FISHES OF COLORADO 77 



are almost no data from either Colorado fishermen or Colorado collections. The 

 belief is current that the various native trout cross with the introduced Rainbow 

 Trout and several reports of such hybrids have reached the University. The 

 writer was also assured that SteeUieads and Eastern Brook Trout crossed when 

 kept in a lake near Durango. As opposed to such reports Jordan states that he 

 "has examined many thousands of American Sahnonidae, both of Oncorhynchiis 

 and Salmo," and "while many variations have come to his attention, and he has 

 been compelled more than once to modify his views as to specific distinctions, he 

 has never yet seen an individual which he had the slightest reason to regard as 

 a 'hybrid.'" On the next page he quotes Giinther as writing that "hybrids 

 between the salmon and other species are very scarce everywhere." That hybrids 

 between some species of the genus Salmo are possible when the eggs are artificially 

 fertilized is established by experiment, and Mr. S. E. Land of the Colorado State 

 Fish Commission told the writer that such an artificial cross had been successfully 

 made between the "Native" and the Rainbow at the Denver Hatchery. No 

 specimens of authentic hybrids either from nature or from artificial fertilization 

 have been examined in the present study. 



Trout are primarily fishes of the mountain streams and lakes since they are 

 physiologically adjusted to live in cold clear water with a high oxygen content. 

 All are carnivorous, feeding as adults for the most part on other fishes and to some 

 extent on insects and other stream animals. Aside from man the chief enemies 

 of the trout are the Sculpin,^ Coitus punctulatus, the Dulcis Minnow, Rhinichthys 

 dulcis, Yarrow's Dace, Agosia yarrowi, and the suckers, all of which destroy trout 

 eggs. Of these fishes the Sculpin is the most harmful smce it is rarely eaten by 

 the trout yet feeds upon both the young trout and trout eggs. Between the 

 suckers, Dulcis Minnow and Yarrow's Dace, and the trout there exists a com- 

 pensating relation which makes each group of value to the other. The former 

 eat trout eggs but the young suckers and both young and adults of the Dulcis 

 Minnow and Yarrow's Dace collectively form one of the most important items 

 in the food of the adult trout. It has been shown that trout do not thrive in 

 streams in which young or small fish are not available for food. In lakes where 

 the supply of insects is greater the presence of small fishes is not so essential but 

 they nevertheless form a considerable portion of the food of the adult trout when- 

 ever present. Other factors limiting the number of trout in Colorado streams are 

 overfishing, the introduction of mine and mill waste into the trout streams and 

 the deflection of water for power or irrigation purposes. 



The species of trout found in Colorado may be separated by the following 

 key. Since the various colors and markings of the trout vary with the individual 

 and to some extent with the immediate environment as well as the season, it is 

 diflacult to give characters which wiU cover all specimens. Typical specimens 



' See pp. 64, 68, and 114. 



