro- 
duced by oil sacs or pigment cells beneath the epidermis 
ec’ i=) or in some cases beneath the scales. Certain metallic 
ades, 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 inter- 
ference 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. 
In the open seas, where the water seems very blue, blue 
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