Figure l.--Rainbow trout used in the Leetown sonic experiments. 



sides are almost pure marl mud, a carbonate, 

 which absorbed sound very well. The structure 

 was placed in the center of the pond to avoid 

 standing or echo-waves of sound from inter- 

 fering with the beamed signal. 



In developing the naethod of investigation 

 and in designing the trough with its gates 

 and sections to measure the reaction of fish 

 to sound, three basic assumptions were made: 

 (1) if the trout were unaffected by or indif- 

 ferent to sound waves, they would move 

 within the trough amd between sections in a 

 pattern similar to that of the control; (2) if 

 they were attracted by some frequency of 

 sound they would tend to proceed to the end 

 of the trough nearest the sound source, or 

 (3) if the fish were frightened by the sound 

 they would travel away from the sound source. 

 Obviously, it was assumed that other stimuli 

 had no effect upon the movement of the trout. 

 Insofar as possible precautions against such 

 extraneous stimulation were taken. 



"WATER HAMMER" - ELECTROMAGNETIC 

 TRANSDUCER 



For the first tests with low audible fre- 

 quencies, the 600-pound audio speaker (fig. 6) 

 was suspended in the water so that the round 

 aluminum piston (lower center) was approxi- 

 mately 1 1/2 feet below the water surface, and 

 2 1/2 feet above the bottom. The heavy frame- 

 work to support it was erected at the extreme 

 end of the trough outside section No. 1. The 

 greatest intensity of sound, therefore, was in 

 section No. 1. The least intensity was found 

 in section No. 10, as determined by hydro- 

 phones. The speaker was never moved from 



1^^ 



C.U;. 





( 



Figure 2.--Dry pond, trap structure completed, gates rigged and in place. 



