A STUDY OF TWIN LAKES, COLORADO. 



167 



upon its congeners." In the present case, out of a total of lot; specimens containing 

 fond. 4-_' had partaken of fish; and while all the remains that could lie identified were 

 found to lie suckers, it does not seem at all unlikely that the rainbow occasionally 

 prevs upon young trout too, since small fish constitute such an important element of 

 it- food. 



Of the l»i specimens that contained Crustacea, one had eaten Gammarus, one 

 copepods, another Diaptomi and Daphnia, while the other L3 had partaken of 

 Daphnia only. One stomach contained 1,350 Daphnia. 



Th< vegetable debris consisted of spruce leaves, pieces of wood. Potamogeton 

 leaves, and. algse. One stomach, contained a piece of cotton twine and another a 

 feather. Much of the vegetable debris was probably taken byaccident, hut some had 

 apparently been eaten on purpose. Much of the sand was probably derived from the 

 cases <>f trichopter Ian ■■<-. 



Mackinaw trouti Cristivomer namaycush). — Two Mackinaw trout were obtained. 

 One was 30 inches (76 centimeters) lone-, and its stomach contained a trout 7 inches 

 1 17. "i centimeters) lone- and a few insect fragments; the other specimen was :;:; inches 

 (84 centimeters) lone-, hut its stomach was empty. Mr. Willis examined the stomachs 

 of several large specimens caught in L903 and found that they contained almost 

 nothing but young suckers. 



Milner ( ls7t) states that in the Great Lakes this trout feeds principally on the 

 cisco (Argyro80?nus hayi). ""It is not an unusual thine- for a trout to swallow a fish 

 too large for its stomach ami the tail protrude- from his mouth until the forward 

 part is digested." rle also says that it eats refuse from the tables of passing steam- 

 ers; such articles as peeled potatoes, pieces of liver, green corncobs, and fragments 



of ham hones having been found in stomachs. <> le (1884) says that Mackinaw 



trout are a- omnivorous as cod. 



SmallbrooA tr<>>tf ( Salvelinvs fontinalis). Twenty-nine specimens of small brook 

 trout from 1 to 2 inches (2.5 to 5 centimeters) long were obtained in duly and August, 

 1902. They were caught in Lake ( 'reek, above and between the lakes, and in Upper 

 Lake. The st achs of all of them contained food, and most of them were esti- 

 mated to be from a third to two-thirds full. 



Contents of stomach - all brook trout. 



Food elements. 



Number 

 oi speci 



mens 

 in which 



found. 



Ephemerida 



Plecoptera 



Orthopteia 



Lepidoptera I moths 

 Diptera 



of 

 element. 



69.0 

 25.0 

 22. :> 

 20 

 33.7 



 Lements. 



ChironomTJS (larvae and pupae 



Simullum I larvae) 



Coleoptera 



I n -'it fragments 



Vegetable debris 



Keel' * 



'„!,;. Percent 



in which 



of 





.•lenient. 



20.3 

 46.2 

 5.0 

 63.6 

 in 



Large brook trout (SalveMmcs fontinalis). — The specimens' of larger brook trout 

 numbered 1l'7 and varied in length from i to 13 inches (10 to 33 centimeters). Of 

 this number, 117 were caught in Lake Creek above Upper Lake, 7 in Upper and 3 in 

 Lower Lake. Only one stomach was empty; 70 were estimated to be a third full or 

 more and the remainder a quarter full or less. 



