FISHERY BULLETIN: VOL. 73, NO. 4 



Figure 3. -Gas bubbles (arrow) in 

 lateral line of juvenile chinook sal- 

 mon. 



Progression of Gas Bubble Disease 



Observations on the progression of external 

 signs of gas bubble disease in spring chinook ex- 

 posed to various levels of supersaturation revealed 

 that the first developments such as bubble forma- 

 tion in the lateral line (Figure 3) appear within 2 h 

 of exposure at 125%. Subcutaneous gas blisters 

 between fin rays of at least one fin were present on 

 each of the test animals before 11.5 h at 125%, and 

 before 55 h at the 120% level. Several days' ex- 

 posure were required before these signs occurred 



on fish tested at 115%. After 35 days, 56% of the 

 fish at 110% had lateral line bubbles but only 4% 

 had fin bubbles. Exophthalmia or "popeye," 

 hyphema, cutaneous blisters of the head and buc- 

 cal cavity, and spinal flexures were absent among 

 fish tested at 120 and 125% but began appearing 

 after 6 days on fish held at 115% and after 11 days 

 on those held at 110% of nitrogen saturation. Ap- 

 parently at the higher saturation levels, the fish 

 died from cardiac occlusion or branchial artery 

 occlusion (Figure 4) before development of these 

 signs. By the end of 35 days, fish held at 115% 



Figure 4.-Gas emboli occluding gill 

 filaments and branchial artery of 

 chinook salmon held in 125% nitrogen 

 saturation for 20 h. 



792 



