MP9 Metals and Bioaccumulation
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(HAR-1117-789983) Zinc toxicity to Brown Trout of various chronological ages and stages of acclimation.

Diedrich, D¹, Ranville, J², Ross, P², Harper-Arabie, R¹, Brinkman, S³, Hoff, D⁴, Wall, D⁵, ¹ Western Washington University, Bellingham, Washington, United States² Colorado School of Mines, Golden, Colorado, United States³ Colorado Division of Wildlife, Fort Collins, Colorado, United States⁴ United States Environmental Protection Agency, Golden, Colorado, United States⁵ United States Fish and Wildlife Service, Golden, Colorado, United States

ABSTRACT- Recent studies have indicated that several factors may be involved in the tolerance of Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss) to acute zinc exposure. Acclimation of trout to zinc may allow a greater tolerance to zinc exposure and de-acclimation may induce less tolerance. Additionally, greater chronological age may increase tolerance of S. trutta to acute zinc exposure. Several biomarkers were investigated with the goals being to 1) confirm or discount the results from these prior studies that indicate S. trutta were less tolerant with de-acclimation and more tolerant with acclimation, and/or as chronological age increases; and 2) elucidate the mechanisms involved in these possible acclimation and age-dependent effects. The exposures were conducted in flow-through and static systems at the Colorado Division of Wildlife (CDW). The age of the organisms in the experiments was controlled by varying the water temperatures (3oC, 6oC, 9oC, and 12oC) during the egg and larvae stages. When the fish reached approximately 0.5 grams average weight, they were acclimated to 12oC and exposed to zinc sulfate. Time-to-death data was collected for 96 hours during each of the four exposures. At 24 and 96 hours after exposure, the gills were excised and immediately stored until analysis for total protein content and supplementary bioassays were conducted which included: zinc concentration, metallothionein concentration, and ATPase activity. Proteins in the gill mass were determined by the modified Folin-Lowry method and were used to normalize zinc content, metallothioneins, and ATPase activity. The zinc content in the gill tissue, the metallothionein response and ATPase response were related to the LC50 and the LA50. This comparison will provide a better understanding of the mechanisms behind the changes in tolerance of acclimated, de-acclimated, and different chronological aged O. mykiss and S. trutta if these previous observations are confirmed.

Key words: zinc, brown trout, toxicity, acclimation