Physiological effects of chronic copper exposure to rainbow trout (Oncorhynchus mykiss) in hard and soft water: Evaluation of chronic indicators

Effects of chronic copper exposure on a suite of indicators were examined: acute toxicity, acclimation, growth, sprint performance, whole-body electro lytes, tissue residues, and gill copper binding characteristics. Juvenile r ainbow trout were exposed for 30 d to waterborne copper in hard water (hard ness = 120 mg/L as CaCO3, pH = 8.0, Cu = 20 and 60 mug/L) and soft water (h ardness = 20 mg/L as CaCO3, pH = 7.2, Cu = 1 and 2 mug/l). Significant accl imation to the metal occurred only in fish exposed to 60 mug/L, as seen by an approx. twofold increase in 96-h LC50 (153 vs 91 mug Cu/L). Chronic copp er exposure had little or no effect on survival, growth, or swimming perfor mance in either water hardness, nor was there any initial whole-body electr olyte loss (Na+ and Cl-). The present data suggest that the availability of food (3% wet body weight/day, distributed as three 1% meals) prevented gro wth inhibition and initial ion losses that usually result from Cu exposure. Elevated metal burdens in the gills and livers of exposed fish were measur es of chronic copper exposure but not of effect. Initial gill binding exper iments revealed the necessity of using radiolabeled Cu (Cu-64) to detect ne wly accumulated Cu against gill. background levels. Using this method, we v erified the presence of saturable Cu-binding sites in the gills of juvenile rainbow trout and were able to make estimates of copper-binding affinity ( log K-gill=Cu) and capacity (B-max). Furthermore, we showed that both chron ic exposure to Cu and to low water calcium had important effects on the Cu- binding characteristics of the gills.