PHYSIOLOGICAL-RESPONSES OF JUVENILE RAINBOW-TROUT TO CHRONIC LOW-LEVEL EXPOSURES OF WATERBORNE SILVER

The physiological effects of chronic exposure to AgNO3 in moderately h ard freshwater were investigated in juvenile rainbow trout (Oncorhynch us mykiss Walbaum). Two separate 28-day exposures were performed at si lver concentrations of 0.5 and 2.0 mu g/L in flowing Hamilton dechlori nated tap water. Exposure to 0.5 mu g/L Ag resulted in a slight increa se (similar to 14.9%) in food consumption, whereas growth rates remain ed unaltered. Both plasma Na+ and Cl- levels were significantly decrea sed by 11.8% and 9.3%, respectively at day 16 of the exposure. Hepatic Ag concentrations were elevated approximately 4-fold in 0.5 mu g/L Ag -exposed fish. However, no significant increases in liver metallothion ein (MT) concentrations were noted. No mortalities were observed durin g this 28-day exposure. In comparison, chronic exposure to 2.0 mu g/L Ag resulted in a 28.8% decrease in food consumption and a 43.0% reduct ion in growth rate. Plasma [Na+] was decreased by 18.3%, whereas plasm a [Cl-] was reduced by 12.2% at day 7. At both concentrations of silve r, plasma ion concentrations appeared to recover thereafter. Silver ac cumulated steadily in the liver up until day 15 when concentrations we re 39.7 mu g/g wet weight (285-fold increase) above control levels. In addition, MT levels were increased by 81.2% at day 7. Silver exposure at 2.0 mu g/L resulted in approximately 15.0% mortality over the 28-d ay period. (C) 1998 Elsevier Science Inc.