The effect of dissolved oxygen and salinity on the toxicity of ammonia to smolts of salmon, Salmo salar L.

The survival of Atlantic salmon smolts on exposure to constant concentrations of ammonia has been measured under laboratory conditions. At concentrations of dissolved oxygen close to the air-saturation value, the 24-h LC50 of un-ionised ammonia is 0.15 mg NH₃1^?1 in fresh water (hardness 264 mg 1^?1 as CaCO₃) and 0.3 mg NH₃1^?1 in 30% sea water; at concentrations of dissolved oxygen of 3.5 mg 1^?1 in fresh water and 3.1 mg 1^?1 in 30% sea water, the 24-h LC50 is 0.09 mg NH₃ 1^?1 and 0.12 mg NH₃ 1^?1 respectively; for fish acclimated for 1 day to a concentration of ammonia close to the 24-h median for un-acclimated fish, the median is increased between 38 and 79%, depending on test conditions.