Effects of copper exposure on growth and survival of juvenile bull trout

Metal toxicity from mine wastes has been identified as a potential contributor to declining populations of the federally threatened bull trout Salvelinus confluentus. Although several studies have been published on the effects of long-term Cu exposure on growth in salmonid fish, none have been conducted with bull trout. We evaluated the effects of a 60-d Cu exposure on bull trout in water at 220 mg/L hardness (as CaCO3) and pH 7.9. The endpoints measured were growth, whole-body Cu concentration, and mortality. Exposure to Cu at 179 mug/L resulted in 7% mortality (compared with a mortality of 2% in controls), but no effects of Cu exposure on growth were observed at any Cu concentration tested. Measured tissue residues of Cu in these bull trout were higher than those associated with reduced growth in rainbow trout Oncorhynchus mykiss, indicating that bull trout may be more tolerant of long-term Cu exposure than rainbow trout. This greater tolerance to Cu may be associated with a lower rate of Cu accumulation or the slower overall. growth rate in bull trout than in rainbow trout. Our results indicate that accumulation of whole-body Cu does not predict toxicological effects in this species.