DAWLEY and EBEL: EFFECTS OF DISSOLVED GASES ON SALMONIDS 



exhibited more than a 75% incidence of 

 exophthalmia, 20% of the fish had spinal flexures, 

 and 25% of the fish in section A became more or 

 less immobile. After 35 days of exposure at 110% 

 N2 +Ar, only 12% of the test fish exhibited signs 

 other than the lateral line bubbles. No apparent 

 signs of gas bubble disease were observed in fish 

 tested at 105% nitrogen. 



Development of gas bubble disease signs in 

 steelhead was similar to that of chinook-the signs 

 occurred in the same sequence but the exposure 

 time required to produce the signs was slightly 

 less. 



Recovery From Gas Bubble 

 Disease 



Observations on disappearance of gas bubble 

 disease signs and delayed mortality following 

 tests were made on groups of survivors of fish 

 stressed to the LE50 level at 120, 125, and 130% of 

 saturation. These survivors were placed in water 

 at 100% gas saturation for up to 15 days. No 

 delayed mortality could be attributed to prior ex- 

 posure to supersaturation in either the chinook or 

 the steelhead. The only significant mortality in 

 any recovery group was a 10% loss of one replicate 

 of steelhead subjected to 125% N2+ Ar until LEg^ , 

 followed by a burst swimming performance test. 

 Some mortality occurred after 102 h of recovery 

 time, but the only observable disease sign was the 

 presence of lateral line bubbles on one fish. Other 

 mortalities during recovery were less than 3% of 

 the fish held; no gas bubble disease signs were 

 found. All external symptoms that were readily 

 visible at the time the fish were removed from the 

 recovery tanks had disappeared after 15 days in 

 both species. 



Steelhead that had undergone 16, 24, and 35 

 days' exposure at 115% nitrogen saturation still 

 showed gas bubbles after being held 3 days in 

 normally (100%) saturated water. After 1.5 days' 

 recovery, 64% exhibited lateral line bubbles or fin 

 ray gas blisters and one fish (7%) retained 

 unilateral exophthalmia; after 2 days' recovery, 

 88% of another group retained signs of lateral line 

 bubbles and fin gas blisters; at 3 days, 54% of the 

 third group retained like signs of gas bubble 

 disease. After 15 days' recovery, no gas bubble 

 disease signs were observed on groups of test fish 

 examined. 



Effect of Supersaturation Stress 

 on Survivors 



Burst swimming performance and blood 

 chemistry were examined as potential indices of 

 stress from sublethal exposures to supersaturated 

 water. 



Swimming performance (Schiewe 1974) of 

 chinook that survived from tests at 110-125% was 

 significantly lower than that of control fish. Visual 

 observations of behavior during swimming per- 

 formance tests indicated genuine debilitation 

 (inability to swim in some cases) which in turn 

 resulted in lower swimming performance (i.e. less 

 distance gained and less swimming time against a 

 constant water current stimulus). No difference 

 was apparent between performance of chinook 

 salmon tested at 105% saturation and the control 

 fish. 



Swimming performance of steelhead trout that 

 survived tests at 105-125% was not significantly 

 different from the performance of control fish. 

 Performance of test and control lots of steelhead 

 trout was highly variable. Fish stressed by ex- 

 posure to supersaturation often responded in an 

 irritated or stimulated fashion, which often 

 resulted in a high measure of performance. 

 Further tests with steelhead are needed to deter- 

 mine whether swimming performance is a useful 

 index of stress from supersaturation and, if so, 

 whether test results in the laboratory apply to 

 survival of fish in the river. 



Blood serum from groups of chinook and 

 steelhead surviving supersaturation tests to LE^q 

 and LE50 were analyzed (Newcomb see footnote 

 6) using a SMA 12/60. A 5% decrease in serum 

 calcium was noted in chinook exposed to 115% ni- 

 trogen plus argon when compared to those exposed 

 to lower levels of supersaturation. Steelhead ex- 

 posed to 115% nitrogen showed a 10 to 17% 

 decrease in serum calcium and a decrease in serum 

 albumin, total protein, serum chloride, cholesterol, 

 and in alkaline phosphatase activity when com- 

 pared to controls and those exposed to lower sat- 

 urations. No significant changes in blood serum 

 components were observed in samples taken from 

 test groups exposed to levels of 105 and 110% of 

 saturation when these were compared with con- 

 trols. 



Measurements of photic response of salmonids 

 failed to provide any consistent evidence of 

 stress-related phenomena due to supersaturation 

 so these tests were discontinued. 



793 



