E. M. Dawley 

 M. Schiewe 

 B. Monk 



Effects of Long- I 

 Term Exposure to 

 Supersaturation of Dissolved 

 Atmospheric Gases on Juvenile 

 Chinook Salmon and Steelhead 

 Trout in Deep and Shallow 

 Test Tanks 



ABSTRACT 



Bioassays in shallow (0.25 m) and deep (2.5 m) tanks with dis- 

 solved atmospheric gas concentrations ranging from 100 to 

 127% of saturation in water at 10°C were conducted to deter- 

 mine the lethal and sublethal effects on juvenile fall chinook 

 Oncorhynchus Uchawytscha and steelhead trout Sa/mo gairdneri. 

 Juvenile fall chinook (38.7 to 41.3 mm) were much more 

 resistant to supersaturation than juvenile steelhead (164 to 

 196 mm). Chinook tested in the shallow tanks at 120% of super- 

 saturation incurred 50% mortality after 22 days, whereas steel- 

 head tested at the same level incurred 50% mortality in 30 hr. 

 Gas bubble disease signs were noted on mortalities and on live 

 subsamples taken every 28 days. Vertical distribution of both 

 chinook and steelhead groups in the deep tanks appeared to 

 compensate for about 10% and 10 to 15%, respectively, of effec- 

 tive saturation. Average depths of the fish tested in deep tanks 

 increased with increased gas concentration. Significant differ- 

 ences in growth and condition factor were not found between 

 stressed and control fish during the test period. 



Effects of supersaturation of dissolved atmo- 

 spheric gases on freshwater fishes have been 

 studied by many investigators since the late 1800's. 

 The current problem of supersaturation in the 

 Columbia and Snake Rivers (Ebel, 1969; Beiningen 

 and Ebel, 1970; Ebel, 1971; Meekin and Allen, 1974) 

 has resulted in renewed interest in effects of super- 

 saturation on fish, and a great deal of research has 

 recently been accomplished by fisheries and other 

 agencies in the Pacific Northwest. Information on 

 the resistance of indigenous fish species to high 

 gas concentrations is well-documented for expo- 

 sure in shallow water for short periods of time 

 (Rucker and Tuttle, 1948; Harvey and Cooper, 1962; 

 Coutant and Genoway, 1968; Bouck, et al., 1970; Ebel, 

 Dawley, and Monk, 1971; Bouck, 1972; Blahrn, 

 McConnell, and Snyder, 1973; Fickeisen, et al., 1973; 



Dawley and Ebel, 1974) but there are still many un- 

 answered questions regarding the effects of chronic 

 low-level exposure on survival. Fish may be subjected 

 to low levels of supersaturation in two ways. They 

 may inhabit water areas where they cannot com- 

 pensate for gas saturation by sounding, or they 

 may inhabit deep water areas where hydrostatic 

 pressure offsets the effects of high gas levels. 



The National Marine Fisheries Service, funded 

 in part by the Environmental Protection Agency 

 (EPA) in 1972, began investigations of chronic 

 effects of long-term exposure of juvenile fall chi- 

 nook to various low levels of supersaturation. In 

 this report we describe those effects observed from 

 deep and shallow water tanks on juvenile fall chi- 

 nook salmon Oncorhynchus tschawytscha, and juve- 

 nile steelhead trout, Salmo gairdneri. 



MATERIALS AND METHODS 



Two bioassays of dissolved gas were conducted 

 at the Northwest Fisheries Center (Seattle, WA). The 

 first was completed in 1973 using fall chinook sal- 

 mon as the test animals, and the second in 1974 using 

 steelhead trout. Assays consisted of 20 simultaneous 

 tests of chinook and 18 simultaneous tests of steel- 

 head, in fresh water at 10°C, with various concen- 

 trations of dissolved gas in deep and shallow water 

 tanks. At termination of the tests, surviving fish 

 were divided into two groups; one group was trans- 

 ferred directly to salt water to assess the effects of 



Dawley, Schiewe. and Monk: National Marine Fisheries Service, 

 Seattle, Washington. 



