The mechanisms and costs of physiological and toxicological acclimation to waterborne silver in juvenile rainbow trout (Oncorhynchus mykiss)

F. Galvez, McMaster University
C. M. Wood, McMaster University

Abstract

Juvenile rainbow trout were exposed to 0, 0.1, 1, 3, and 5 μg/l silver (Ag, as AgNO3) for 23 days. Specific growth rate, cumulative food consumption, food-conversion efficiency, and critical swimming speed (Ucrit) were significantly reduced during 5 μg/l Ag exposure, demonstrating a physiological cost of silver acclimation. Only the 5 μg/l Ag treatment had significant cumulative mortality (5.2%). Fish were most susceptible to silver on days 5 and 15. Exposure to 5 μg/l Ag significantly lowered plasma Na+ and Cl- on days 5 and 10, but plasma ion concentration recovered thereafter. Unidirectional Na+ uptake and gill Na/K-ATPase activity were significantly inhibited by 3 and 5 μg/l Ag exposure. Na+ uptake was inhibited by 3 μg/l Ag at day 5 alone, whereas the effects at the highest Ag exposure persisted until day 15. Gill Na/K-ATPase was inhibited on day 5 in both the 3 and 5 μg/l Ag treatments but increased to approx. 1.5 times of control levels by day 23. Only the 3 and 5 μg/l Ag treatments produced toxicological acclimation (at least twofold elevations in 168-h LC50 values in fish subsampled on days 15 and 23). We conclude that physiological acclimation results from compensatory changes in Na+ transport at the gills, and that these changes may eventually lead to toxicological acclimation.