wo 



SO 



"> 60- 



40 



45 60 90 



EXPOSURE TIME (MINUTES) 



120 



FIC. 3 Preliminary results of internally and externally com- 

 bined supersaturations. Exposure time indicates the length of 

 time the fish were maintained at depth (100 ft only in these 

 tests) before decompression. Zero, 5, and 15 min indicate the 

 length of time the fish were held in supersaturated water after 

 decompression. Most data points represent 30 fish (10 fish x 3 

 tests) and ranges are indicated by vertical broken lines. Where 

 no vertical lines appear, only one test was conducted and N 

 = 10 fish. 



separate procedures* and the combination of the 

 two is somewhat more effective than either taken 

 alone. Use of these different procedures explains 

 the anomaly between human diving physiology 

 and the problems fish encounter naturally. It is 

 the internal saturation that parallels human diving 

 decompressions. The interesting and significant 

 difference between man and fish is that fish of 

 this size are actually more tolerant of supersatura- 

 tion (400 versus 200%) than are humans. As long as 

 a fish is allowed the opportunity and sufficient time 

 to eliminate the gas, it can survive high internal 

 supersaturation. 



The fish has no opportunity to eliminate gas 

 when either exposed to external supersaturation 

 or exposed simultaneously to internal and exter- 

 nal supersaturation. Thus, the effects of the latter 

 treatment are synergistic. Furthermore, the bubbles 

 do not necessarily have to be found throughout the 

 fish, nor does the fish have to be anywhere near 

 fully saturated; bubbles in the coronary arteries 

 are sufficient to cause death. 



To summarize our studies and put the results 

 into perspective, several statements can be made: 



1. Equilibration of highly perfused tissues of 

 coho salmon (60-100 mm) occurs in 60 to 90 min 

 at any saturation. Therefore, below a certain satu- 



ration level (less than 150%) mortalities cannot be 

 directly related to equilibration time only because 

 death in these chronic tests occurs hours or even 

 days after equilibration is reached. The total 

 amount of gas necessary to cause mortality is a 

 critical factor but it is unclear at this time what 

 other factors are involved in the chronic tests. 



2. Fish can withstand high supersaturations 

 for short periods as long as they are able to elimi- 

 nate the excess gas. 



3. Depth is critical in keeping gas in solution. 

 If a fish in a river sounds he can redissolve bubbles. 

 Water often has the same gas concentration 

 throughout the water column (due to turbulent 

 mixing). Therefore, a sounding fish may redis- 

 solve the bubble, but will not be able to eliminate 

 the gas and will still be supersaturated on surfac- 

 ing again. If, however, the fish (at the surface) 

 swims into an area of non-supersaturated water 

 (e.g., another stream) he can desaturate quite 

 easily although some sublethal effects may be 

 incurred due to the previous supersaturation (e.g., 

 fish that we have exposed to sublethal supersatura- 

 tions are extremely susceptible to disease). If the 

 fish stays at depth all of the time, no bubbles 

 should appear. 



FUTURE STUDIES 



The main emphasis in our future studies will 

 be to investigate further the relationship of gas 

 saturation rates and bubble formation to different 

 sizes, temperatures, activity rates, and other gases; 

 resolve the differences between our acute test 

 results and chronic tests (the time lag): and explore 

 the additional mechanisms (blood clotting, etc.) 

 that could be related to this time lag. 



ACKNOWLEDGMENTS 



Supported by National Institute of Health 

 Grant #HL 16254-02. 



REFERENCES 



Ackles, K. N., ed. 1973. Blood Bubble Interaction in Decom- 

 pression Sickness. Def. and Civil Inst. Envir. Med. Proc, 302 pp. 



Marsh, M. C. and F. P. Gorham. 1905. The gas disease in 

 fishes. In: Report of the Bureau of Fisheries, 1904, pp. 343-376. 



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

 eggs, juveniles, and squawfish to supersaturated nitrogen. In: 

 Nitrogen Supersaturation Investigations in the Mid-Columbia 

 River. Wash. Dept. Fish., Tech. Rpt. 12, pp. 87-88. 



U.S. Navy. 1973. U.S. Navy Diving Manual (Vol. 1), 

 NAVSHIPS 0994-001-9010. Washington, D.C. 



•Temperature-induced bubbles will be examined in future 

 studies. 



50 Beyer, D'Aoust, Smith 



