The picture was taken in total darioiess 

 with an infrared 22R flash, with an exposure 

 of 1/30 second at a stop opening of f/3.5. 

 Some indication of as yet unexplored pos- 

 sibilities is afforded by the penetration 

 evidenced in the photograph in figure 9, taken 

 at night off the laboratory dock. The mark- 

 ers are 1 foot apart. The exposure was 1/30 

 second at f/3 . 5 with the 22R infrared flash . 



Former military image -converter 

 tubes and optical systems are also avail- 

 able, but must be assembled for use. 

 Readily obtainable parts for the power 

 units must likewise be assembled. In the 

 absence of a viewer, indirect photographic 

 observations m.ay be made in the dark 

 through the use of infrared film and suit- 

 able radiation. 



Animal Reaction 



Uses 



An examination of the literature has 

 failed to yield evidence that fish or other 

 animals possess the capacity to detect infra- 

 red radiations by visual means. Direct 

 evidence as to whether other animals do de- 

 tect them is scanty, and lacking for fishes. 

 The gross experiments conducted in this 

 laboratory with silver salmon (0_. kisutch) 

 failed to yield evidence that the fish could 

 detect, or were affected by, infrared radia- 

 tion. Individual species whose behavior is 

 to be studied by this means should first be 

 investigated for reaction to infrared radia- 

 tion, but use of the tool is not precluded by 

 a priori evidence . 



Equipment 



The ordinary high -temperature tungsten 

 lamp delivers most of its energy in near- 

 infrared radiation, in the infrared region of 

 greatest penetration in water. Such lamps, 

 screened by proper filters, may be used to 

 provide any desired degree of intensity. 

 The therapeutic infrared lamp is not suitable 

 for observation of fish behavior because of 

 the water -absorption characteristics of the 

 wavelengths emitted. 



Complete absorption of the visible spec- 

 trum by the filter is vital in fish -behavior 

 studies, and for this reason filters suitable 

 for darkness photography may fail when used 

 over the light source . Suitable filters found 

 military application and have been made 

 available commercially . 



There are many potential laboratory 

 and aquarium applications of infrared 

 radiation; behavior studies and direct ob- 

 servation of the habits of aquarium speci- 

 mens may be readily extended by the 

 observer being able to see in the dark . 

 Questions concerning the importance of 

 vision in orientation, for example, may be 

 examined by observation rather than ex- 

 perimentation. Some diurnal -activity 

 patterns can be established or confirmed. 



The present laboratory use of infrared 

 radiation in connection with electrical - 

 guiding studies has an immediate extension 

 into field use as the guiding apparatus is 

 tested on a larger scale. Ultimately it may 

 find employment at full-scale installations, 

 and in each instance perhaps contribute to 

 needed data . 



The tendency of fingerling Pacific sal- 

 mon to migrate seaward during the hours 

 of darkness provides a wealth of opportunity 

 for behavior studies under natural condi- 

 tions . Among practical applications may be 

 mentioned the possibly more precise and 

 rapid locating of sampling devices . 



Data are needed on the effectiveness of 

 the location, size, and design of fishway 

 orifices and the entrances to bypass channels 

 Infrared radiation, with underwater tele- 

 vision, could render service in observing 

 undisturbed behavior at present installations, 

 and supply information valuable in the de- 

 sign of future applications . 



14 



