Thirty marked fish from each family were put 

 into each of three tanks (1.8 m in diameter and 0.3 

 m deep) at the Abernathy Center. These groups of 

 30 fish will be referred to as tank-families. The 

 remaining 10 fish from each family were put into a 

 similar tank as a control. The test tanks were 

 supplied with 18.9 liter/min of water which was 

 air-supersaturated to 130 +. 1.5%. 



Two variables, time to death for each fish after 

 exposure to air-supersaturated water and the 

 percentage survival for each family after 36 h of 

 exposure, were examined. 



Water to be air-supersaturated was directed in- 

 to a pump to create a line pressure of 1.4 kg/cm-. A 

 controlled amount of air was injected into the line 

 through an air stone inserted at a joint in the line. 

 Aeration occurred under pressure in a 1.5-m ver- 

 tical section of line. The test water then entered a 

 pressurized tank where excess air was vented. 

 Air-supersaturated water from the pressure tank 

 was then jetted below the surface into the test 

 tanks. 



Stock Comparisons 



Since differences between stocks of fish in their 

 resistance to gas-bubble disease arise from both 

 genetic and environmental factors, the fish used in 

 the present experiments were reared in one loca- 

 tion under controlled conditions to minimize 

 differences related to environment. Differences in 

 the groups of fish tested then were assumed to 

 have a genetic basis. 



Locations on or near the Columbia River that 

 are discussed in this report are the following 

 approximate distances (kilometers) upstream 

 from the Pacific Ocean: Abernathy Salmon Cul- 

 tural Development Center, 72; Kalama Hatchery, 

 105; Bonneville Dam, 234; Little White Salmon 

 Hatchery, 265; Little Goose Dam, 635. 



Experiment L-In the fall of 1972, eggs were 

 taken from mature fall chinook at Little Goose 

 Dam on the Snake River, and at Trask River Salm- 

 on Hatchery. Smolts migrating downstream 

 from Little Goose Dam must pass over seven dams 

 and swim through water which may be air-super- 

 saturated up to 130% (Beiningen and Ebel 1971). 

 The Trask River enters the Pacific Ocean about 80 

 km south of the Columbia River and has never 

 been known to contain lethal levels of air-super- 

 saturated water. Eggs obtained at the Trask River 

 Salmon Hatchery were taken from a large number 



of crosses, and eggs obtained at Little Goose Dam 

 were from crosses between two males and two 

 females. 



Fertilized eggs from each source were trans- 

 ported to Oregon State University where they 

 were incubated at 9.5°C. The fry were fed for 2 mo 

 before being exposed to 127% air-supersaturated 

 water. At the time of testing, the fish weighed 

 between 1.3 and 1.5 g. 



Air-supersaturated water was produced by 

 aerating water under a hydrostatic head of 3 m in 

 a vertical column of 15.2-cm pipe. A regulated 

 amount of air was injected into the lower portion 

 of the column through four air stones. Water 

 drawn from the bottom of the column was 123% 

 air-supersaturated. This water was then heated to 

 13.5°C to attain the test level of 127 + 2% super- 

 saturation. 



Experiment IL-In 1973, fall chinook eggs were 

 obtained from Abernathy Salmon Cultural 

 Development Center, Little White Salmon 

 Hatchery, and Kalama Hatchery-all on the 

 Columbia River-and from the coastal Trask River 

 Salmon Hatchery. Eggs from fish at Columbia 

 River hatcheries were taken on 2 October, and 

 those from fish at Trask River Hatchery on 28 

 November. All eggs were taken to Oregon State 

 University for incubation, rearing, and testing. 



Because of differences in ages, the experimen- 

 tal groups had to be tested at different times. W^e 

 held the test fish in a constant environment at 

 equal densities during the rearing period. The 

 fingerlings were reared at 13.5°C in a 5.2 m x 0.3 m 

 X 0.3m Plexiglas^ tank which was divided into 16 

 sections. The sections were divided into four 

 blocks of four tanks each. Fifty fish from each of 

 the four stocks were put into one section in each of 

 the four blocks establishing a randomized block 

 design. Fish were reared for 50 days, at the end of 

 which time they weighed from 1.0 to 1.7 g. Seven 

 days before testing, each group of fish was marked 

 with a group-specific cold brand. 



The fish were exposed to 127 +. 2% air-supersa- 

 turated water at 11 °C in a 16.5-liter tank. Time to 

 50% mortality, proportion dead in 96 h, and 

 proportion dead in 150 h were determined. An ap- 

 paratus similar to that described above for tests at 

 the Abernathy Center was used in this 

 experiment. In all tests, we measured the total 



-Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



935 



