Effects of acclimation on the toxicity of stream water contaminated with zinc and cadmium to juvenile cutthroat trout

Abstract

We investigated the influence of acclimation on results of in situ bioassays with cutthroat trout in metal-contaminated streams. Cutthroat trout (Oncorhynchus clarki) were held for 21 days (1) in live containers at a reference or "clean" site having dissolved metals near detection limits (0.01 μg/L cadmium [Cd] and 2.8 μg/L zinc [Zn]; hardness 32 mg/L as CaCO3) and (2) at a site in a mining-impacted watershed having moderately increased metals (0.07 μg/L Cd and 38 to 40 μg/L Zn; hardness 50 mg/L as CaCO3). The 96-hour survival of each treatment group was then tested in situ at five sites from September 5 to 9, 2002, and each group exhibited a range of metal concentrations (0.44 to 39 μg/L arsenic [As], 0.01 to 2.2 μg/L Cd, and 0.49 to 856 μg/L Zn). Survival was 100% at three sites for both treatments. However, a higher percentage of metal-acclimated fish survived at the site with the second highest concentrations of Cd and Zn (0.90 and 238 μg/L, respectively) compared with fish acclimated at the reference site (100% vs. 55%, respectively). Survival was 65% for acclimated fish and 0% for metal-naïve fish at the site with the largest metal concentrations (2.2 μg/L Cd and 856 μg/L Zn). Water collected from the site with the largest concentrations of dissolved metals (on October 30, 2002) was used in a laboratory serial dilution to determine 96-hour LC50 values. The 96-hour LC50 estimates of naïve fish during the in situ and laboratory experiments were similar (0.60 μg Cd/L and 226 μg Zn/L for in situ and 0.64 μg Cd/L and 201 μg Zn/L for laboratory serial dilutions). However, mortality of naïve cutthroat trout tested under laboratory conditions was more rapid in dilutions of 100%, 75%, and 38% site water than in situ experiments. © 2007 Springer Science+Business Media, LLC.