COLORATION 221 



covered with little white pebbles the red spots are said to 

 become white to match the altered surroundings. The Turbot 

 [Rhombus) living on dirty mud or sand on the sea bottom is a 

 dull-greyish fish, but in an aquarium tank with sanded floor it 

 is of a pale yellowish hue, and if placed on a background of 

 coarse gravel, yellowish spots are developed over the head and 

 body, separated from one another by a dark network. 



Some experiments conducted at the aquarium at Naples on a 

 Mediterranean Flounder [Bothus) are of interest (PL IIa, b). The 

 same individual was successively placed in glass dishes on the 

 bottom of which were painted chessboard backgrounds of black 

 and white squares, black and white circles, and so on, and was 

 induced to imitate the pattern, but as the background was an 

 unaccustomed one, the colour change took about half an hour 

 instead of the usual second or so. It was found, however, that 

 with practice a fish was soon able to harmonise with the 

 background more rapidly than at first, but its capacity for colour 

 change was limited to the black, brown, grey and white of its 

 ordinary surroundings. An American investigator, experi- 

 menting on Flounders {Paralichthys, etc.), carried the matter 

 further, and found that when placed on loackgrounds of white, 

 black, grey, brown, blue, green, pink, and yellow, they made 

 very good attempts to produce a coloration similar to that on 

 which they were lying. They copied red backgrounds with 

 less accuracy than those of other shades, and whereas yellows 

 and browns were simulated with rapidity, greens and blues 

 took a greater time, and a considerable interval sometimes 

 elapsed before the full eflfect was obtained. 



Although an impulse to conform to the environment is 

 undoubtedly the principal motive for the colour changes of 

 fishes, there are cases in which other factors are involved. 

 Just as we ourselves may undergo a sudden flushing or pallor, 

 certain colour changes of fishes seem to be definitely emotional, 

 and such expressions as "white with fear" and "crimson with 

 rage" assume a literal meaning when applied to some of the 

 " chameleons of the sea." It has been observed that in captivity, 

 under the stress of excitement due to food being thrown into a 

 tank or the artificial light being suddenly turned on, fishes 

 tend to exhibit definite colour phases and markings, and that 

 other "distress phases" are shown by injured or sick individuals, 

 or when the stoppage of the normal flow of water causes actual 

 discomfort to the inhabitants. The very marked colour changes 

 seen in the Bullhead (Cottus) of our own streams and rivers 



