The Colors of Fishes 235 



hues of these fresh-water fishes are, however, more or less con- 

 cealed in the water by the olivaceous markings and dark blotches 

 of the upper parts. 



Coral-reef Fishes. The brilliantly colored fishes of the trop- 

 ical reefs seem, as already stated, to have no need of pro- 

 tective coloration. They save themselves from their enemies 

 in most cases by excessive alertness and activity (Chatodon, 

 Pomacentrus) , or else by burying themselves in coral sand (Julis 

 ga-imard), a habit more frequent than has been suspected. 

 Every large mass of branching coral is full of lurking fishes, 

 some of them often most brilliantly colored. 



Fading of Pigments in Spirits. In the preservation of speci- 

 mens most red and blue pigments fade to whitish, and it requires 

 considerable care to interpret the traces which may be left of 

 red bands or blue markings. Yet some blue pigments are abso- 

 lutely permanent, and occasionally blood-red pigments persist 

 through all conditions. Black pigment seldom changes in 

 spirits, and olivaceous markings simply fade a little without 

 material alteration. It is an important part of the work of the 

 systematic ichthyologist to learn to interpret the traces of the 

 faded pigment left on specimens he may have occasion to ex- 

 amine. In such cases it is more important to trace the mark- 

 ings than to restore the ground color, as the ground color is 

 at once more variable with individuals and more constant in 

 large groups. 



Variation in Pattern. Occasionally, however, a species is 

 found in which, other characters being constant, both ground 

 color and markings are subject to a remarkable range of varia- 

 tion. In such cases the actual unity of the species is open to 

 serious question. The most remarkable case of such variation 

 known is found in a West Indian fish, the vaca, which bears 

 the incongruous name of Hypoplectrus unicolor. In the typical 

 vaca the body is orange with black marks and blue lines, the 

 fins checkered with orange and blue. In a second form the 

 body is violet, barred with black, the head with blue spots and 

 bands. In another form the blue on the head is wanting. In 

 still another the body is yellow and black, with blue on the 

 head only. In others the fins are plain orange, without checks, 

 and the body yellow, with or without blue stripes and spots, and 



