344 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



and is required for safety and concealment. Dr. Stark showed many 

 years ago how suddenly the stickleback au^J other fish changed color 

 when removed from dark pools and placed in white bowls. The change 

 of hue took place with as much rapidity as though it were subject to the 

 caprice of the fish, as is the case with the chameleou. 



Food has. a very decided influence, and in connection with other cir- 

 cumstances will produce a marked effect in the appearance of Salmonidce, 

 even in the same lake. Thus, in Lake Guarda, in Italy, we may observe 

 one specimen with silver sides, blue back, and small black spots, and 

 another of the same variety with yellow belly, red spots, and an olive- 

 colored back. The like phenomena have been observed with trout of 

 the same variety in the lakes of Germany and Ireland. Differences of 

 food and habits, says Davy, may occasion, in a long course of ages, dif- 

 ferences of shape and color, which may be transmitted to offspring. 

 Trout that frequent clear and cold waters, and feed much on larvae and 

 their cases, are not only red in flesh, but they become golden in hue, 

 and the red spots increase and outnumber the black ones ; but when 

 feeding upon little fish they become more silvery in color and the black 

 spots increase. We have some singular examples of the effects of dif- 

 ference of diet. The peculiarity' of feeding on shell-fish produced the 

 gillaroo-trout, a remarkable variety foiind only in the Irish lakes. The 

 charr also is liable to great variations from the effects of its food, 

 and its history has, in consequence, been much confused by the natural- 

 ists. We observe similar effects with the Coregoni^ or white-fishes ; for 

 instance, the powan of the Scottish and the pollan of the Irish lakes. 

 Agassiz noticed that pet parrots, when fed upon certain fish of the 

 Amazon, changed colors, and their greeu plumage became spotted with 

 yellow. 



Age also often causes a great difference in the appearance of fish, 

 and the markings of the young change singularly with their growth. 

 The Cornish sucker has two large ocellated spots behind the eye, which 

 are not visible in the young fish. 



It is true that there is a marked difference in size between the lake- 

 salmon and the migratory salmon. There is also the fact that the one 

 seeks the sea, while the other does not. But these seeming distinctions 

 may be readily explained by the effects of food and locality. Sir Hum- 

 phrey Davy, who was an angler for fifty years, believed that differences 

 depending upon food and size will account for the peculiarities of par- 

 ticular fish, without supposing them distinct species. He sometimes 

 caught salmon quite unlike in form, markings, and color, and satisfied 

 himself that these differences were due to disease or to accidental cir- 

 cumstances. Young, in his admirable work on the history of the salmon, 

 gives a remarkable instance of singular differences occurring in a very 

 limited locality: " We know of five rivers which run into the same es- 

 tuary, and all and each of these rivers have their own peculiar salmon ; 

 and the fish differ so much, the one from the other, that they are quite 



