valves of oysters, and bubbles were observed in 

 gill filaments. The cause, increased water tempera- 

 ture with subsequent supersaturation of dissolved 

 gas, is a common occurrence and surely is respon- 

 sible for much more damage to aquatic animals 

 than is documented in the literature. Gas bubble 

 disease in larval and juvenile brown shrimp 

 (Penaeus aztecus) was recently described by 

 Lightner et al. (1974). Stage II protozoeal, larval 

 shrimp developed the disease after being placed 

 in water warmed in a closed heater that did not 

 allow excess gas to escape. Ten percent of the 

 shrimp were affected (5% died) and had gas bub- 

 bles under the carapace and either in the gut or 

 the hemocael surrounding the gut. No saturation 

 levels were given. Most freshwater invertebrates 

 are probably less sensitive to GBD than fish, 

 although there are exceptions, like Daphnia. In 

 general, if fish are protected by reasonable water 

 quality standards, the invertebrates will probably 

 be protected also. However, further work should be 

 done with important freshwater and marine inverte- 

 brate species to determine their comparative toler- 

 ance and to define their most sensitive life stages. 



relatively simple compared to fish, appeared to be 

 the main reason for the greater tolerance of insects 

 and Crustacea to gas bubble disease. They do not 

 have the complex capillary-blood-vessel system of 

 fish, which is rapidly blocked by the bubbles or 

 emboli that form in the blood. 



The tough exoskeleton of insects and Crustacea 

 prevents much of the surface injury and secondary 

 infections that are common to fish exposed to 

 supersaturated water. 



ACKNOWLEDGMENTS 



We wish to thank Mike McCarthy, Jim Fendrick, 

 and Lynn Jones, Oregon State university student 

 aids, for help with the numerous gas and water- 

 chemistry analyses; Robert Rulifson for the initial 

 saturometer and aid during construction and use of 

 the present models; and Earl Dawley and Larry 

 Davis for assistance with saturometer calibration. 

 We also thank Dee Boczkiewicz, Don Samuelson, 

 Gerald Bouck, Gary Chapman, and Ronald Garton 

 for assistance and Robert Trippel for help with 

 construction and operation of test equipment. 



CONCLUSIONS 



Daphnia magna was affected by gas-saturated 

 water >115%. Signs of gas bubble disease ranged 

 from no obvious effects to massive air bubbles in 

 the gut, brood pouch, and under the carapace. Bub- 

 bles were rarely observed in the body fluid. Death 

 in most cases was due to physical blockage of the 

 gut by air emboli, with subsequent starvation. The 

 most obvious sign of gas bubble disease was the 

 buoyancy created by bubbles, which caused the 

 Daphnia to float at the water surface. The heart 

 was apparently unaffected. 



Crayfish were tolerant of supersaturated water 

 and were alive with no apparent effects at 120% 

 and 125%, levels that were lethal to the young 

 steelhead trout tested with them. Bubbles were 

 found in body fluids, gills and other tissues of cray- 

 fish that died at 140% and 150% total gas pressure. 

 They were more resistant to supersaturated water 

 than any of the 12 fish species tested at the Western 

 Fish Toxicology Station (Nebeker, unpublished 

 data). 



Aquatic insects, represented by the three stone- 

 fly species, were also comparatively tolerant of gas- 

 supersaturated water. No deaths occurred at 125%, 

 but some insects were immobilized and had air bub- 

 bles in the body fluids. They recovered rapidly 

 (4 hr) when transferred from supersaturated to 

 saturated water. Increased buoyancy was observed 

 and could increase mortality of insects from 

 predation. 



The open circulatory system of invertebrates. 



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64 Nebeker, Stevens, Brett 



