ORIENTATION OF MIGRATING AXADROMOUS FISHES 



:is3 



Fi<iVRE a. — Upstream eml of exiieriiiifntal triiu;;li iluriui; 

 teiupei'ature tests. All imniei'slou water heaters are 

 in place for maximum temperature difference. 

 (Shade on left was raised to allow light for iJhoto- 



graphic purposes. During the experiments no shadows 



were present.) 



of the channel or channels in which the water was 

 to be modified. 



Tlie device used to accomplish this (fig. 7) con- 

 sisted of two batteries of porous-stone aerators of 

 the type commonly used in small aquariums. Each 

 battery of aerators produced a band of very fine 

 bubbles. The incorporation of two separate bat- 

 teries in tlie same device made it possible to modify 

 independently the Avater of both channels at tlie 

 same time. 



Nongaseous Chemicals 



The nongaseous chemicals used to modify water 

 in experiments were first dissolved in a carboy 

 of water from the stream. They were then intro- 

 (hiced at a controlled rate into tlic upstream end 



I'KjfiiK 7. — r>evice for iiinclif.viii^ };ase(jiis coiilcnt of watei'. 

 The device i-ontaiiied two separate batteries of aerators 

 so that the two clKMinels could he moditied independently 

 at the same time. 



of one of till' (liaiinels through a colorless plastic 

 lube jxisitioned horizontally an inch above the 

 Moor of the trough at riglit angles to the direc- 

 tion of stream flow. Small holes were bored in 

 tlie plastic tube at shoi-t intervals to allow an even 

 distribution of the carboy liquiil throughout the 

 channel. 



MEASUREMENTS 

 Water Samples 



AVater samples were collected in wide-mouthed 

 100-milliliter bottles at tiie downstream end of 

 each channel. Samjjle bottles were stoppered 

 while still under water to avoid any gaseous ex- 

 change with liu' air. Tlie samples were collected 

 simultaneously in both cliamiels and were imme- 

 diately brought into the lield laboratory where the 

 clieinical ilciciiuinai ions were beofiin at once. 



