CHAPTER XIII 



THE COLORS OF FISHES 



IGMENTATION. — The colors of fishes are in general pro- 

 duced 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 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 Avater itself or like the bottom below it. To 

 fishes in search of prey from below, the bell}' 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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