Table 2.— Hours to 50% mortality (ET^q), and percentages dead 

 in 96 h (P96) and 150 h (P150) for juvenile chinook salmon exposed 

 to air-supersaturated water in Experiment II. Each value 

 represents an average of four replicates; ranges are shown in 

 parentheses. 



Table 3.-Analysis of variance in time to 50% mortality for Trask 

 and Columbia River chinook salmon (Experiment II). 



Stock 



ET, 



P96 



P150 



Abernathy 



Little White Salmon 



Kalama 



Trask 



92.5 (70-116) 



86.5 (82-94) 



73.8 (64-79) 



62.0 (48-75) 



53 

 61 

 64 

 70 



(43-64) 

 (57-67) 

 (60-70) 

 (64-82) 



68.5 (63-80) 



77.0 (75-80) 



86.0 (73-95) 



86.8 (75-96) 



significant (Table 3). Variation between the three 

 Columbia River stocks was not significant. 



Similar comparisons were made from data 

 summarized after 96 and 150 h of exposure (Table 

 2). On the average, differences between Columbia 

 and Trask stocks remained significant, but varia- 

 tion between Columbia River stocks became sig- 

 nificant only after 150 h of exposure {F = 5.01). 

 This difference was between the Kalama stock 

 and other lower Columbia River stocks, suggest- 

 ing that a difference in resistance to gas bubble 

 disease exists even between stocks separated by 

 relatively short distances. The reason for the 

 similarity of resistances between lower Columbia 

 River stocks probably was their common origin: 

 Abernathy brood stock were originally taken from 

 Spring Creek and Willard hatcheries, both of 

 which are located upstream from Bonneville Dam. 



The much greater difference in time to 50% 

 mortality between fish taken from Little Goose 

 Dam and fish from the Trask River (80.5 + 3.39 h) 

 than between combined lower Columbia stocks 

 and the Trask stock (22.25 ± 6.37 h) indicates that 

 fall chinook salmon migrating as far as Little 

 Goose Dam are more resistant to gas bubble 

 disease than are lower Columbia River stocks. This 

 conclusion could be made only by comparing 

 results from Experiments I and II, and by assum- 

 ing that the results were not biased by the small 

 number of crosses made at Little Goose Dam. 



Discussion 



Differences between stocks indicated that 

 selection for phenotypes with greatest resistances 

 to gas bubble disease has occurred in the Columbia 

 River. This conclusion was supported by the ob- 

 servation that stocks with the longest histories of 

 exposure to air-supersaturated water were most 

 resistant to gas bubble disease. 



Because additive genetic variance contributing 

 to the observed differences probably has been 

 reduced, and reduced at an unknown rate, it is 



Source of variation 



Degrees of 

 freedom 



Mean 

 squares 



*, **, statistical significance at the 0.05 and 0.01 levels, re- 

 spectively. 



impossible to estimate accurately the selection in- 

 tensities that must have occurred in the past to 

 produce the differences in resistance observed 

 between Trask and Columbia River stocks. The 

 low heritability for resistance to gas bubble 

 disease in fall chinook salmon indicates that no 

 great increases in resistance can be expected even 

 at relatively high selection intensities. 



The results further indicate that stocks trans- 

 ferred from coastal streams to hatcheries within 

 the Columbia River drainage may experience high 

 levels of mortality from gas bubble disease. On the 

 other hand, Columbia River stocks may provide a 

 source of brood fish that are resistant to gas bubble 

 disease for stocking in other waterways. 



Acknowledgments 



We thank Director Bobby Combs and personnel 

 at the Abernathy Salmon Cultural Development 

 Center and personnel at the various locations from 

 which eggs were obtained. The manuscript 

 benefitted from reviews by P. H. Eschmeyer, J. A. 

 Lichatowich, and an anonymous reviewer. 



Literature Cited 



Bartlett, M.S. 



19.36. The square root transformation in analysis of 

 variance. J. R. Stat. Soc. (Suppl.) 3:68-78. 

 Beiningen, K. T., and W. J. Ebel. 



1971. Dissolved nitrogen, dissolved oxygen, and related 

 water temperatures in the Columbia and lower Snake 

 Rivers, 1965-69. U.S. Natl. Mar. Fish. Serv. Data Rep. 56, 

 60 p. 

 Blahm, T. H., R. J. McConnell, and G. R. Snyder. 



1975. Effect of gas supersaturated Columbia River water on 

 the survival of juvenile chinook and coho salmon. NOAA 

 Tech. Rep. NMFS SSRF-688, 22 p. 



DiCKERSON, G. E. 



1959. Techniques for research in quantitative animal 

 genetics. In Techniques and procedures in animal 

 production research, p. 56-105. Am. Soc. Anim. Prod., 

 Beltsville, Md. 



937 



