EFFECTS OF VARIOUS CONCENTRATIONS OF DISSOLVED ATMOSPHERIC 

 GAS ON JUVENILE CHINOOK SALMON AND STEELHEAD TROUT 



Earl M. Dawley and Wesley J. Ebel' 



ABSTRACT 



Bioassays in shallow tanks (25 cm deep) with dissolved nitrogen and argon gas concentrations ranging 

 from 100 to 125% of saturation in water at 15°C were conducted to determine lethal and sublethal 

 effects on juvenile chinook salmon, Oncorhynchus tshawyfscha, and steelhead trout, Salmogairdneri. 

 Significant mortality of both species commenced at 115% saturation of nitrogen and argon (111% 

 saturation of total dissolved atmospheric gas pressure). Over 50% mortality of both steelhead and 

 chinook occurred in less than 1.5 days in water at 120 and 125% of saturation. Significant differences in 

 swimming performance, growth, and blood chemistry were measured in groups of fish tested at 

 sublethal exposures in various concentrations of dissolved gases. Sublethal stress for 35 days at 110% 

 dissolved nitrogen (106% total atmospheric gas) decreased normal swimming ability of chinook. Growth 

 of both steelhead and chinook was affected by sublethal exposures in water saturated with atmospheric 

 nitrogen and argon at 105, 110, and 115%. Blood chemistry was affected at sublethal exposures in water 

 at 115% saturation. 



Supersaturation of atmospheric gas (mainly ni- 

 trogen) in waters of the Columbia and Snake 

 rivers-caused by spillway discharges from 

 dams— has been well documented as a serious 

 problem to valuable stocks of Pacific salmon, On- 

 corhynchus spp., and steelhead trout, Salmo 

 gairdneri. Gas bubble disease resulting from this 

 supersaturation causes both direct and indirect 

 mortalities. Direct mortality results from air em- 

 boli in the heart and gill filaments, destruction of 

 vital organs, or characteristic red blood cell 

 hemolysis (Marsh and Gorham 1905; Pauley and 

 Nakatani 1967; Bouck et al. 1970-). Indirect mor- 

 tality is a consequence of later invasion by disease 

 organisms (Coutant and Genoway 1968') or of 

 increased predation due to reduced performance 

 capabilities of the fish as the result of sublethal 

 exposure to supersaturation. 



The lowest level of nitrogen supersaturation at 

 which juvenile salmon or steelhead trout can be 

 exposed continually with no detrimental effects is 



'Northwest Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA. 2725 Montlake Boulevard East, Seattle, WA 98112. 



'Bouck, G. R., G. A. Chapman, P. W. Schneider, Jr., and D. G. 

 Stevens. 1970. Observations on gas bubble disease in adult 

 Columbia River sockeye salmon (Oncorhynchus nerka). Pac. 

 Northwest Water Lab. [Fed. Water Qual. Adm., Corvallis, Oreg.], 

 June 30, 1970. Unpubl. manuscr., 19 p. 



'Coutant, C. C, and R. G. Genoway. 1968. Final report on an 

 exploratory study of interaction of increased temperature and 

 nitrogen supersaturation on mortality of adult salmonids to U.S. 

 Bur. of Commercial Fisheries, Seattle, Washington. Battelle 

 Mem. Inst. Pac. Northwest Lab. Richland, Wash., November 28, 

 1968, 28 p. 



Manuscript accepted February 1975. 

 FISHERY BULLETIN: VOL. 73, NO. 4, 1975. 



not known. Several investigators have recorded 

 the lowest level observed during various 

 experiments where mortalities occurred from gas 

 bubble disease; however, very little attention has 

 been given to determining the effect of sublethal 

 exposure on physiological and behavioral perfor- 

 mance. Harvey and Cooper (1962) indicated 108- 

 110% saturation produced gas bubble disease and 

 subsequent mortalities in sockeye salmon alevins, 

 0. nerka; Rucker and Tuttle (1948) indicated a 

 level somewhere between 110 and 115% as being 

 the critical range for trout. Shirahata (1966) con- 

 ducted the most comprehensive study to date on 

 the effects of various levels of nitrogen gas on 

 rainbow trout (rainbow trout is the 

 nonanadromous form of 5. gairdneri, whereas the 

 steelhead trout is the anadromous) from hatching 

 to the swim-up stage, but such detail is lacking for 

 other species of salmonids. In many experiments 

 on gas bubble disease, either the water tempera- 

 tures, nitrogen gas concentrations, or life stages 

 of the test fish were omitted from record, thus 

 making the results incomplete for critical applica- 

 tions. 



Costs involved in alleviating the supersatura- 

 tion problem in the Columbia and Snake rivers will 

 be considerable. The extent of these costs will 

 depend on the degree of protection required to 

 afford a safe environment for the aquatic biota. It 

 is imperative, therefore, that regulatory measures 

 established to govern the level of saturation be 



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