Before starting the sonic tests^ 100 trout were placed in each 

 of the ten sections of the trough. Fifty trout of the same stock were 

 placed in one live car near shore and several large brood rainbow up 

 to 2li inches in length were placed in another where their reactions to 

 each frequency could be observed at close hand. Before the planned 

 tests and controls were started, it was decided to try the full range 

 of the low frequency equipment briefly to s ee if one oarticular fre- 

 quency response could be singled out. Observations were made directly, 

 irith Dr. Rounsefell standing motionless at section no, 1. Mr. Neal 

 watched the large brood rainbow in the live car near shore from a dis- 

 tance. The following notes were made: 



(1) 67 cycles per seconds Rounsefell noted fish appeared 

 uneasy at low range especially when sound vjas first turned 

 on. Fish started and faced away from the audio speaker 

 but did not swim off when sound continued. 



(2) Siren effect 6? cps, to 700 cps. Rounsefell observed 

 whole school of fish face away from speaker, but returned 

 to normal in seconds. 



(3) Intermittent operation all frequencies from 67 to 3,000 

 cps. No effect, 



(h) Neal reported no response from brood rainbow near shore. 



Following the brief tests described above, those frequencies 

 which elicited even the slightest resoonse were tested systematically 

 by octaves (i. e. 70 cps, to lIiO cps. etc.). It m^s evidence from 

 their reaction, that the fish were able to detect the source of sound 

 at the moment of starting. It is doubtful, but entirely possible that 

 a visual stimulus was received in addition to the audio stimulus. The 

 aluminum piston of the audio speaker had a travel of less than l/" inch. 

 It was located some distance from the fish and outside the wire trough. 



Some sound emitted by the underwater speaker escaped into the air 

 and could be heard plainly as a steady buzz at a distance of $0 yards. 

 At a distance of 1 yard the escaping sound was likened to that of an 

 irritating door buzzer at arm's length. The same sound intensity under 

 water is multiplied nearly 1^0 times - a fact familiar to the small boy 

 who strikes rocks together below the surface with his head submerged. 

 The fish, therefore, were being subjected to an intensity of sound much 

 greater than is perceived by the human ear above the water surface. 



Figures 8-l5 with histograms shoxiri.ng the results of each test are 

 presented to give the reader an opportunity to compare the results of the 

 sound tests and the controls. For the first several tests, fish were 

 counted out 100 to a section and renlaced 100 to a section after pach 

 test. In each case, the darkened portion of the histogram represents the 

 numbers of fish found after each control or test run. 



