. COLORATION 219 



had been polluted with white china clay. Dr. Day has 

 described two lochs in Inverness-shire which were both stocked 

 at the same time with Trout from Loch Morar. The larger 

 of the two, with a sandy and weedy bottom, had the effect 

 after a few years of changing the fish into forms with golden 

 sides and covered with numerous red spots, and with white 

 flesh. In the smaller, where the water was dark coloured and 

 the bottom rocky, the fish developed nearly black heads, 

 yellowish-olive sides, comparatively few black and red spots 

 on each side, and the flesh became pink. Numerous other cases 

 of a similar nature might be described, but the above should 

 suffice to show that the coloration may undergo a definite 

 change in order to harmonise with the surroundings, and that 

 these changes are connected particularly with the amount of 

 light available and the nature of the bottom. Further, there is 

 evidence to suggest that, in some cases at least, the nature of 

 the food may have its eflfect on the colour of the fish. 



Similar changes have been produced under artificial con- 

 ditions, and Sticklebacks kept in glass dishes with a background 

 of black and white tiles have shown considerable variation in 

 colour, those on the white tiles tending to become partially 

 bleached, while those on the black more or less retained their 

 normal coloration. If only exposed to the white tiles for a 

 few days they tend to regain the original colour when put back 

 on the black, but prolonged exposure extending over a period 

 of weeks seems to make the pale colour more or less permanent. 

 Minnows {Phoxinus) kept for experimental purposes in a white 

 porcelain sink will also assume a bleached condition which 

 matches the background, and anglers will sometimes paint the 

 interior of their minnow-can white, so that the bait will assume 

 a lighter colour and thus be more conspicuous to Pike and 

 Perch in deeper and dark water. 



The colour changes in Trout just described are generally 

 slow, but in some fishes they may be practically instantaneous. 

 Most of the tropical Sea Perches {Epinephelus) , for example, are 

 capable of changing in a moment from black to white, yellow 

 to scarlet, red to dull green or dark brown, and can equally 

 readily switch on, as it were, a series of spots, blotches, bars or 

 stripes. The ability of these and other fishes to assume half a 

 dozen diflferent liveries within the space of a few moments is 

 amazing, and the Sea Perches and other forms from Bermuda 

 exhibited in the tanks of the aquarium at New York are a 

 source of constant interest to visitors on account of their 



