Protection by two complexing agents, thiosulphate and dissolved organic matter, against the physiological effects of silver nitrate to rainbow trout ( Oncorhynchus mykiss) in ion-poor water

Adult rainbow trout ( Oncorhynchus mykiss) were exposed in ion-poor water (∼50 μM Ca) to silver added as AgNO 3 or to AgNO 3 plus either thiosulphate (Na 2S 2O 3) or dissolved organic matter (DOM). The effects of these exposures were assessed through repetitive blood sampling over 4 days. Trout exposed to 0.1 μM AgNO 3 alone accumulated large amounts of Ag on their gills and in their plasma, showed progressive losses of plasma Na and Cl, and had elevated concentrations of plasma glucose. In one set of exposures trout exposed to AgNO 3 alone also had increased cough rates, slightly higher ventilation rates, somewhat lower arterial oxygen tensions, and increased blood lactate concentrations. In contrast, trout exposed to 0.1 μM AgNO 3 plus 5 μM thiosulphate or 35 mg C l −1 DOM accumulated less Ag on their gills and in their plasma, and showed no adverse ionoregulatory or respiratory effects due to Ag. These results demonstrate ionoregulatory and sometimes respiratory effects in fish exposed to ionic Ag + in ion-poor water, depending on water chemistry, and demonstrate the protective effects of synthetic and natural complexing agents through a reduction in the amount of ionic Ag + available to bind at the gills.