36 



The minimal concentrations affecting respiration of natural 



and hatchery -reared advanced sockeye alevins were 0.3 ppm and 0,1 



ppm tetrachlorocatechol, respectively. These concentrations were 



approximately 25 per cent and 10 per cent of the 96-hr TL 's 



m 

 determined for these alevins. Reasons for the different degrees 



of response were not apparent but may have been related to 



experimental variation or some characteristic of the alevins. The 



sockeye fry responded slightly to O.IC ppm tetrachlorocatechol 



which was 12.5 per cent of the 96-hr TL for these fish. 



ra 



Respiration rates of pinlc salmon alevins at 0.10 and 0.125 ppm 



tetrachlorocatechol fell below those of the controls and it was 



therefore difficult to estimate a minimal concentration. If 



increase in respiration rate were the only criterion, it coiold be 



estimated that the miniinal concentration would be between 0.125 



and 0.15 ppm, or about 0.135 ppm. On the other hand, if the 



observed decrease in respiration rate was caused by 



tetrachlorocatechol at 0.10 ppm, then this would be the minimal 



concentration at which a respiration response occurred. The 



former value is about 4-6 per cent of the 96-hr TL and the latter 



m 

 about 34- per cent. The minimal concentration of tetrachlorocatechol 



for pink salmon fry was between 0.10 and 0.150 ppm, or about 



0.125 ppm, approximately 48 per cent of the 96-hr TL . 



m 



The preceding comparisons indicate that tetrachlorocatechol 

 interfered with normal metabolism of young sockeye, apparently by 

 uncoupling oxidative phosphorylation, at minimal concentrations 

 ranging from 10 to 25 per cent cf the 96-hr TL and averaging 

 about 15 per cent. Interferenci,- with metabolism of young pink 

 salmon definitely occurred at rdnimal concentrations of 4.6 and 48 

 per cent of the 96-hr TL. raid possibly at 34 per cent. 



It is interesting to compare the reported range of 

 concentrations over which another toxicant, Dieldrin, affected 

 respiration. Dieldrin, aji insecticide which affects the central 

 nervous system, caused about an 18 per cent increase in oxygen 



