Observations on gas bubble disease among adult smallmouth bass and squawfish in the lower Snake and mid-Columbia Rivers

Abstract

In 1976 and 1976, 179 smallmouth bass (Micropterus dolomieui) and 85 northern squawfish (Ptychocheilus oregonensis) were collected by angling from the lower Snake and mid-Columbia Rivers, southeastern Washington. All fish were examined externally for gas bubble syndrome. Emboli were found beneath membranes of the operculae, body and fins of 128 bass (72%) and 71 squawfish (84%). Hemorrhage was also noted on the caudal, anal and pectoral fins of several bass. Presence of gas bubble syndrome corresponded to the spring runoff when total dissolved gas supersaturations in river water exceeded 115%. Effectiveness of measures to reduce supersaturation levels for protection of salmonid outmigrants could be reflected in resident river fish. Hydroelectric dams on the Columbia and Snake rivers have created a source of environmental stress, causing bubble ``disease`` among fish populations (Collins et al. 1975, Ebel 1977). Water passing over spillways during the spring runoff entrains air, imparting excessively high levels of dissolved gases to the river below. Distances between successive dams, which are linked together by reservoirs, are usually too short for river water to equilibrate to normal saturation levels. Therefore, high saturations of gases are maintained as the water reaches each successive downstream structure.