Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8972
Title: Studies on effects of supersaturation of dissolved gases on fish
Author/Editor: Earl M. Dawley, Theodore H. Blahm, George R. Snyder, Wesley J. Ebel
Publication Year: 1975
Publisher: National Marine Fisheries Service
Contracting Agency: Bonneville Power Administration, U.S. Bureau of Reclamation, and U.S. Army Corps of Engineers. Portland, Oregon

Nitrogen supersaturation studies were conducted by staff of the National Marine Fisheries Service during the 3-year period 1972-1975.  Research was selected from priorities established by a sub-committee representing water use and pollution control agencies.  We report results from the following five areas of study

  1. Detection and avoidance, both lateral and vertical
  2. Intermittent exposure, tested in both laboratory and field experiments
  3. Bioassays and predation survival
  4. Physiological effects including stamina, O2 consumption, blood chemistry, and lateral line function
  5. Effects of O2/N2 ratio

Lateral movement as an indication of an avoidance response to supersaturated water was investigated with two species of salmon: steelhead Oncorhynchus mykiss and Chinook salmon O. tshawytscha.  Test fish were given a choice of inhabiting high or normally saturated water.  One-half of a shallow trough area was supersaturated and one-half was not; free access was allowed to both areas.  Tests indicated that Chinook salmon may be able to avoid areas with high N2 levels, while steelhead may not.

Vertical movement as an indicator of an avoidance response to supersaturation was also investigated with steelhead and Chinook salmon.  Vertical positioning of the fish was observed hourly under varied conditions of turbidity, light, and restricted vs. unrestricted depth.

Observations made from these and other studies indicate that both chinook and steelhead juveniles usually displayed an avoidance to supersaturation by sounding.  However, the avoidance behavior was not sufficient to prevent mortality.  Avoidance behavior changed when turbidity was introduced; i.e., fish remained in shallower water.  Depth distribution also changed from night to day, even when test tanks were lighted day and night.