Living Fishes 1 19 



Further north, Salmo lewisi has been seen in the very act of passing 

 from the Pacific to the Atlantic drainage, as is recorded by Jordan 

 and Evermann. 



The study of the food of fishes is equally of scientific in- 

 terest and practical importance. Many feed on insects, molluscs, 

 or on other fishes; but certain species are herbivorous. The 

 number of insects consumed by a single fish is astonishing. On 

 one occasion, in Devonshire, England, Dr. C. L. Perkins studied 

 and catalogued the insects found within a single individual trout.* 

 The list includes a dragon-fly nymph, two kinds of Diptera, six 

 species of ants, a yellow-jacket wasp, four kinds of Hemiptera, a 

 caddis fly and two kinds of caddis fly larva-cases, two sorts of 

 moths, and no less than 45 different species of beetles! It will 

 readily appear from this how dependent our game fishes are on 

 the supply of insects, and thus indirectly on the stream-side and 

 aquatic vegetation. It is true that many of the insects con- 

 sumed by this trout are themselves predatory, but ultimately 

 all predatory animals have to depend on plant-feeding ones. 



To one who would identify our fishes, most of the species 

 present little difficulty, especially if the known distribution is 

 taken into account. The members of the Salmonidae or salmon 

 and trout family are characterized by the soft fins, and small 

 adipose fin over the base of the tail. The native and introduced 

 species are described and tabulated in detail by Ellis in the work 

 already cited. The Whitefish (Coregonus williamsoni of Girard) 

 is found only in the northwestern part of the State. It is silvery 

 on the sides, bluish above, without spots. The salmon and trout 

 proper are divided into three genera, of which only one (Salmo) 

 is truly native in Colorado. The Mackinaw Trout (Cristivomcr), 

 a very large fish, has been introduced into Twin Lakes. The 

 fins are much mottled, and there are no bright red spots. The 

 Eastern Brook Trout (Salvelinus fontinalis) is now well established 

 and common. It is spotted with bright red (the spots never ringed 

 with white), and the lower fins have the anterior margins white. 

 Our most interesting native trout is Salmo clarki macdonaldi , 

 of Jordan and Evermann, found only in Twin Lakes, and now 

 possibly extinct as the result of introducing alien species. It is 

 known especially by the bright yellow pectoral, ventral and anal 



♦Journal Torquay Natural HUtory Society, 1921. 



