Subchronic Toxicity of Low Dissolved Oxygen Concentrations, Elevated pH, and Elevated Ammonia Concentrations to Lost River Suckers

Abstract

Abstract The Lost River sucker Deltistes luxatus is a federally listed endangered fish species that inhabits hypereutrophic Upper Klamath Lake in southern Oregon. We conducted four subchronic toxicity tests with Lost River suckers by continuously exposing them to low dissolved oxygen (DO) concentrations for 14 d (late juveniles); elevated pH for 30 d (late larvae); elevated ammonia concentrations for 30 d (late larvae); and sublethal ammonia concentrations for 14 d followed by sublethal low DO concentrations for 14 d (early juveniles). Mortality thresholds were approximately 1.4 mg/L in the DO test, more than 10.0 in the pH test (the highest pH tested), and between 0.37 and 0.69 mg NH3-N/L in the ammonia test. Contrary to the common expectation for fish exposed to toxicants, Lost River suckers generally did not display sublethal responses (i.e., reduced growth, altered whole-body ion content, and reduced swimming performance) to low DO concentrations, elevated pH, or elevated ammonia concentrations. In th...