TABLE 7 Crayfish Mortality After 30 Days at 150%, 140%, 130%, 



120%, and 100% Total Gas Saturation at 12°C, and Observed 



Signs of Gas Bubble Disease 1 (Test 6) 



100% 



Size similar to others (all unaffected after 

 30 days) 



'WFTS Test No. 30. 



The first death occurred after 49 hr of exposure 

 at 150%, and many bubbles were observed in the 

 body fluids. Fifty percent were dead at 150% after 

 123 hr (Table 2), and all had bubbles in the body 

 fluids (Table 8). There was no difference in the sus- 

 ceptibility of males and females and all were dead 

 after 262 hr of exposure. Fifty percent had died at 

 140% after 165 hr and all had bubbles in the tissues 

 and body fluids. All had died after 329 hr (2 weeks) 

 when the test was terminated. Crayfish exposed to 

 130% were accidentally killed and no data were 



300 400 



TIME (H0URSI 



FIG. 11 Time to death for the crayfish Pacifastacus leniuscutus 

 exposed to 120%, 130%, 140%, and 150% total dissolved gas 

 (Test 6). 



obtained. No deaths occurred at 120%, and no 

 apparent signs of GBD were observed during the 

 2-week exposure period. 



A lethal threshold concentration for crayfish in 

 supersaturated water was determined by using time 

 to 20% death as the criterion (Fig. 12). The thresh- 

 old concentration where crayfish were apparently 

 safe, at least for 30 days, was near 127% total dis- 

 solved gas. 



END OF TEST 



110 120 130 140 



PERCENT SUPERSATU RATION 



FIG. 12 Threshold concentration determined for the crayfish 



Pacifastacus leniusculus. 



Insect Tests 



Test 8 



The stonefly species Pteronarcys californica 

 and Acroneuria pacifica were tested at 125% total 

 dissolved gas saturation for 12 days at 12°C to 

 determine their comparative sensitivity with cray- 

 fish and young steelhead trout. Ten stoneflies, five 



Effects on Freshwater Invertebrates 67 



