Pulse frequency and pulse duration were both measured on a special oscilloscope 

 designed and constructed for laboratory experiments in fish guiding (Volz, unpublished 

 manuscript). 



Water resistance was maintained between 7, 250 ohms/cm. and 10, 000 ohms/ 

 cm. ; it was determined by an industrial Instruments Conductivity Bridge Model RC-IB. 

 Water temperature varied between 8.0° C. and 16.0° C. and was determined v/ith a 

 standard mercury thermometer. Water resistance and the temperature were recorded 

 before each series of tests. 



Silver salmon ( Oncorhynchuis kisutch ) ranging in size from 5.5 cm. to 12 cm. 

 total length, measured from the tip of the snout to the end of the tail, tlie only species 

 used in these tests, were obtained weekly at the Washington State Fish Hatchery at 

 Issaquah, Washington, and transported to the laboratory in Seattle where they were 

 placed in round metal holding tanks. Immediately prior to use they were removed in 

 small lots of from 150 to 200 fish and placed in a smaller trough near the experimental 

 area from which they were taken in groups of 60 fish for each test . 



Four groups of fish were used each time for each test condition. T'.vo of the 

 groups of fingerlings (2d and 3d) were released while the electrodes were supplied 

 with electrical energy and two groups (1st and 4th) v/ere released when tJhe electrical 

 energy' was not supplied; the 1st and 4th groups of fish were designated as control 

 groups to ensure that an increase in numbers found in the narrow channel was the 

 result of the electrical field and not due to the changes in hydraulic patterns created 

 by the electrodes or leading as the result of a visible barrier. 



The fingerlings that were exposed to the electrical current and recovered from 

 the traps were returned to a second round metal holding tank until all fish on hand had 

 been exposed once; this procedure was followed to maintain the same condition for all 

 fish in any series of tests . Since preliminary tests had indicated that conditioning 

 might influeirce the behavior of fish exposed three or more times to electrical condi- 

 tions, the fingerlings were exposed only twice; the same handling procedure was 

 followed in every experiment. The control group of fingerlings, that had not been 

 exposed to electrical energy, were returned to the original. tank from which they were 

 taken until they had been exposed to electrical conditions, after which they were 

 handled as described above. 



Prior to release of the fish, the light intensity was subdued to less than 1 foot- 

 candle and the electrodes were energized. The salmon fingerlings v/ere tlien released 

 in groups of 60 individuals upstream from the experimental area (fig. 1) equally 

 divided into the two middle channels. (On the one exception to this procedure, 200 

 fish were released to investigate the effect with large numbers) . Once the fish were 

 released the light intensity was reduced to a minimum and the tank remained in almost 

 total darkness for 5 minutes. At the end of that time, the light intensity was very 

 slowly increased to a maximum , 



