170 BULLETIN OF THE BUREAU OF FISHERIES. 



.speciineiis consisted chiefly of .such forius a.s fell into the water accidentally. In 

 view of this fact, and also in view of the dietetic importance of these insects, a study 

 of the food of these trout during- the long winter period when the laives are covered 

 witli ice would lie ver}" interesting, as well as necessar}- to a good understanding 

 of their food habits. The winter period is, undoulitedly, the most critical for them 

 so far as food is concerned. That food was sufficiently abundant during tlie summer 

 was shown by the good physichal condition of the trout, and by the quantity of fat 

 that was found iii most of them. 



The rainbow and the large brook trout had the greatest variet}^ of insect diet. 

 Each had partaken of 10 of the 13 items listed, while the greenback trout had par- 

 taken of s and the landlocked salmon 7. Not more than three or four forms of 

 insects, however, played an important role in the food supply of any species of trout. 

 Named in the order of their importance, Coleoptera, Trichoptera, Diptera, and 

 ShiiuIii(iJi constituted by far the greater bulk of the recognizable insect food of the 

 landlocked salmon, the four together making up an average of 36.1 per cent of the 

 stomach contents in all the specimens. Coleoptera, Diptera, Lepidoptera, and Orth- 

 optera were the important insect elements in the food of the greenback trout, and 

 together constituted -±6.3 per cent of the stomach contents. The rainbow trout had 

 eaten most freely of Coleoptera, Lepidoptera, and Diptera. but these three made up 

 only 14.1 per cent of the stomach contents. 



A comparison of the results obtained for the small and t\w large brook trout 

 shows that the}' differed greatly in their insect food. The small ones fed freelj' on 

 May-fl.y nymphs and on the larvw and pupie of CIiii'inKunus unA SuiadiiDn. Adult 

 Diptera ranked second in importance, howevei', being exceeded only by the May -fly 

 nymphs. These four groups together made up a little over 48 per cent of the food 

 of these specimens. Hymenoptera, Coleoptera, Orthoptera, and Chironoiin(» formed 

 the most important part of the insect food of the lai'ge ])rook trout, and together 

 constituted 23.1 per cent of the stomach contents. 



Diptei'a, C'/n'ronomus, and Lepidoptera were the most important elements of the 

 food of the trout ivy. The Ephemerida were represented almost entirel}' by n3'mphs, 

 and the Triehoptei-a by larva\ The Lepidoptera consisted almost entirely' of moths, 

 and by far the greater part of the Hymenoptera were ants. The high percentages 

 of Coleoptera were undoubtedly due, in a great measui'e, to the resistance of the 

 chitinous elytra and other coverings to the process of digestion. 



Examination of some trout from streams in the region of JNIount AVhitney, Cali- 

 fornia, revealed the fact that in those waters also only a few forms of insects were 

 an important part of the trout food. In 13 specimens obtained from the South Fork 

 of the Kaweah liiver, the three most important elements of the food, which consisted 

 entirely of insects, were chironomid larvre and pupa3 15 per cent, Coleoptera 15, and 

 trichopter larvaj 11.3. In fi trout from Soda Creek, the most important elements 

 were as follows: Trichopter larva% 30.8 per cent; Plecoptera, adults and nymphs, 

 9.3; and Orthoptera, Coleoptera, and Hymenoptera each 4.1 per cent. In 41 speci- 

 mens from Little Kern liiver, Coleoptera and Hymenoptera were each 15 per cent 

 of the food. The following percentages of insect food were obtained for 18 speci- 

 mens of the golden trout {Salmo roosevelti) from Volcano Creek: Plecoptera (adults 

 and nymplis), 13.3; Trichoptera (adults and larvw), 7.2; ephemerid nymphs, 7. 



