Mercury and osmoregulation in the euryhaline crab, Eriocheir sinensis

This review will focus on cases where it might be possible that the toxicity of the heavy metal mercury results from an interaction with osmoregulatory mechanisms. It is shown that mercury-induced impairment of osmoregulatory capability in the sense of severe modifications of the blood osmotic concentration is more pronounced in brachyuran decapod species adapted to dilute waters. The rationale for considering these effects is based on a comparison between mercury effects on three species of decapod crustaceans exhibiting various degrees of osmoregulation capability: the strong regulator crab Eriocheir sinensis, the weak regulator Carcinus maenas, both of them being euryhaline, and the stenohaline osmoconformer Cancer pagurus. It is established that a synergistic effect exists between salinity and HgCl2 toxicity in euryhaline species which are hyperregulators in dilute media, that is, E. sinensis and C. maenas only. Depth study of E. sinensis as a model demonstrates that Na+ and Cl− permeabilities of the gill epithelium is affected by mercury, as well as the Na+ and Cl− active transport processes located at the same level. Evidences are brought showing that mercury drastically disturbs the Na+/K+ pump and the Cl− channels located in the serosal baso-lateral membranes of the posterior gills.