SALMONOID FISHES. 15 



the size of the scales, and the number of rows in which they are 

 arranged, the positions of the fins and the number of fin-rays in 

 each, the characters of the teeth and the proportions of the bones 

 of the upper jaw and of the gill cover, these characters being 

 reasonably stable, whereas the colouring is largely dependent on the 

 conditions in which the fishes live. As a rule the fresh-water 

 forms are brown or reddish, and the marine forms bright and 

 silvery, and in the case of migratory forms like the Salmon and 

 Sea Trout the change from the one colour to the other is to be 

 observed in the same individual at different periods of its life. In 

 the non-migratory forms the colours are fairly constant while the 

 fish remains in the same waters, but by transferring to new localities 

 brown forms may become silvery and silvery forms brown. 



The relation that obtains between the environmental conditions 

 and the colouring of the fish is expressed by Dr. Gunther * in the 

 following terms : — " Trout with intense ocellated spots are generally 

 found in clear rapid rivers and in small open alpine pools ; in the 

 large lakes with pebbly bottom the fish are bright and silvery, and 

 the ocellated spots are mixed with or replaced by X -shaped black 

 spots ; in pools or parts of lakes with muddy or peaty bottom the 

 trout are of a darker colour generally ; and when enclosed in caves 

 or holes they may assume an almost uniform blackish coloration." 

 The remarkable differences in the colouring of Trout living in 

 neighbouring, but non-communicating, waters is nowhere better 

 exemplified than in Sutherland. Loch Scourie, Loch Crocach, 

 Loch Borlane and Loch Manse all have their own particular type 

 of Trout (see 995, 997, 996, 994). In deep lakes where food is 

 fairly abundant the Trout grow to a large size, and such fish are 

 called Great Lake Trout, fishes long known as Salmo ferox. The 

 specimen of Great Lake Trout, 999, exhibited in the Cabinet-case, 

 is from Windermere. 



In Loch Leven the Trout, formerly described as Salmo levenensis, 

 are slender and more silvery than most non-migratory Trout, with 

 less yellow along the sides of the abdomen and with spots that are 

 dark and without any scarlet. Examples of a male and a female 

 are shown (991, 992). The Galway Trout, of which a specimen 



* "An Introduction to the Study of Fishes," 1880, p. 632. 



