Relationship between exposure duration, tissue residues, growth, and mortality in rainbow trout ( Oncorhynchus mykiss) juveniles sub-chronically exposed to copper

Abstract

We conducted a 56-day sub-chronic test on the effects of Cu on rainbow trout ( Oncorhynchus mykiss) fry at a nominal water hardness of 100 mg l −1 (as CaCO 3). Response measures were growth, whole body Cu concentrations, and mortality. Significant mortality was observed in fish exposed to 54.1 μg Cu l −1 (47.8%) and 35.7 μg Cu l −1 (11.7%). Growth was dose-dependent over the range of Cu treatments (0–54 μg Cu l −1), and was modeled as a function of Cu exposure concentration and exposure duration. Calculated inhibition concentrations (based on change in wet weight through a 56-day Cu exposure) were IC 50=54.0 μg Cu l −1, IC 20=21.6 μg Cu l −1, IC 10=10.8 μg Cu l −1, and IC 01=1.1 μg Cu l −1. Measured whole body Cu was also dose-dependent, and growth of trout fry was readily modeled as a function of tissue Cu and exposure duration. This model was virtually identical to a model previously developed for rainbow trout exposed to Cu at a hardness of 25 mg l −1. Following the 56-day exposure period, we performed a 96-h acute challenge to Cu and Cd to evaluate the effects of Cu acclimation on acute Cu and Cd toxicity. Sensitivity to Cu was dependent on the ‘acclimation dose’; trout previously held in control aquaria (i.e. not acclimated to Cu) suffered over 80% mortality, whereas trout previously exposed to 35.7 μg Cu l −1 for 56 day suffered 20% mortality. These fish also showed somewhat reduced sensitivity to Cd, suggesting acclimation to Cu can enhance tolerance to other metals. Finally, the relationship between growth response and hardness (derived from several studies) appeared to have a different slope than the hardness relationship previously observed for lethality responses.