FIG. 9 Dorsal view of crayfish. Left: with bubbles under the 

 distended membrane between the carapace and the abdominal 

 segments. Right: control. 



FIC. 10 Crayfish gills showing bubbles inside the gill mid-rib 

 and filaments. 



Crayfish No. 6 was alive after 47 hr, but was 

 unable to control chelapods or to pinch. Crayfish 

 No. 7 was alive and, with difficulty, was able to 

 manipulate chelapods. Crayfish No. 8, 9, and 10 

 were alive and able to swim with good coordination. 

 Another large male, necropsied after 64 hr, was 

 turgid and swollen from internal pressures of gas 

 and from water taken up because of osmotic 

 imbalance (generalized stress reaction in inverte- 

 brates). Many bubbles were present in the body 

 fluid, gills, and associated structures; bubbles could 

 also be seen through the abdominal sternites. One 

 crayfish died after 88 hr; three remained alive. Bub- 

 bles were conspicuous in the body fluid of the dead 

 crayfish and could be seen through the body wall. 



They could be observed through the thin portions 

 of the exoskeleton, legs, ventral abdominal ster- 

 nites, and membranous joints. The last three cray- 

 fish were dead after 6 days. 



Water supersaturated at 150% total dissolved 

 gas, acutely lethal to trout in less than an hour 

 (Nebeker, unpublished data), was acutely debilitat- 

 ing to crayfish, though not immediately lethal, as 

 they remained in an advanced state of immobility 

 with no coordinated movements for several days 

 after a possible "ecological death point" was 

 reached. 



Test 6 Crayfish were tested at 150%, 140%, 130%, 

 120%, and 100% total dissolved gas saturation at 

 12°C for 30 days (Table 7). Ten crayfish were 

 exposed to each gas level, five each in two of the 

 four net cages in each tank. An additional 10 cray- 

 fish were placed in the open tank at 150% saturation. 

 Two stainless steel wire cages were also suspended 

 in the test water in each tank, and one crayfish was 

 placed in each cage. 



Thirty percent were dead after 40 hr (Fig. 11) 

 at 150%, and many bubbles were readily apparent 

 in the body fluid, gills and other tissues. There was 

 no correlation between crayfish size and time to 

 death in any of the tests. All were dead after 96 hr 

 at 150%. Fifty percent were dead after 330 hr 

 (Table 2) at 140%, and most exhibited some degree 

 of bubbles in body fluids and tissues (Fig. 9 and 

 10). There was an obvious difference in feeding 

 behavior between crayfish at 140% and controls 

 (100%) after 96 hr. Crayfish at 140% moved slowly 

 or hardly at all, whereas the controls jumped and 

 swam when startled and moved about freely when 

 disturbed. All crayfish tested at 140% were dead 

 after 595 hr (24 days). 



Two crayfish died at 130%, one after 215 hr and 

 one after 453 hr (Table 7); both had bubbles in their 

 body fluid. No crayfish died at 120% during the 

 30-day test, and no changes were apparent in feed- 

 ing behavior when compared to control animals. 

 Water supersaturated at 120% was apparently safe 

 for crayfish over a 30-day period. 



Bubbles were abundant in the small branchiob- 

 dellid worms living on the carapace of the test cray- 

 fish from 140%, but were not present in those from 

 control water. The five young sockeye salmon 

 placed in 140% were immediately affected; one had 

 died, one had lost equilibrium, and one had hemor- 

 rhage popeye after 4 hr of exposure. 



Test 7 Crayfish were tested at 150%, 140%, 130%, 

 120%, and 100% total dissolved gas saturation at 

 12°C for 2 weeks. Males and females were tested 

 separately with five males in one net cage and five 

 females in another, giving a total of 10 crayfish 

 per gas level. 



60 Nebeker, Stevens, Brett 



