A STUDY OF TWIN LAKES, COLORADO. 



167 



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

 food, 42 had partaken of fish; and while all the remains that could Ije identified were 

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

 pi'eys upon young trout too, since small tish constitute such an important element of 

 its food. 



Of the 16 specimens that contained Crustacea, one had eaten Gaininarus, one 

 copepods, another Diaptomi and Daplutla^ while the other 13 had partaken of 

 Daphnia only. One stomach contained 1,350 Daphnia. 



The vegetable debris consisted of spi'uce leaves, pieces of wood, I'otainogeton 

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

 feather. Much of the vegetable debris was probabh' taken b}^ accident, but some had 

 apparently been eaten on purpose. Mucliof the sand was probably derived from tlie 

 cases of trichopter larvte. 



Machinaw trout {Crldivomrr namayeusJi). — Two Mackinaw trout were obtained. 

 One was 30 inches (Tfi centimeters) long, and its stomach contained a trout 7 inches 

 (17.5 centimeters) long and a few insect fragments; the other specimen was 33 inches 

 (84 centimeters) long, but its stomach was empt}\ Mr. Willis examined the stomachs 

 of several large specimens caught in 1903 and found that they contained almost 

 nothing but J'oung suckers. 



Milner (1874) states that in the Great Lakes this trout feeds principally on the 

 cisco {Argyrosoimis hoyi). "It is not an unusual thing for a trout to swallow a fish 

 too large for its stomach and the tail pi'otrudes from his mouth until the forward 

 part is digested." He 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 bones having been found in stomachs. Groode (18S4) says that Mackinaw 

 trout are as omnivorous as cod. 



SmaUhrooTi trout {Salvel imis font inuJ is). — Twenty-nine specimens of small brook 

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

 1902. Thej' were caught in Lake Creek, above and between the lakes, and in Upper 

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

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



Contents of utoiiiai-hx of 29 small brook trout. 



Foud elements. 



Number 

 of speci- 



mena 

 in which 



found. 



Ephemerida ; 11 



Plecoptera I i 



Orthoptera 2 



Lepidoptera imothsj ' 1 



Diptera I 10 



Average 

 percent 



of 

 element. 



59.0 

 25,0 

 22.5 

 20.0 

 33.7 



Food elements. 



Chironomu.s (larva' and pnpie) 



Simulium (larvce) 



Coleoptera 



Insect fragments 



Vegetable di^bris 



Number 

 of speci- 

 mens 

 in which 

 found. 



Average 

 per cent 



of 

 element. 



20.3 

 46.2 

 5.0 

 63.6 

 10.0 



Lan/e hrook trotd {S(tl reli tins fontinalis). — The specimens of larger brook trout 

 numbered 127 and varied in lengtli from 4 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; 79 were estimated to be a third full or 

 more and the remainder a quarter full or less. 



