FIG. 13 Eroded caudal iin and fungal growth typical of fish that 

 did not recover from gas bubble disease. 



area of the gills and eyes or no signs of GBD. Some 

 of the mortalities still showed bubbles in the roof of 

 the mouth although all other external indications 

 of GBD had disappeared. 



The loss of only about 10% of the fish with GBD 

 in the recovery cage indicates most of the fish 

 showing GBD lesions are able to survive and re- 

 cover within a 20-day period. This recovery appears 

 to be complete in most cases. Only 9% and 5% of 

 the fish in the recovery cage of Tests II and III, 

 respectively, showed any indication of GBD after 

 20 days. This experiment indicates recovery of the 

 majority of fish with GBD lesions when they are 

 subjected to increased water pressure. It is not 

 known if the same effect would be derived by plac- 

 ing the sick fish in saturated water at the same 

 depth or pressure as they occupied when they 

 acquired the disease. No attempt was made to 

 correlate survival with the severity of the GBD 

 lesions at the beginning of these tests. The presence 

 of hemorrhages in some of the survivors from the 

 recovery cage is an indication that some of the fish 

 that began the test with severe signs of GBD had 

 lost some of the signs of GBD and recovered and 

 survived for 20 days. 



Previous Live Cage Studies 



The results of this live cage study are quite 

 similar to the results of Meekin and Turner (1974). 

 Meekin and Turner tested juvenile chinook in river 



water with nitrogen supersaturation at 124% and 

 an oxygen supersaturation of 117% (about 120% 

 total dissolved gas). In their study most fish held 

 within 0.61 m (2 ft) at the surface died with GBD 

 lesions within 7 days. Juvenile chinook held at 

 1.52 to 2.13 m (5 to 7 ft) for 14 days had few mor- 

 alities (4 to 16%) and the fish held at 2.44 to 3.05 m 

 (8 to 10 ft) had no mortalities or survivors with 

 GBD lesions. 



Ebel's Priest Rapids (1967) and Ice Harbor (1971) 

 live cage studies indicated juvenile chinook must 

 remain below 2.5 m to be free of GBD symptoms. 

 The difference between Ebel's results and the re- 

 sults of this study appear to be due to the higher 

 levels of supersaturation experienced in Ebel's 

 studies. In Ebel's studies nitrogen supersaturation 

 reached 127% to 143% during the various tests. 

 These higher nitrogen supersaturations would 

 provide total dissolved gas saturations of about 

 125% or higher. The higher supersaturations in 

 Ebel's tests would account for the greater mor- 

 talities, according to the more severe effects of 

 supersaturations of 125% and higher indicated by 

 our 1974 study. 



REFERENCES 



Ebel, W. J. 1969. Supersaturation of nitrogen in the Columbia 



River and its effect on salmon and steelhead trout. Fish. Bull., 



68:1-11. 

 Ebel, W. J. 1971. Dissolved Nitrogen Concentrations in the 



Columbia and Snake Rivers in 1970 and Their Effect on 



Chinook Salmon and Steelhead Trout. NOAA Tech. Report 



SSRF-646, 7 pp. 

 Egusa, S. 1959. The gas disease of fish due to excess of 



nitrogen. Hiroshima U.Jour. Fac. Fish. An. Husb., 2:157-182. 

 Leman, B. 1971. A Discussion of Nitrogen-Supersaturation 



of Columbia River Water in Relationship to Basic Phenomenon 



and the Physical Laws of Cases. Presented at the Association 



of Power Biologists Conference, Sept. 22, 1971, Wenatchee, 



Washington, Unpublished. 

 Meekin, T. K. and B. K. Turner. 1974. Tolerance of Salmonid 



Eggs, juveniles, and Squawfish to Supersaturated Nitrogen. 



Wash. Dept. Fish., Tech. Rpt. 12, pp. 78-126. 

 Pauley, G. B. and R. E. Nakatani. 1967. Histopathology of 



"gas bubble" disease in salmon fingerlings. jour. Fish. Res. 



Bd.', Can., 24:867-871. 

 Rucker, R. R. and K. Hodgeboom. 1953. Observations on gas 



bubble disease of fish. Prog. Fish. Cult., 75:24-26. 

 Rukavina, J. and D. Varenika. 1956. Air bubble disease of 



trout of the source of the river Bosna. Acta Icbthyologica 



Bosniae et Hercegovinae, Editum 1, x(7):5-12 (from Renfro, 



1973). 

 Shirahata, S. 1966. Experiments on nitrogen gas disease 



with rainbow trout fry. Bull. Fresh. Fish. Res. Lab., 15(2): 



197-211. 



36 Weitkamp 



