DAWLEY and EBEL: EFFECTS OF DISSOLVED GASES ON SALMONIDS 



dead fishes). Signs that developed at low^er levels 

 (110-115%) were obviously different from those 

 appearing at the higher saturations; i.e., gas 

 blisters in and around the eye, exophthalmia, cu- 

 taneous gas blisters on the head and in the mouth, 

 and spinal flexures. Neither set of signs (low-level 

 or high-level types) correlate by percent of in- 

 cidence or severity, with accumulative mortality. 

 But they showed that one could determine with 

 reasonable accuracy, whether fish observed in the 

 river had been exposed to supersaturation for a 

 long or short duration. Populations with signs of 

 chronic exposure (exophthalmia, spinal flexures, 

 etc.) could have been either 1.5 to 2.0 m deep in 

 highly supersaturated water (130-135%) or near 

 the water surface at near 115% saturation. 



SUMMARY AND CONCLUSIONS 



Bioassays in shallow tanks (25 cm) with dis- 

 solved nitrogen and argon gas concentrations 

 ranging from 100 to 125% of saturation were con- 

 ducted to determine lethal and sublethal effects on 

 juvenile chinook salmon and steelhead trout. 



Juvenile steelhead (130 mm fork length) reached 

 the LE50 level within 35 days when exposed to 

 115% of nitrogen and argon saturation (112% 

 TDG), whereas mortality of juvenile chinook (115 

 mm) did not exceed 7%. There appeared to be 

 no substantial difference between susceptability 

 of chinook and steelhead at 120 or 125% saturation 

 N2 +Ar. No mortality related to supersaturation 

 occurred in either juvenile chinook or steelhead 

 trout exposed to 110 or 105% saturation Ng -^-Ar. 

 Signs of gas bubble disease (such as bubbles in 

 lateral line and exophthalmia) were evident on 

 both species, however, after 35 days exposure to 

 110%. 



Time to death decreased in test tanks with 

 higher oxygen concentrations (thus higher TDG) 

 even though nitrogen and argon concentrations 

 were identical, indicating that oxygen as well as 

 nitrogen and argon concentrations must be con- 

 sidered when time to death values are compared. 



The first notable sign of gas bubble disease was 

 appearance of bubbles in the lateral line which 

 appeared in some degree at all gas concentrations 

 tested. Exophthalmia, dermal gas blisters of the 

 buccal cavity and cephalic regions, and spinal 

 flexures did not occur with short-term exposure (6 

 days) or at the higher levels (120 and 125%) but was 

 prevalent after long exposure at both 115 and 110% 

 saturation Ng + Ar. External gas bubble disease 



signs disappeared within 15 days when fish were 

 placed in normally saturated water (100%). 



Fish stressed with supersaturation at sublethal 

 levels for 35 days grew less than controls and the 

 swimming performance of juvenile chinook ex- 

 posed for sublethal periods to 110-125% nitrogen 

 saturation was significantly lower than controls. 

 Blood chemistry measurements indicated that 

 significant differences occurred between blood 

 samples taken from test and control chinook and 

 steelhead after they were exposed to levels of 115% 

 saturation. Serum calcium, for example, was 10- 

 17% lower in samples taken from test groups of 

 steelhead. 



We concluded from these experiments that: 



1. Significant mortality of both juvenile chinook 

 and steelhead trout commences at about 115% sa- 

 turation of nitrogen and argon (111% TDG). 



2. Sublethal exposures to various concentra- 

 tions of dissolved gas significantly affects swim- 

 ming performance, growth and blood chemistry of 

 chinook, and growth and blood chemistry of 

 steelhead trout. 



3. The first externally evident sign of gas bub- 

 ble disease on juvenile chinook and steelhead trout 

 exposed to supersaturation occurs as bubbles in 

 pores of the lateral line. 



4. Fish returned to normally (100%) saturated 

 water appear to recover within 15 days from ex- 

 posure to supersaturated water. 



LITERATURE CITED 



American Public Health Association, American Water Works 

 Association, and Water Pollution Control Federation. 

 1971. Standard methods for the examination of water and 

 wastewater. 13th edition. Am. Public Health Assoc, 

 Wash., D.C., 874 p. 

 Beiningen, K. T., and W. J. Ebel. 



1971. Dissolved nitrogen, dissolved oxygen, and related 

 water temperatures in the Columbia and lower Snake 

 rivers, 1965-69. U.S. Dep. Commer., NOAA, Natl. Mar. 

 Fish. Serv., Data Rep. 56, 60 p. on 2 microfiche. 

 Doudoroff, R. 



1956. Water quality requirements of fishes and effects of 

 toxic substances. In M. E. Brown (editor), The 

 physiology of fishes 2:403-430. Academic Press Inc., N.Y. 

 Ebel, W. J. 



1969. Supersaturation of nitrogen in the Columbia River 

 and its effect on salmon and steelhead trout. U.S. Fish 

 Wildl. Serv., Fish. Bull. 68:1-11. 

 1971. Dissolved nitrogen concentrations in the Columbia 

 and Snake Rivers in 1970 and their effect on chinook 

 salmon and steelhead trout. U.S. Dep. Commer., NOAA 

 Tech. Rep. NMFS SSRF-646, 7 p. 

 Ebel, W. J., E. M. Dawley, and B. H. Monk. 



1971. Thermal tolerance of juvenile Pacific salmon and 



795 



