NOTES 



GAS-BUBBLE DISEASE: MORTALITIES OF 



COHO SALMON, ONCORHYNCHUS KJSUTCH. 



IN WATER WITH 



CONSTANT TOTAL GAS PRESSURE AND 

 DIFFERENT OXYGEN-NITROGEN RATIOS' 



A review of the literature regarding gas-bubble 

 disease can be found in a recent publication by 

 Rucker (1972); one by the National Academy of 

 Science (Anonymous in press); and an unpublished 

 report by Weitkamp and Katz (1973).- Most dis- 

 cussions on gas-bubble disease have dealt with 

 the inert gas, nitrogen-oxygen was given a 

 secondary role. It is important to know the rela- 

 tionship of nitrogen and oxygen when we are 

 concerned with the total gas pressure in water. 

 Where water becomes aerated at dams or falls, 

 oxygen and nitrogen are usually about equally sat- 

 urated, however, many of the samples analyzed 

 from the Columbia River indicate that nitrogen is 

 often about 79f higher than oxygen when 

 expressed as a percentage. When oxygen is 

 removed from water by metabolic and chemical 

 action, or when oxygen is added to the water by 

 photosynthesis, there is a definite change in the 

 ratio of oxygen and the inert gases (mainly ni- 

 trogen with some argon, etc.). This present study 

 shows the effect of varying the oxygen and ni- 

 trogen ratio in water on fingerling coho salmon, 

 Oncorhiinchus. kisutch, while maintaining a con- 

 stant total gas pressure. 



The primary purpose of these experiments was 

 to determine differences in lethality of various 

 gas ratios of oxygen and nitrogen at a constant 

 total gas pressure of 119%. I also wished to deter- 

 mine whether there was a difference in suscep- 

 tibility between sizes and stocks of juvenile coho. 

 Also to be examined was the effect of reducing the 

 oxygen while holding the nitrogen constant. 



Methods 



Juvenile coho salmon averaging 6 cm in length, 

 obtained from the Quilcene National Fish 



Hatchery, Quilcene, Wash., and the Northwest 

 Fisheries Center of the National Marine Fisheries 

 Service, NOAA (National Oceanic and Atmo- 

 spheric Administration), Seattle, Wash., were 

 used during all the tests concerning differences in 

 lethality of O2 /N2ratios. During these tests water 

 temperatures were 13.6°+ 0.1°C. Gas concentra- 

 tions usually varied slightly from the desired 

 ratios. The tank facility consisted of six troughs, 

 two of which were used to hold experimental fish 

 at normal saturation (100%) and two pairs of 

 troughs used to test fish at different gas ratios. 



Control of gas concentrations and the test ap- 

 paratus is described in a subsequent section. Dur- 

 ing initial testing of the gas control system, I de- 

 termined that a ratio of 114% O2 to 121% N2 could 

 be achieved by merely allowing air to be sucked 

 into the intake side of the recirculation pump. 

 Since this gas ratio did not require injection of 

 either oxygen or nitrogen, the resultant concen- 

 tration (114% 02and 121% N2) was used as a quasi 

 control for comparison with the other gas ratios. 

 Several replicates were completed at this concen- 

 tration. Water saturated at this ratio and concen- 

 tration was also used to test for differences in size 

 and stock and to provide base line data in deter- 

 mining effect of reduced oxygen concentrations 

 while maintaining a constant nitrogen level. 



In all the tests free carbon dioxide was near 

 normal, or about 2 ppm. Oxygen is expressed as 

 "O2" and the inert gases as "Ng." 



The number of days required to kill 25% of the 

 fish at the different gas levels is expressed as the 

 lethal exposure-LEgsand to kill 50%- LE50. 



Apparatus shown in Figure 1 was used to supply 

 water with a definite oxygen and nitrogen con- 

 tent. The tank (1) was divided so that two 

 experiments could be carried on simultaneously 

 with similar equipment. Water was circulated by a 

 centrifugal pump (2) with a valve (3) on the 

 effluent side to cause a controlled back pressure as 

 read on a gauge (4). This created a vacuum on the 

 inflow side (5) so that air could be introduced into 

 the water with either oxygen or nitrogen (6) 



'Research performed under contract with the U.S. Army Corps 

 of Engineers. 



-D. E. Weitkamp and M. Katz. 1973. Resource and literature 

 review of dissolved gas supersaturation in relation to the 



Columbia and Snake River fishery resources. Submitted to 

 Northwest Utilities Cooperative, c/o Idaho Power Co., Boise, 

 Idaho, Apr. 3, 197.3, by Seattle Marine Laboratories, Div. of Xelco 

 Corp., Seattle, Wash., 55 p. (Typewritten.) 



915 



