Investigating copper acclimation in mummichog; Implications for ionoregulation and physiological tolerance

Abstract

At elevated concentrations, copper (Cu) disrupts osmoregulation in aquatic organisms. Acclimation can occur at sublethal concentrations, though responses may be species-specific, and mechanisms remain unclear. This study investigated osmoregulatory effects of acute Cu exposure in Fundulus heteroclitus, and whether acclimation mitigates toxicity. Fish were acclimated in seawater to 0 or 0.1 mg/L Cu for 7 d, then euthanized or exposed to 0-2 mg/L Cu for 48 h. Muscle moisture (MM) and tissue Na were measured as osmoregulatory status indicators. Acclimation nor exposure significantly affected MM. Acclimation and acute exposure significantly affected tissue Na in acutely exposed fish, with an increase at 2 mg/L and lower levels in acclimated fish overall. Findings suggest Cu acclimation may alleviate ionoregulatory disruptions observed at higher acute exposure concentrations, but does not fully mitigate toxicity. Preliminary in vitro data indicate Na⁺/K⁺-ATPase activity declines with increasing Cu, warranting further investigation on Na⁺/K⁺-ATPase desensitization in Cu acclimation.