6 to 16 percent of the coho and chinook salmon died 

 in a pen whicli allowed the fish to seek any depth 

 from the surface to 6 m., which suggested that 

 some mortality may also have occurred to naturally 

 migrating fingerlings even though they could move 

 to any depth. 



These field observations of juvenile migrants, 

 though limited, indicate that naturally migrating 

 juvenile fish in the Priest Rapids Dam area ai*e 

 under stress from supersaturation of dissolved 

 nitrogen; it is highly probable that a significant 

 percentage of the fish is lost. The Hanford area of 

 the ri\ier downstream from Priest Rapids is of 

 particular concern. Juvenile and adult salmon al- 

 ready under stress must pass areas where thennal 

 reactors emit large volumes of water with tem- 

 peratures 10° to 15° C. higher than the river 

 temperatures, ()b^•iously, fish under stress from 

 supersaturation of gases have less tolerance to 

 rapid temperature increases, and losses of fish 

 which inadvertently enter the thermal plumes are 

 inevitably high. Further investigation seems im- 

 perative on the effect of supersaturation of dis- 

 solved nitrogen on the tolerance of salmon to 

 temperature increases. 



ADULT SALMON AND STEELHEAD TROUT 



About 2,300 adult chinook salmon, 1,600 .steel- 

 head trout {tSalmo gainhieri), and 1,000 sockeye 

 salmon {Oncorhynclms nerha) were examined at 

 Bonneville and McNary Dams from mid-April 

 through mid-October 1967 for external symptoms 

 of gas bubble disease. The external symptoms that 

 were used to indicate gas bubble disease were (1) 

 gas bubbles under skin, in roof of mouth, and in 

 fin membranes and (2) hemorrhaging inside the 

 eye and the associated "pop eye" condition of the 

 eyeball. Nitrogen saturation was measured at both 

 dams so that the incidence of disease symptoms 

 could be correlated with the saturation of nitrogen. 



Examination of the adult salmon and steelhead 

 trout began on April 11 when saturation was about 

 106 percent and continued until May 25 when sat- 

 uration was near 120 percent. Because nitrogen 

 saturation did not exceed 110 percent until May 

 10, little incidence of gas bubble disease -was ex- 

 pected; 1 of 125 steelhead trout examined showed 

 symptoms of the disease (on May 25). 



Observations of adult fish at McNary Dam be- 

 gan on June 23 and ended October 11. Nitrogen 



saturation ranged from 131 percent in June to 104 

 percent in October. Saturation was high (above 

 120 percent) from June 23 to July 19 but began 

 to drop sharply after July 19 ; by August 22, val- 

 ues were below 110 percent. In July, symptoms of 

 gas bubble disease were noted in 10 of 1,000 sock- 

 eye salmon, but none were observed in 1,762 

 chinook salmon and 1,461 steelhead trout. Ap- 

 parently, chinook salmon and steelhead trout in 

 this area either compensated for the high satura- 

 tion by remaining at a sufficient depth or the 

 symptoms of the disease had not progressed suffi- 

 ciently to be evident. 



Surveys for carcasses of adult fish were made 

 from April to October during each flight made to 

 obtain water samples. Four additional aerial sur- 

 veys for carcasses were made during June and 

 July when saturation was highest. Carcasses of 

 eight dead salmon (and a few unidentified fish) 

 were deserved; however, it could not be positively 

 verified that any of these fish had died from gas 

 bubble disease. Generally, the fish were too decom- 

 posed for determination of cause of death. 



Steelhead trout and chinook salmon were ob- 

 served (June 15 to September 19) congregating in 

 the Columbia River at its confluence with the 

 Snake River. Saturation of dissolved nitrogen in 

 the Columbia ranged from 110 to 130 percent, and 

 temperatures in the Snake River were as much as 

 5.7° C. (10.3° F.) higher than in the Columbia 

 (table 4). Fish equilibrated to supersaturation of 

 dissolved nitrogen in the Columbia could have died 

 fi-om gas embolism if they had entered the Snake 

 River at this time. A concentrated search on the 

 surface by boat and on the bottom with SCUBA 

 did not yield carcasses of any salmon whose death 



Table 4. — Temperature (° C.) and percentage saturation of 

 dissolved nitrogen in the Columbia and Snake Rivers at 

 the mouth of the Snake River — June 6 to Sept. 5, 1967 



10 



U.S. FISH AND WILDLIFE SERVICE 



