Avoidance responses of schooling fathead minnows (Pimephales promelas) to a blend of metals during a 9-month exposure

Avoidance of a blend of four metals (relative proportions: 1.00 copper, 0.54 chromium, 1.85 arsenic, 0.38 selenium) was determined in fathead minnows (Pimephales promelas) in a steepgradient, laminar-flow chamber. Avoidance responses were determined seasonally during 12 months of laboratory observation for unexposed (control) and metals-exposed fish. Unexposed fish avoided very low concentrations of the blend (29 μg/L total metals). Fish exposed to 98 μg/L total metals preferred elevated concentrations equal to three times the holding exposure concentration (294 μg/L total metals) after 3 months of exposure, mildly avoided concentrations five times the holding exposure concentration (490 μg/L total metals) after 6 months of exposure and were not responsive to concentrations approaching ten times the holding exposure level (980 μg/L total metals) after 9 months of exposure. Activity, as measured by movements per unit time in the avoidance tests, was not affected by long-term exposure or during testing.