THE ALBINO BROOK TROUT. 3OI 



Shade. — Fish in water that is densely shaded are darker than those living in 

 the open under similar conditions. 



The breeding season produces periods of changes in color. 



The amount of food and kind of food are said to produce changes in the 

 color of the fish. 



Certain waters seem to be particularly adapted for trout, and in some waters a 

 large number of minute hydra exist which is thought to produce a greater number 

 and more intense coloring of the small red spots on the sides' of the fish. 



These changes are accounted for by an increase or decrease of the black, red, 

 and yellow pigment cells or chromatophores in the skin of the fish; or by rapid 

 contraction or expansion of the chromatophores which happen to be developed. 

 Black chromatophores predominate in a fish which lives in deep water on a black 

 bottom. This is an example of the melanic form. Fish that live in shallow 

 water with light-colored bottom have the pale chromatophores predominating. 

 These differences in depth of water, shade, and nature of the bottom would have 

 no effect in producing changes in the color of albinos, as they have no chromato- 

 phores. 



An ordinary fish can be changed in color by an experiment in an aquarium. 

 If the light coming from above, to an aquarium, is cut off and all light is admitted 

 from below, thus reversing the usual direction of the light ray, the fish will 

 become light on the back and dark on the belly. This would seem to indicate 

 that the color of fish is due in part to the direct effects of light, a fact 

 which has been denied. The different colors of fish are produced by different colors 

 of pigment in their skin, the same as different races of people are distinguished by 

 the different colors of their pigments. Many fish living in caves, but not all, have 

 lost their color and become white and limpid; but in the deep sea, where no light 

 comes, the fish are said to be usually pearly or black. 



Dr. Gunther, in his book "Introduction to the Study of Fish," says: "Total 

 absence of chromatophores in the skin, or albinism, is very rare among fish; 

 much more common is incipient albinism in which the dark chromatophores 

 are changed into cells with a more or less intense yellow pigment. Fishes in a state 

 of domestication, like the Crucian carp of China, the carp, the tench, and the ide, 

 are particularly subject to this abnormal coloration and are known as the common 

 gold fish, the gold tench and the gold orfe. But it occurs also, not rarely, in fishes in 

 a wild state and has been observed in haddock, flounders, carp, roach and eels. The 

 amount of variation is greater in fish than in any of the higher class of vertebrates. 

 Greater in some families than in others Naturally greater in the few species 

 which have been domesticated." 



