Biological Studies: I 

 Laboratory 

 Orientation I 



Co-Chairmen 

 A. V. Nebeker 

 D. H. Fickeisen 



Laboratory studies of the effects of dissolved gas 

 supersaturation on aquatic organisms have been 

 designed primarily to determine acute tolerance 

 using death as an endpoint. 



Gas supersaturation is an immediate and 

 urgent problem in the Columbia River system, 

 particularly with regard to salmonid resources, 

 requiring management decisions on a time scale 

 which precludes long-term or basic studies of the 

 effects of dissolved gas supersaturation on aquatic 

 biota. We have by necessity focused on short-term 

 experiments designed to answer questions of 

 lethal levels of gas saturation, in most cases during 

 acute experiments. These tests assume that once 

 exposed to excess dissolved gas an organism 

 becomes and remains supersaturated. However, 

 two other contingencies exist: the gas solubility 

 may be increased (i.e., by sounding to increase 

 hydrostatic pressure or by decreasing the tempera- 

 ture) or the tissue dissolved gas content may be 

 decreased (by re-equilibration with water having 

 a lower dissolved gas tension). If neither of these 

 occurs, the excess gas will leave solution and form 

 gas-phase bubbles causing gas bubble disease. 



Hydrostatic pressure increases gas phase 

 partial pressures such that the gas saturation level 

 of an organism decreases as it moves to a deeper 

 location. Most river systems subject to artificial 

 supersaturation are deep enough to permit this 

 pressure compensation, but the behavior of fishes 

 exposed to supersaturation is poorly understood. 

 Factors other than gas levels (e.g., light, tempera- 

 ture, prey density, pressure) may cause a depth- 

 selective response. Trauma due to gas bubble 

 disease may be another stimulus affecting depth 

 distribution. Diadromous species are forced to 

 surface when passing over dams, decompressing, 

 and perhaps producing gas bubble disease when 

 the hydrostatic pressure decreases. 



Dissolved gases move down a gradient of gas 

 tension: the external gas tensions must be less 

 than the internal tension at the exchange surface 

 for a net outward flux of gas to take place. 



There is some evidence that the rate of equili- 

 bration between organisms and water is rapid, with 



772 Round Table Discussion 



equilibration nearly complete in a matter of 1 to 2 

 hr. Re-equilibration is also rather rapid; however, 

 in the Columbia River system re-equilibration 

 during the spillway operating season is not feasible 

 under present operating schemes as essentially the 

 entire system is artificially supersaturated for ex- 

 tended periods. 



During acute tolerance tests we have recog- 

 nized that additional information on swimming 

 depth distribution, behavioral responses to gas 

 supersaturation, and effects of intermittent expo- 

 sure to excess dissolved gases is needed. Long- 

 term and basic studies dealing with sublethal and 

 chronic effects at the population and ecosystems 

 level rather than limited to the individual level 

 should also be undertaken. Specific research needs 

 identified during the discussion include: 



• Sublethal and chronic effects of exposure 

 to gas supersaturated water. Effects on fecundity, 

 predator-prey relationships, and sensory physiology 

 require further study. 



• Combined stressor effects. More informa- 

 tion is needed detailing effects of temperature, 

 fish disease, and operations of hydroelectric facili- 

 ties acting with gas supersaturation. It is quite 

 possible that these and other factors act syner- 

 gistically to increase the magnitude of their indivi- 

 dual effects. 



• Gas bubble formation trigger mechanisms. 

 Initial experiments and a review of available data 

 indicate that mechanisms triggering bubble forma- 

 tion are multiple and differ in acute and chronic 

 tests. Basic physiological research is required to 

 define trigger mechanisms, effects of internal body 

 pressures and nucleation sites, and factors resulting 

 in bubble size stabilization. Differences in indivi- 

 dual gases also require attention. 



• Detection of and response to gas super- 

 saturation. Evidence regarding the ability of fishes 

 to respond to supersaturation is conflicting. Some 



Nebeker: U.S. Environmental Protection Agency, Corvallis, 

 Oregon; and Fickeisen: Battelle-Northwest, Ecosystems De- 

 partment, Richland, Washington. 



