BACK PRESSURE 

 VALVE 



fcs 



AIR OXYGEN 



AIR OXYC 

 I I MIXIKC I I 



CENTRIFUGAL 

 PUMP 



EQUILIBRATION 

 TRAYS 



AIR EQUILIBRATION 



FIG. 1 Schematic drawing of system used to produce water 

 supersaturated with dissolved atmospheric gas in shallow 

 water tanks. 



forated ends alternated to produce a back and 

 forth flow of water from tray to tray. Water was 

 then collected in a plexiglass box (18 in. x 18 in. 

 x 10 in. deep) with a false bottom of porous poly- 

 ethylene plate through which air was passed. The 

 level of supersaturation desired for each test tank 

 was maintained by regulating the number of per- 

 forated trays and the amount of air supplied to 

 the collection boxes. Water from each box was 

 gravity fed to a test tank through a vinyl tube, end- 

 ing at the water surface. A flow rate of 7.5 xVmin 

 was maintained which created a circulation at 

 about 0.2 m/sec within the test tank. 



Test tanks were made of green tinted fiber- 

 glass, 1.2 m in diameter and of two heights, 0.6 m 

 and 3.0 m (shallow, deep), holding about 270 and 

 2700 C of water, respectively. A plexiglass window 

 extended from the top to the bottom of the 

 deep tanks allowing observations to be made over 

 the entire water column. Curtains covered the 

 windows and were removed only at times of obser- 

 vation. Water drained from the bottom of these 

 tanks through an external standpipe. 



Lighting was controlled with time clocks to 

 simulate natural sunrise and sunset and light inten- 

 sity at the surface of each test tank was from 10 

 to 20 lumens/ft 2 during full intensity periods. 



Water quality determinations for parameters 

 other than dissolved oxygen and nitrogen were 

 made before testing began and once each week or 

 once every 4 weeks depending on the parameter 

 measured (Table 2). Analysis procedures were 

 those of A.P.H.A., Standard Methods for the 

 Examination of Water and Waste Water, 1971. 

 The monthly measurements were made by per- 

 sonnel of the State of Washington Department of 

 Ecology using a P & E 303® atomic absorption spec- 

 trophotometer. All concentrations of heavy metals 

 or other potentially dangerous compounds fell 

 below potential danger levels to salmon and steel- 

 head (McKee and Wolf, 1969). 



Dissolved gas analyses were made on each tank 

 at least once each weekday for the first 2 weeks, 

 then a minimum of twice each week for the rest of 

 the test period. Procedures were identical to Dawley 

 and Ebel (1974). A gas chromatograph was calibrated 

 for nitrogen and argon using a modified manometric 

 blood gas analysis apparatus (Van Slyke and Neill, 

 1924). The modified Winkler procedure (A.P.H.A., 

 1971) was used for analysis of oxygen concentrations. 

 Water samples were collected by use of a siphon 

 tube from the middle of the water column in the 

 shallow tanks and from the surface of the deep tanks. 

 Gas concentrations remained steady throughout the 

 test periods and mean values for each tank did not 

 change more than 1% on a weekly basis with stan- 

 dard deviations for both tests less than 2.6% 

 T.D.G. overall (Table 3). Samples were taken from 

 the top, middle and bottom of the water column of 

 the deep tanks several times and gas concentrations 

 were found to be uniform throughout the tank. 



RESULTS 



Lethal Effects of Dissolved Gas 



Chinook groups held at 120% and 115% of 

 saturation in the shallow tanks and at 127% and 

 124% in the deep tanks sustained substantial mor- 

 tality (67%-97%) after 60 days of exposure. By the 

 same time, 13% mortality had occurred in groups 

 held at 110% in shallow tanks and 4% had occurred 

 in groups held at 120% in deep tanks. Mortality 

 was insignificant in groups held at lower gas con- 

 centrations. Curves of accumulative mortality for 

 all test groups are shown in Fig. 2. Average cumula- 

 tive mortality in the control tanks was minimal 

 (3%) for the first 60 days, but by day 127 had 

 sharply increased to 26.3% in the shallow tanks 

 and 13.6% in the deep tanks. 



A change in normal feeding response and swim- 

 ming behavior of chinook groups (both deep and 

 shallow) was noticed on day 64 of the test. We be- 

 lieve these changes resulted from an infection 

 caused by Cytophaga psychrophila. All groups (test 

 and control) were taken from test tanks and bathed 

 in a 10 ppm solution of terramycin for 1 hr. A supple- 

 ment to the daily ration of 0.5% oxytetracycline was 

 administered for the following 10 days, and after a 

 2-week interval another 0.5% supplement was added 

 for 10 days. After the second treatment (day 100) the 

 fish in all tanks behaved normally. 



Steelhead groups held at 120% and 115% of satu- 

 ration in shallow tanks developed substantial mor- 

 tality within 7 days, 100% and 57% respectively, 



•Trade names referred to in this publication are not an endorse- 

 ment of commercial products by the National Marine Fisheries 

 Service. 



Long-Term Exposure of Salmonids 3 



