168 MARINE PRODUCTS OF COMMERCE 



the brilliant colors blend fairly well with the coral heads, sea fans, gorgoneans, 

 and other growths. 



Convincing examples of protective coloration occur among flounders. Extensive 

 observations and laboratory tests with species of the genus Paralichthys were 

 carried on over a period of years at the Fish and Wildlife Service Laboratory at 

 Beaufort, N. C. It was found that these flounders not only assumed the color of 

 the bottom on which they lived, but imitated the pattern of the background. If 



(^Courtesy U. S. Fish and Wildlife Service) 



Fig. 10-24. A southern flounder. Photo taken with orthonon plates of 

 specimen adapted to colored backgrounds. Brown background. Note the 

 remarkable simulation of the background in shade and the absence of con- 

 spicuous patterns, especially in Paralichthys. 



placed on blue glass, for example, they took on a definite bluish tinge; if placed on 

 red glass, they became red, and so on. If placed in a white enameled pan with 

 large black spots painted on the bottom, the fish tended to "develop" large dark 

 blotches over the black spots; but if placed in white pans with small black spots, 

 they acquired the small dark spots: Or, if placed on coarse sand and broken shells, 

 they took on a pattern of rather large dark and pale markings, but on fine sand 

 the markings became mere specks. Wild fish were observed many times in nature, 

 especially at night with the use of a strong flashlight. After some experience one 

 learns to look for the outline of a flounder, rather than for the fish itself, as it has 

 so accurately simulated the color and pattern of the bottom on which it lies that 

 it is virtually invisible. There can be little doubt, then, that color affords pro- 

 tection. However, it may serve, also, in an offensive way, for a fish so well 

 "hidden" would scarcely be detected in time by unsuspecting prey (Fig. 10-24). 



The sexes in some species differ in color, the male being the brighter. These 

 differences are sometimes so great that scientists were misled and described the 

 sexes of one species as separate and distinct "species." Furthermore, the colors 

 often change greatly with age. Indeed, fish hatched from eggs, tmlike those born 

 alive, are generally colorless. As a rule they develop color very gradually. The 

 first pigment usually consists of a few dark chromatophores, and in many species 

 the young do not become fully pigmented until they are a couple of inches long. 



