390 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 13. — Experiments testing orientative influence of 

 oxiigen and nitrogen 



1 stream temperature, 15.4° to 19.1° C. O2 content of immoditied stream 

 water, 10.5 to 10.7 p. p. m. Oj difTcrence between chamiels, 1.1 p. p. m. 



experiments unfortunately provide no informa- 

 tion on the possible effect of differences in O2 at 

 lower values where differences may be very 

 important. 



OTHER FACTORS INFLUENCING ORIENTATION 



Although the major experimental efforts of this 

 investigation were concerned with the orientative 

 influence of temperature and dissolved gases, ex- 

 ploratory experiments also examined the influence 

 of other factors. 



The influence of water velocity upon the orien- 

 tation of the migrating fish was explored by sub- 

 jecting tlie fish to a clioice between waters of dif- 

 ferent velocities. The difference in velocity be- 

 tween the two channels was created by placing a 

 glass plate across the upstream entrance to one of 

 the channels, restricting the amount of water en- 

 tering that channel and so reducing the velocity 

 of the water in the downstream end of the channel. 

 The response of the fish (table 14) indicated that 

 water velocity could be a factor in fish orientation. 



The influence of water turbulence upon the ori- 

 entation of the fish was explored in a similar man- 

 ner. The turbulence in one of the. channels was 

 reduced by placing glass plates, several feet in 

 length, in the center of the channel parallel to 

 the channel walls. This produced a flow which 

 was smooth and laminar in appearance. In the 

 other channel, small glass plates were set at an 

 angle to create eddies which produced a visible tur- 

 bulence. Most of the fish selected the channel 



Table 14. — Orientative influence of velocity 



with less turbulence (table 15). CO2 was then 

 added to the channel with less turbulence in order 

 to discover the relative influence of turbulence and 

 CO2. The data indicate that CO, had the greater 

 orientati\e influence. 



Table 15. — Orientative influence of turtjulence and CO1 



I CO2 added. 4 p. p. m. 



All exjiloratory experiment was made which in- 

 dicated that visual factors may influence fish 

 orientation. The downstream end of one chan- 

 nel was partially blocked (see fig. 9). The fish 

 normally swam within a few inches of the bottom 

 of the trough so that the "obstacle" did not inter- 

 fere in any physical way with their progress. 

 However, most of the fish entered the channel 

 which was completely unobstructed. To examine 

 the relative influence of this visual factor and 

 temperature, the water of the partially blocked 

 channel was heated 2° C. The data (table 16) 

 show that under these conditions temperature was 

 the dominant orienting factor. 



These tests were crude experiments of an ex- 

 ploratory nature. There undoubtedly were some 

 velocity differences involved in the turbulence 

 tests. The partial block at the downstream end 

 of one of the channels in the tests involving the 

 visual factor probably created slight differences 



WOODEN BLOCK 

 (3\ 



OPEN 



Figure 9. — "VisuiU" l;ii-ti>r (cxplorulitry U'Sts). 



