A nose-to-nose comparison of the physiological effects of exposure to ionic silver versus silver chloride in the European eel (Anguilla anguilla) and the rainbow trout (Oncorhynchus mykiss).

Physiological mechanisms of silver toxicity (as silver nitrate) to the sensitive rainbow trout (Oncorhynchus mykiss) (96 h LC50: 10.2 µg silver l(-1), in soft, low chloride water) and the more tolerant European eel (Anguilla anguilla)(96 h LC50: 34.4 µg silver l(-1), in the same water) were investigated during acute exposure to silver, using concentrations varying from 3 to 22 µg silver l(-1). Silver was present either predominantly in the form of ionic silver, or in the form of silver chloride complexes (AgCl(aq)). Inhibition of the branchial Na(+),K(+)-ATPase enzyme activity and the active influx of Na(+) leading to net Na(+) loss were the key toxic effect in both species. In the rainbow trout, but not in the European eel, Cl(-) influx was also impaired during silver exposure. However, even under control conditions, Cl(-) influx was negligible in the eel. Water Cl(-) clearly protected against the silver-induced physiological disturbance in rainbow trout, presumably by changing the speciation of silver from ionic silver to AgCl complexes. However, such a protective effect was not observed in the European eel. Differences in whole body Na(+) turnover rates between the two species (1.1% per day in the European eel versus 19% per day in the rainbow trout) together with the lack of effect of silver exposure on Cl(-) homeostasis in the European eel are hypothesized to be the main reasons for the different silver tolerance observed in the two species.