|R. R. Rucker 



Gas Bubble 

 Disease of 



Salmonids: Variation in Oxygen- 

 Nitrogen Ratio with Constant Total 

 Gas Pressure 



ABSTRACT 



Coho salmon fingerlings were subjected to a total gas pressure of 

 119% at 13.6°C with the O1/N2 varying from 50%/138% to 229%/ 

 90%. The small fish (3.8 to 6 cm) were the most resistant and the 

 larger fish (8 to 10 cm) the least resistant to gas bubble disease 

 at the gas concentrations used. A drastic decrease in lethal effect 

 of individual ratios of O2 to N> occurred between 159% O 2 /109% 

 N 2 and 173% O 2 /105% N 2 at the same total gas pressure (119%). 



A review of the literature regarding gas bubble dis- 

 ease can be found in a recent publication by Rucker 

 (1972); one in press by the National Academy of 

 Science (1972); and an unpublished report by Weit- 

 kamp and Katz (1973). Most discussions on gas bub- 

 ble disease have dealt with the inert gas, nitrogen; 

 oxygen was given a secondary role. It is important 

 to know the relationship of nitrogen and oxygen 

 when we are concerned with the total gas pressure 

 in water. Where water becomes aerated at darns or 

 falls, both oxygen and nitrogen are about equally 

 saturated 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 

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

 shows the effect of varying the oxygen and nitro- 

 gen ratio in water on fingerling coho salmon 

 (Oncorhynchus kisutch) while maintaining a 

 constant total gas pressure. 



GENERAL EXPERIMENTAL OBJECTIVES 

 AND METHODS 



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 suscepti- 

 bility between sizes and stocks of juvenile coho. 



Also to be examined was the effect of reducing the 

 oxygen while holding the nitrogen constant. 



Juvenile coho salmon averaging 6 cm in length, 

 obtained from the Quilcene National Fish Hatchery, 

 Quilcene, Washington, and the Montlake Labo- 

 ratory of the National Marine Fisheries Service, 

 Seattle, Washington, were used during all the tests 

 concerning differences in lethality of 2 /N 2 ratios. 

 During these tests temperatures were 13.6°C ^ 

 0.1°C. Gas concentrations usually varied very 

 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 differ- 

 ent gas ratios. 



Control of gas concentrations and the test 

 apparatus is described in a subsequent section. Dur- 

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

 mined 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 concentration (114% O2 

 and 121% N 2 ) was used as a quasi control for com- 

 parison with the other gas ratios. Several replicates 

 were completed at this concentration. This ratio 

 and concentration were also used to test for differ- 

 ences in size and stock and to provide base line 

 data in determining effect of reduced oxygen con- 

 centration while maintaining a constant nitrogen 

 level. 



In all the tests free carbon dioxide was found 

 near normal, about 2 ppm. Oxygen is expressed as 

 "0 2 " and the inert gases as "N 2 ". 



Rucker: Coastal Zone and Estuarine Studies Division, National 

 Marine Fisheries Service, Seattle. Washington. 



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