effect of reduced oxygen on the mortality rate. This 

 was apparent in the experiment using 173% O2 and 

 105% N 2 . At 173% 2 there were losses of 26% and 

 30% in 39 days, whereas slightly larger fish at the 

 lower end of the troughs subjected to 169% O2 had 

 losses of only 7% in 39 days. 



PATHOLOGY 



Generally, the fish died quite suddenly in the 

 higher nitrogen concentrations. Never was tissue 

 damage or any progressive pathology demonstrated. 

 The fish always seemed to die from gas embolism 

 restricting the flow of blood through the gills. When 

 the nitrogen was near normal and the oxygen quite 

 high, the fish were moribund for many days before 

 succumbing. These fish had blebs in the mouth 

 which interfered with feeding and caused 

 emaciation. 



SUMMARY 



Coho salmon fingerlings were subjected to a 

 total gas pressure of 119% at 13.6°C with the O2/N2 

 varying from 50%/138% to 229%/90%. The small 

 fish (3.8 to 6 cm) were the most resistant and the 

 larger fish (8 to 10 cm) the least resistant to gas 

 bubble disease at the gas concentrations used. A 

 drastic decrease in lethal effect of individual ratios 



of O2 to N2 occurred between 159% O 2 /109% N 2 and 

 173% 02/105% N 2 at the same total gas pressure 

 (119%). 



ACKNOWLEDGMENTS 



Facilities for this work were furnished by the 

 Western Fish Disease Laboratory, Bureau of Sport 

 Fisheries and Wildlife, Seattle, Washington. The 

 work was started when the author was an employee 

 of this organization. 



The pathology was studied by William T. 

 Yasutake, pathologist, Western Fish Disease 

 Laboratory. 



REFERENCES 



Anonymous. 1974. Total dissolved gases (supersaturation). In: 

 Water Quality Criteria. National Academy of Science Publica- 

 tion. (In press) pp. 135-139. 



Meekin, T. K. and B. K. Turner. 1974. Tolerance of Salmonid 

 Eggs, juveniles, and Squawfish to Supersaturated Nitrogen. 

 Wash. Dept. Fish., Tech. Rpt. No. 12, pp. 78-126. 



Rucker, R. R. 1972. Gas Bubble Disease of Salmonids: A 

 Critical Review. Technical Papers of the Bureau of Sport 

 Fisheries and Wildlife. Number 58. 11 pp. 



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. To North- 

 west Utilities Cooperative. 55 pp. 



88 Rucker 



