10 



0.8 - 



06 - 



§ a« - 



Q- 



O _ 



0.2 - 



00 



100 



105 110 115 120 125 130 



GAS SATURATION IMEAN TOTAL DISSOLVED GASI 



135 



FIC. 4 Acute bioassays of dissolved gas tolerances of Iclalurus 

 melas (Black Bullhead) at 20 C. 



8 12 16 



TEMPERATURE (TEST AND ACCLIMATION, °CI 



FIC. 5 Effect of temperature on tolerance of Ictalurus melas 

 (Black Bullhead) to excess dissolved gas tension. Bars represent 

 fiducial limits about the Tl ,„ value. 



Fig. 5 is a plot of the 96-hr TL 50 values with their 

 fiducial limits at each of the test temperatures. The 

 tolerance at the lowest test temperature is statis- 

 tically significantly greater than that at the higher 

 temperatures. It is important to note that the dif- 

 ferences are small and not of ecological significance 

 as greater perturbations in gas tension take place 

 over short periods of time in nature. An active fish 

 moving vertically in the water column will also 

 experience greater changes in the compensatory 

 effect of hydrostatic pressure. 



Tests with rainbow trout are continuing, but we 

 are able to report that at 20°C the TL 50 is about 118% 

 total gas supersaturation, a value significantly lower 

 than that for black bullhead, both from a statistical 

 and an ecological basis. 



To summarize our findings, the effect of tem- 

 perature within the range tested has little effect on 

 tolerance of black bullhead acclimated to the test 

 temperature. Future tests are planned at tempera- 

 tures ranging up to 30°C. However, if exposed to 

 the combined effects of a thermal shock (acclima- 



tion temperature not equal to test temperature), 

 and supersaturation, it is probable that a different 

 effect would be observed. 



ACKNOWLEDGMENTS 



Research on which this paper is based was 

 reported under Atomic Energy Commission Con- 

 tract Number AT(45-1)-1830. 



REFERENCES 



Anonymous. 1971. Columbia River Thermal Effects Study. 

 Volume 7: Biological Studies. Environmental Protection 

 Agency. In Cooperation with the Atomic Energy Commission 

 and the National Marine Fisheries Service. 102 pp. 



Fickeisen, D. H., M. ). Schneider and J. C. Montgomery. 1973. 

 Tolerance of Selected Fish Species to Atmospheric Cas Super- 

 saturation. American Fisheries Society 103rd Annual Meeting, 

 Orlando, Florida, September 10-12, 1973. BNWL-SA-4794. 



Weitkamp, D. E. and M. Katz. 1973. Resource and Litera- 

 ture Review of Dissolved Cas Supersaturation in Relation to 

 the Columbia and Snake River Fishery Resources. Report to 

 the Northwest Utilities Cooperative by Seattle Marine 

 Laboratories. 



74 Fickeisen, Montgomery, Hanf 



