256 



BULLETIN OF THE BUREAU OF FISHERIES. 



list of terrestrial beetles recorded by Forbes, many of whose fish were taken in rivers 

 and streams, it would seem reasonable to infer that in the trout recorded by Juday 

 from rivers and creeks much of the beetle food was terrestrial. This, however, 

 does not in any way affect the conclusions that follow, since the trout that captured 

 and swallowed a terrestrial species would do the same to an aquatic species, if the 

 opportunity offered. Beetle systemy will not, to any appreciable extent, affect a 

 trout's appetite. 



Of the 421 trout examined by Doctor Juday 40 per cent had eaten beetles, 

 and in their stomachs the beetles formed on an average one-quarter of the total 

 food. Such a percentage is large enough to constitute an important factor in the 

 food supply of these fish. It will be noted that a larger number of individuals taken 

 in running water had eaten beetle food, the percentage reaching as high as 92.68 

 in the Little Kern River. On the contrary the relative amount of beetles in the total 

 food was greatest in the trout from the quiet waters of the Twin Lakes, reaching an 

 average of 73 per cent in the four landlocked salmon. Again the smaller fry, from 

 2.5 to 5 cm. in length, consumed practically no beetles, whereas the medium-sized 

 fish, from 10 to 40 cm. in length, consumed the greatest amount. 



The largest landlocked salmon was 70 cm. in length and the smallest one 20 

 cm., and although no data were given as to the length of the four that had eaten 

 beetles, we may infer from the other statistics in the table that they were among the 

 smaller rather than the larger ones. Beetles, therefore, do not become a factor in 

 the food of trout until the fish have reached a length of 7.5 cm. (3 inches). The 

 fingerlings then begin to eat them freely, and diu-ing the period of growth from 10 

 to 30 cm. beetles form an important part of the total food. 



For trout above 30 cm. in length other fish become a more and more 

 important item of food until they practically supplant everything else. Of the 64 

 greenback trout {Salmo stomias) only four had partaken of fish; none of the small 

 brook trout had touched them, and only two of the 126 large brook trout and none 

 of the trout from the creeks and rivers had eaten fish. On the other hand, seven 

 of the landlocked salmon, presumably the larger ones, had eaten nothing but fish, 

 that item constituting 100 per cent of their food. 



The percentages given for each species in this table were obtained by dividing 

 the sum of the per cents of the different food items by the number of stomachs 

 containing food. Of the 12 food items of the landlocked salmon, fish was the only 

 one that surpassed beetles. In the greenback trout, also with 12 food items, Crus- 

 tacea and beetles were the two largest, the former 0.22 per cent larger than the latter. 

 In the rainbow trout, with 17 food items, beetles were the third in abundance, being 

 surpassed by fish and vegetable debris. In the large brook trout, with 16 food 

 items, beetles were surpassed only by vegetable debris and Hymenopetra. For 

 the small brook trout beetles formed the smallest of the 10 food items. 



