Increased susceptibility to metal mine discharges during thesmolt stage of Atlantic salmon (Salmo salar L.)

摘要

Increased susceptibility during the smolt stage of Atlantic salmon (salmo salar)to low pH and aluminium (Al) is well documented. Inhibition of the Na~+/K~+ATPase (NKA) enzyme activity corresponds with ionoregulatory disruptionswith resulting mortality. Effects on smolts occur at Al doses far below thoserequired to cause effects on parr, and delayed effects in the sea phase areobserved. Whether the increased susceptibility is specific to Al, or represents amore general mechanism is not clear, although recent studies suggest similarresponses to other metals. A pilot experiment to test the effects of acid metalmine discharges (AMD) on the smolt stage of Atlantic salmon was conductedin River Stjordalselva, Norway. Migrating smolts were caught and distributedto experimental cages located at sites influenced by AMD, or at reference sites.Mortality occurred faster in smolts than previously seen in parr at the AMDsites, where mean (± 1 SD) total copper (Cu) and low molecular mass positivelycharged Cu concentrations were 26,2 (±10) and 6,9 (±2) μg/L, respectively.NKA activity was almost completely inhibited within 48 hrs of exposure, andsevere ionoregulatory disruption was observed. Mortality approached 100 %within 48 hrs. This study indicates similar increased susceptibility in Atlanticsalmon smolts exposed to AMD as previously observed for Al. Thus, there isclearly a need to evaluate whether the current Norwegian target concentrationfor mitigation efforts (10 μg Cu/L) is sufficient to ensure protection at this lifestage, and thereby obtain sustainable management of salmon stocks subjected toAMR.