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Abstract-While there is considerable information on freshwater toxicity of Ag to fish, little is known about the toxicity of Ag in marine systems. In the present study, standard 96-h acute toxicity tests were performed on seawater-acclimated rainbow trout in water at 25‰ salinity. Toxicity tests were repeated in various salinities (15, 20, 25, and 30‰) at the 50% lethal concentration (LC50) for Ag in 25‰ to investigate the influence of salinity on toxicity. Computer speciation modeling by MINEQL ϩ was performed in order to gain insight into the variation of Ag species over a range of salinities from freshwater to oceanic seawater at S 2Ϫ -free conditions. At 25‰ salinity the LC50 was determined to be 3.75 M (401 g/L) Ag. No mortality was observed at this Ag concentration in 15 or 20‰ salinities. Mortality increased to 50% in 25‰ seawater and again to 67% at 30‰. Based on the results of speciation modeling, an increase in a more toxic AgCl n species is unlikely. The increased toxicity with salinity may instead be linked to an incomplete hypoosmoregulatory ability of the rainbow trout.

While there is considerable information on freshwater toxicity of Ag to fish, little is known about the toxicity of Ag in marine systems. In the present study, standard 96-h acute toxicity tests were performed on seawater-acclimated rainbow trout in water at 25‰ salinity. Toxicity tests were repeated in various salinities (15, 20, 25, and 30‰) at the 50% lethal concentration (LC50) for Ag in 25‰ to investigate the influence of salinity on toxicity. Computer speciation modeling by MINEQL ϩ was performed in order to gain insight into the variation of Ag species over a range of salinities from freshwater to oceanic seawater at S 2Ϫ -free conditions. At 25‰ salinity the LC50 was determined to be 3.75 M (401 g/L) Ag. No mortality was observed at this Ag concentration in 15 or 20‰ salinities. Mortality increased to 50% in 25‰ seawater and again to 67% at 30‰. Based on the results of speciation modeling, an increase in a more toxic AgCl n species is unlikely. The increased toxicity with salinity may instead be linked to an incomplete hypoosmoregulatory ability of the rainbow trout.