20 



relative respiration rates shown in TABLE 5 and were plotted in 

 FIGURE 2. Over the range of concentrations tested it appeared 

 that relative respiration was proportional to tetrachlorocatechol 

 concentration. However, average respiration rates of naturally 

 spawned alevins decreased faster than those of hatchery alevins as 

 tetrachlorocatechol concentrations decreased. The difference in 

 slope of the data for natural and hatchery alevins may have been 

 related to incubation conditions, alevin size, or temperature. 

 Note that bodies of hatchery alevins used in Trial h were a little 

 larger than those in the other trials. Furthermore, alevins from 

 natural spawn used in Trial B were slightly smaller than those in 

 Trials C and D but there was a large difference in the amount of 

 yolk remaining. Since these alevins were obtained from the same 

 spawning area, a difference in egg size or natural incubation 

 conditions may have influenced development. Temperature has a 

 marked effect upon respiration rate, but in order for it to affect 

 relative respiration rate it would have required that temperature 

 not have a parallel effect on respiration of test and control fish. 

 Further research would be required to define the importance of 

 these various factors. 



The data in TABLE 5 and FIGUriE 2 do not permit precise estimates 

 of the lowest concentrations of tetrachlorocatechol at which 

 respiration rate was increased and further experimental work would 

 be reqiiired in order to make these estimates. However, the 

 accumulated data suggest that respiration of the hatchery and natiiral 

 alevins was accelerated at concentrations greater than 0,1 and 0.3 ppm 

 tetrachlorocatechol, respectively^ 



In order to confirm that dichlorocatechol would act on salmon in 

 the same manner as tetrachJ.orocatechol, the relative respiration rate 

 of hatchery- incubated Cultus Lake sockeye alevins (similar to Trial a) 

 was determned at a single concentration using duplicate samples of 



