Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7755
Title: Effects of supersaturated dissolved atmospheric gases on northern squawfish, Ptychocheilus oregonensis
Author: Wallace W. Bentley, Earl M. Dawley
Publication Year: 1981
Journal: Northwest Science
Volume: 55
Issue: 1
Pages: 50-61

Northern squawfish, Ptychocheilus oregonensis, were confined in shallow tanks for 12 d to study their tolerance to various concentrations of total dissolved atmospheric gases (TDG).  The TOG concentrations ranged from 100 to 126 percent of saturation&nmdash;levels that occur in the Columbia and Snake Rivers downstream from dams during periods of high flow.  Mortality did not occur in tests at or below 110 percent of saturation, but 32 percent of the fish succumbed in 12 d at 117 percent of saturation and 100 percent died in 20 hours at 126 percent of saturation.  Average daily food consumption of squawfish decreased in proportion to increased saturation levels.  At 100 percent of saturation ( normal gas content), 14.2 g of food per fish per day were consumed; at 117 percent, 6.2 g; and at 120 percent, only 2.3 g per fish per day were consumed.

Field studies (1974 to 1976) indicated squawfish in the Snake River may not be seriously affected by supersaturation (from 117 to 141.5 percent of saturation).  Gill-net drifts in the tailrace of dams showed that most squawfish were below the 3-m depth; therefore, they were at equilibrium and were unaffected by nitrogen supersaturation in the river.  High TDG levels did not appear to hinder movement within 92 km of the study area.  Purse-seining adjacent to dams during spill closures indicated squawfish were actively feeding on fingerling salmon but probably did so from an equilibrated depth.