A. On lateral line and body. 



B. Protruding eyes. 



C. On head and operculum. 



Figure 4.— Examples of external symptoms of gas-bubble 

 disease as noted throughout the experiment. 



conditions that prevailed in the Columbia River dur- 

 ing the test period were closely reflected in the test 

 tanks. However, variations did occur in river water 

 quality conditions and the control tank. A summary 

 of the maximum average differences throughout the 

 test in water quality data between the river and the 

 holding tanks is given in Table 3; comprehensive data 

 can be found in Appendix Tables 1 through 4. 



In this report nitrogen gas saturation is discussed 

 with more detail than other types of quality 

 parameters because it was used as the index to which 

 fish mortality was related. 



Control tank. — In this tank the concentration of 

 nitrogen gas was near 100% of saturation; however, on 

 one occasion during the test period 109% of saturation 

 was recorded. Of the 61 daily samples taken, 52 (85%) 

 fell between 97 and 106% of saturation. 



BUBBLE 



D. In mouth. 



