Table 1 . --Influence of radiation in displacement of fingerling silver 



salmon (O. kisutch) in still water 



Radiation in opposite 

 compartment from fish: 



Average of six trials, 50 fish per trial. 

 ** Hq: Movement is not influenced by radiation (is the same as in darkness), 

 # Highly significant. 



of a few seconds after the overhead light 

 was extinguished. The photograph shown 

 in figure 5 was taken in total darkness on 

 infrared film, with the infrared source 

 focused on the tank and an infrared flash 

 bulb used as an auxiliary "light" source. 

 The exposure was 1/30 second at f/3.5. 



Orientation in flowing water is also con- 

 sidered to be accomplished, at least in part, 

 by visual means. Accordingly a trough 12 

 feet long was marked off in 15 numbered 

 sections, with heavy black lines running 

 across the bottom and up the sides at 8 -inch 

 intervals . Two purposes were served by the 

 procedure: Reference points were provided 

 for the fish; and a means was established of 

 measuring whether orientation was main- 

 tained in darkness or under infrared illumina- 

 tion . The infrared beam was directed along 



the trough from above the overflow end. 

 It did not illuminate the trough evenly, 

 as seen through the telescope, but appeared 

 brightest in the region from section 10 

 through section 6. The apparatus is shown 

 in figure 6. 



The photograph of figure 6 was taken 

 under the conditions of the experiment, ex- 

 cept that additional infrared radiation was 

 supplied temporarily by a filtered 1, 000- 

 watt spotlight. The film used was the 

 infrared- sensitive Kodak IR 135, and the 

 exposure was 8 seconds at a stop opening 

 of f/3 .5 . The closeup shown in figure 7 

 is presented to illustrate the use of black- 

 and-white film with the infrared telescope. 

 The photograph was taken through the view 

 plate of the telescope on Ansco Superpan 

 Press film with an exposure of 1/2 second 



