terminated 80% were dead after 96 hr (Table 3), and 

 50% had observable bubbles in the gut or brood 

 pouch (Fig. 5). Time to 50% death at 130% was 65 hr, 

 and 80% were dead after 96 hr. Ten percent at 140% 

 and 130% were carrying eggs. The time at which 

 50% died at 120% saturation was 91 hr. Sixty per- 

 cent were dead after 96 hr at 120% and all were 

 carrying young, indicating much better reproduction 

 at the lower gas level (Fig. 6). 



Test 2 Young non-egg-carrying adults were tested 

 at 150%, 140%, 130%, 120%, and 100% total dissolved 

 gas at 12°C for 11 days and were held in the 7.5 by 

 12.5 cm screen cages sheltered from direct current 

 by a larger screen cage (Fig. 6). Ten Daphnia were 

 placed in each cage, and two cages were immersed 

 in each of the five exposure tanks. 



At 150% all were alive after 24 hr but many 

 had air in the gut and brood pouch and were swim- 

 ming at the surface. The first deaths occurred at 

 52 to 53 hr at 150% and 140%, indicating a delayed 

 lethal effect not directly attributable to blockage of 

 vital fluids, as in fish (Table 4). Mean time for 50% 

 death at 150% was 101 hr. Mean time to 50% death 

 was 123 hr at 140% saturation, and all had died at 

 198 hr. Fifty percent were dead after 130 hr at 130%, 

 and many had air in the gut and were held at the 

 water surface (Table 4). Mean time to 50% death at 

 120% was 210 hr (Table 3), and 70% were dead when 

 the test was terminated after 264 hr (Fig. 7). 



Test 3 Daphnia were tested at 120%, 115%, 110%, 

 and 100% saturation at 12°C for 1 week. Two 7.5 

 by 12.5 cm screen cages with petri dish bottoms 



TABLE 3 Daphnia Mortality After % hr at 140%, 130%, 120%, and 100% Total Gas 

 Saturation at 12 0, and Observed Signs of Gas Bubble Disease 1 (Test 1). 



Percentage 

 saturation 



Daphnia 



No. 



Time to 

 death (hr) 



Signs of gas bubble disease (GBD) 

 (B = Bubbles) 



140% 1 40 One B inside carapace - body fungused 



2 40 No B - lying on cage bottom 



3 64 B in brood pouch - fungused 



4 64 B in gut and carapace 



5 64 3-4 B under carapace 



6 70 No bubbles 



7 70 One B under carapace 



8 88 Body badly fungused 



9 96* No heart beat - no B, slight movement, half out of molt 



10 96** Food in fore- and midgut, B filling hindgut, B in brood pouch crowding 3 young 



130% 



1 



2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 



40 No internal B, 3-4 clinging externally 



40 One B inside carapace - body badly fungused 



40 One B inside carapace - fungused 



64 Fungused 



64 Fungused 



64 Fungused 



70 No bubbles or fungus 



88 Gut full of air - fungused 



96* Gut full of air, no heart beat, slight movement of appendages 



96** Gut full of air, heart beating well, carrying ephyppia (2 eggs) 



120% 



1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 



40 No bubbles apparent 



40 4 small B clinging externally 



64 Many B - in gut, brood pouch and under carapace 



88 2 B under carapace, some fungus 



88 No B - carrying 2 small eggs 



91 Gut full of air 



96** No B, carrying embryos 



96** Gut full of air, B in brood pouch with 2 young 



96** Gut 4/5 full of air, carrying several young 



96** Gut 1/2 full of air, carrying several young 



100% 

 (Control) 



1-10 



'WFTSTest No. 31. 

 •Barely Alive - 96 hr 

 **Alive and Active - 96 hr 



Controls 2 dead, but with live young, no bubbles 



Effects on Freshwater Invertebrates 55 



