IMIS

Previous research showed that the spiny dogfish, Squalus acanthias, is much more sensitive to silver exposure than typical marine teleosts. The aim of the present study was to investigate if spiny dogfish were equally sensitive to copper exposure and whether the toxic mechanisms were the same. We exposed cannulated and non-cannulated spiny dogfish to measured concentrations of Cu (nominally 0, 500, 1000 and 1500 µg L^-1 Cu) for 72–96 h. All Cu exposures induced acidosis and lactate accumulation of either a temporary (500 µg L^-1) or more persistent nature (1000 and 1500 µg L^-1). At the two highest Cu concentrations, gill Na⁺/K⁺-ATPase activities were reduced by 45% (1000 µg L^-1) and 62% (1500 µg L^-1), and plasma Na⁺ and Cl^- concentrations increased by approximately 50 mM each. At the same time urea excretion doubled and plasma urea dropped by 100 mM. Together with plasma urea, plasma TMAO levels dropped proportionally, indicating that the general impermeability of the gills was compromised. Overall plasma osmolarity did not change.

Cu accumulation was limited with significant increases in plasma Cu and elevated gill and kidney Cu burdens at 1000 and 1500 µg L^-1. We conclude that Cu, like Ag, exerts toxic effect on Na⁺/K⁺-ATPase activities in the shark similar to those of teleosts, but there is an additional toxic action on elasmobranch urea retention capacities. With a 96 h LC₅₀ in the 800–1000 µg L^-1 range, overall sensitivity of spiny dogfish for Cu is, in contrast with its sensitivity to Ag, only slightly lower than in typical marine teleosts.