Gas Bubble Disease 



When excessive amounts of dissolved nitrogen are pre- 

 sent, fish develop gas bubble disease (fig. 41). It causes 

 bubbles under the skin, in the roof of the mouth, or in fin 

 membranes; it also produces a "pop-eye" condition (hem- 

 orrhaging in the eye). Supersaturation of nitrogen occurs 

 in turbulent water below spillways or where the water warms 

 rai)idly without adequate circulation. The condition is com- 

 pounded by high water temperatures. Fish supersaturated 

 with nitrogen have lower tolerance for higher temperature. 



Potentially dangerous concentrations of dissolved nitrogen 

 (over 110 percent) are reached in the Columbia River in 

 spring and summer. Excessive numbers of juvenile salmon 

 died in holding tanks at The Dalles Dam. The danger is 

 not so great if the fish dive, but they are not always in an 

 area with sufiicient depth. One experiment showed that 

 at nitrogen saturation of 130 to 140 percent, coho and chinook 

 salmon must remain in more than 8 feet of water if they 

 are to be free of the symiitoms of gas bubble disease. 



Tlie disease could be reduced by control of spilling during 

 downstream migration. When the river flow becomes al- 

 most completely controlled by dams, and spilling is nearly 

 eliminated, the problem is expected to diminish. 



FISH BEHAVIOR 



In their field studies, biologists often suspect that spe- 

 cific environmental conditions may influence the behavior 

 or survival of fish. These conditions may be duplicated or 

 altered in the laboratory. The responses to lieat, light, pres- 

 sure, shear forces, cavitation, and changes in flow as well 

 as the periodic activities of fish were observed at our be- 

 havior laboratory in Seattle. 



Heat 



Fish migrating downstream could abruptly enter heated 

 water from nuclear power plants and be unable to escape 



IIVIETRIC 1 



FIGURE 41.— Gas bubble in eye tissue of coho salmon. 



before being overcome by the high temi)erature. To sim- 

 ulate the efl^ect of their contact with heated water pouring 

 out of such plants, yearling coho salmon were subjected 

 to sudden increases in water temperature. Test fish ac- 

 climated to 50° F. died within 50 seconds of exposure to 

 90°, believed to be close to the temperature of heated dis- 

 charges. 



Light 



Lights placed near gatewells and near the ceiling of a sim- 

 ulated turbine intake caused more fish to enter the gatewells. 

 The fish, like moths, seemed to be attracted. 



Pressure 



Responses to change in hydrostatic pressure were meas- 

 ured. Coho and sockeye salmon fingerlings swam actively up- 

 ward when ]iressure increases were equivalent to depth 

 increases of less than 2 feet (fig. 42) . This behavior suggests 

 that fish may be collected more readily by taking advantage 

 of their tendency to compensate for change in pressure. 



31 — 



