TABLE 1 Test I, Percent Cumulative Mortality Due to Gas Bubble Disease in juvenile Chinook 

 Salmon Exposed to 119% to 123% Supersaturation at Rock Island Forebay, May 24 to June 3, 1974. 



Holding 

 time 



(days) 



Cage depth (meters) 



1-2 m and 3-4 m' 



0-4 m 0-3 m 0-2 m 0-1 m 



1-2 m 



2-3 m 



3-4 m 



|16 J, 8 f 12 4,12 f8 ;16 



1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 



1 

 2 

 4 

 14 

 21 

 23 

 35 

 42 

 53 



Survivors 

 with GBD 

 lesions (%) 



90 



15 



| indicates hr/day at 1-2 m depth, [ indicates hr/day at 3-4 m depth. 



Most of the surviving fish with evidence of 

 GBD were placed in the 3 to 4 m cage to determine 

 if they could recover. A few of the severely affected 

 fish died before the cage was submerged. The 

 remainder were held as part of the second experi- 

 ment. All surviving fish with no indication of GBD 

 were released in the Rock Island forebay. 



Test II 



The total dissolved gas saturation of the river 

 water at the beginning of the second test (June 5) 

 was down to 120% (Fig. 5) as measured at the test 

 site. By the 4th day (June 9), the gas. saturation had 

 risen to 122%, and remained constant until the 

 10th day when it rose to 123%. During the last 

 11 days (June 15 to 25) of the test, the saturation 

 varied between 123% and 126%. 



The water temperatures at the beginning of the 

 second test remained near 10.7°C for the first 

 3 days. During the remainder of the test the water 

 temperatures showed a steady increase of about 

 0.2°C per day, reaching 14°C by the end of the test. 

 The light penetration decreased considerably dur- 

 ing the last half of the second test. For the first 

 8 days, the Secchi disc readings ranged from 0.91 m 

 to 1.22 m. During the last half of the test, Secchi 

 disc readings decreased to 0.33 to 0.61 m. 



Two fish were lost at the beginning of this test, 

 apparently due to handling stress. The other test 

 fish showed no signs of GBD at the time of these 

 mortalities. The mortalities occurring due to GBD 

 during the second test did not begin until the 6th 

 day. As in the previous test, mortalities occurred 



28 Weitkamp 



first in the to 1 m cage (Table 2). The daily mor- 

 ality rate in Test II (Fig. 5) was similar, but not as 

 consistent as that of Test I. The rate at which mor- 

 talities occurred in the to 1 m cage between 



FIG. 5 Test II, total dissolved gas levels and % cumulative 

 mortalities greater than 1% for all cages, June 5-25, 1974. 



