Gas bubble reabsorption in Chinook salmon: Pressurization effects

Publication Date



adult, bubbles, bypass, bypass systems, chinook, Columbia River, fish ladder, fish passage, gas bubble disease, history, monitoring, mortality, Oncorhynchus tshawytscha, salmon, salmonids, smelt, Snake River, spillway, turbines, upstream

Journal or Book Title

Journal of Aquatic Animal Health


Gas bubble disease (GBD) can cause substantial morbidity and mortality of salmonids and other fishes residing in gas supersaturated water. The monitoring program for examining the prevalence of GBD in the Columbia and Snake rivers is only based on fish collected in the smelt bypass systems; fish that pass through the turbines, nagivation locks, adult fish ladders, or spillways are not sampled. The current monitoring program may underestimate the prevalence and severity of GBD because the high hydrostatic pressures experienced by the smelts as they pass through the smelt bypass system may cause rapid reabsorption of any gas bubbles that had formed upstream of the dam. A pressurization of 5 min to 30.5 m of head resulted in a substantial reduction in clinical signs of GBD in the fins, lateral lines, and gills of yearling spring chinook salmon Oncorhynchus tshawytscha. Clinical signs of GBD were lost most rapidly in gills, followed by the lateral line. The rate of bubble loss was much less for the primarily extravascular bubbles found in the fins. The gas transfer potential of pressure and length of exposure to pressure (pressure-time history) must be considered for smelts exposed to the bypass system. If the gas transfer poten tial of pressure-time history for in-river salmonids is similar to the 5-min pressurization treatment, the current smelt monitoring program aimed at evaluating the prevalence and severity of GBD, may be under-estimating the impact of GBD in the Snake and Columbia rivers. This work demonstrates that gas bubble reabsorption could be occurring in salmonid smelts examined at fish passage facilities and that further work is needed to quantify the extent and magnitude of bubble reabsorption at such facilities







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