FISHERY BULLETIN: VOL. 73, NO. 4 



based upon a thorough understanding of the ef- 

 fects of dissolved gases on aquatic organisms. 



This paper describes the results of dissolved gas 

 bioassays with juvenile steelhead trout and spring 

 Chinook salmon, 0. tshatvytscha, conducted by the 

 National Marine Fisheries Service during the 

 spring of 1972. These experiments were designed 

 to assess lethal and sublethal effects of supersat- 

 uration of atmospheric gases on test fish at levpls 

 found in the Columbia and Snake rivers during the 

 spring freshet. Atmospheric nitrogen concentra- 

 tions' were of major concern and test levels ranged 

 from 100 to 125% of saturation. Special note is 

 made of testing procedures and ramifications of 

 the effects of these on the outcome of our tests. 



METHODS 



Bioassays were carried out in the laboratory in 

 shallow tanks (25-cm water depth) to negate the 

 effects of hydrostatic pressure compensation. 

 These facilities were similar to those described by 

 Ebel et al. (1971). Water flow into each test tank 

 was maintained at 3 liters/min at a temperature of 

 15° ± 0.5°C. Test tanks were partitioned with 

 perforated fiberglass plates to form four sections 

 — in-flow area, test area A, test area B, and out- 

 flow section (Figure 1). 



Supersaturated water was produced by meter- 



'Atmospheric nitrogen-nitrogen gas (98.8% by vol) plus argon 

 gas (1.2% by vol) hereafter referred to as nitrogen or N2 + ^'^■ 



ing 0.7 liter/min air into the suction side of a cen- 

 trifugal pump which recirculated water through a 

 197-liter (52-gallon) closed receiver at a rate of 

 about 190 liters/min (50gal/min). Water pressure 

 throughout the system was at 1.4 kg/cm- (20 psi) 

 except in a short section of pipe on the discharge 

 side of the pump where it was increased to 3.2 

 kg/cm- (45 psi) by use of a valve for additional 

 back pressure necessary to achieve the required 

 supersaturation. Water remained in the recircula- 

 tory system for about 10 min before passing to the 

 test tanks. This arrangement supersaturated the 

 water to about 145% of air saturation. Water was 

 then piped to the test tanks where it passed over a 

 series of perforated fiberglass plates into an inlet 

 box with air bubbling through a bottom plate of 

 porous polyethylene. The number of fiberglass 

 plates and volume of air were adjusted to yield the 

 various levels of saturation. An increase of air to 

 water interface directly decreased the excess dis- 

 solved gas content. 



Water samples for dissolved gas analyses were 

 collected throughout the tests near the center of 

 each test tank directly in front of the partition 

 between A and B testing areas and in some tests 

 at the center of each section of the tank. 

 Frequency of analysis varied from once an hour to 

 once a day depending on duration of test. 

 Procedure for analysis of dissolved nitrogen was 

 from Van Slyke and Neill (1924) using manometric 

 blood gas apparatus; dissolved oxygen was 

 analyzed using modified Winkler procedures 



Vinyl air supply 

 tube 



-50 cm 



-50em- 



-124cm 



PLAN VIEW 



Supersoturoted 

 constant-temperature 

 water source 



Oiilesj air ^ 

 supply 



j( .1 Mechonicol woter equilibrotor 



. -^ f with adjustoble fiberglass 



'or 

 ilo 



24cm 



Perforated fiberglass 

 plates 



Trar)slucent riberglass 

 cover 



Figure L-Pian and cross-sectional views 

 of test tank used for bioassay of dissolved 

 gas. 



35cm 



Polyethylene plote ^ Air bubbling 



porous to air ^g,^, equilibrotion 



CROSS SECTION 



788 



