Abstract
Duplicate groups of fingerling coho salmon (Oncorhynchus kisutch) were exposed to nine concentrations of un-ionized ammonia for 96 h. The LC50 was 0.45 mg un-ionized NH3N per liter (95% confidence limits, 0.43 to 0.47). Acute lethality ceased relatively early, presumably from an acceleration of biosynthetic detoxifying reactions, as shown by blood urea nitrogen measurements.