Avoidance of Copper and Nickel by Rainbow Trout as Monitored by a Computer-Based Data Acquisition System

Abstract

The avoidance response of rainbow trout Salmo gairdneri to copper and nickel solutions under several exposure regimes was evaluated with a computer-based data acquisition system interfaced with a linear, plexiglass chamber with countercurrent water flow. The best estimates of the avoidance thresholds for these metals were 6.4 μg/liter total copper and 23.9 μg/liter total nickel (95% confidence limits were 2.6–15.5 and 10.2–54.3 μg/liter, respectively). For each metal, avoidance threshold concentrations were not different whether fish were exposed in shallow or steep concentration gradients. Also, no significant differences (P > 0.05) were found when fish received multiple, increasing exposures or a single exposure in steep-gradient conditions. Rainbow trout initially avoided low copper concentrations, but were attracted to higher ones (330–390 μg/liter) during shallow-gradient tests. Under similar test conditions, fish were attracted to low nickel concentrations (about 6 μg/liter), but avoided higher levels (> 19 μg/liter). The 24-hour average concentration of these two metals presently considered adequate for the protection of freshwater aquatic life fell within the 95% confidence limits for threshold avoidance concentrations reported here. This suggests that environmental impacts predicted on the basis of toxicity tests alone do not reflect potentially important behavioral changes caused by subchronic concentrations of copper and nickel. Avoidance tests, therefore, may prove to be a valuable tool for screening toxic chemicals, providing additional information and a broader perspective for evaluating the impact of aquatic contaminants on fishery resources. The results indicate that the steep gradient, in which a single fish is exposed to several consecutively increasing doses, provides the simplest means of exposure, yielding easily quantified information amenable to statistical analysis. The computer-based system also provides a rapid, easy-to-operate, accurate, and relatively inexpensive means of collecting avoidance data.