The effects of long-term cadmium exposure on the growth and survival of juvenile bull trout ( Salvelinus confluentus)

Abstract

Bull trout ( Salvelinus confluentus) have been listed recently as threatened in the United States under the federal Endangered Species Act. This species currently resides, or historically resided, in several waterways that either are impacted or are under threat of impact from metals mining activities. We conducted a 55-day sub-chronic (i.e. sublethal) cadmium (Cd) exposure in water at 30 mg l −1 (as CaCO 3) hardness, pH 7.5, and 8 °C. Exposures were conducted using six replicate exposure tanks for each of the six treatments (five Cd concentrations and one control). Measured Cd concentrations were <0.013 (control), 0.052, 0.089, 0.197, 0.383, and 0.786 μg Cd l −1. Exposure to 0.786 μg Cd l −1 caused increased mortality (37%) and reduced growth (28% reduction in weight change) in fish exposed for 55 days. All Cd exposure concentrations caused significant whole body accumulation of Cd compared with controls. Our results indicate that even though fish are significantly accumulating Cd in each non-control treatment, growth reductions in bull trout occurred only at Cd concentrations that also caused significant mortality. The Cd concentration that reduced growth and survival in this long-term exposure (0.786 μg Cd l −1) is greater than the recently-revised US federal aquatic life criteria (ALC) value for the corresponding hardness concentration (ALC=0.62 μg Cd l −1 for acute effects and 0.11 μg Cd l −1 for chronic effects).