Effect of water‐borne zinc on osmoregulation in the freshwater amphipod Gammarus pulex (L.) from populations that differ in their sensitivity to metal stress

<jats:p> <jats:bold>1.</jats:bold> Although there is some evidence that exposure to heavy metals can disrupt osmoregulation in crustaceans, most studies have been carried out on relatively pollution‐tolerant, marine or estuarine species. Consequently the effects of water‐borne zinc (Zn) on osmoregulation by the freshwater amphipod, <jats:italic>Gammarus pulex</jats:italic> (L.), from two populations that differ in their heavy metal sensitivity, have been compared.</jats:p><jats:p> <jats:bold>2.</jats:bold>‘Clean’ site animals (Clowne, Derbyshire) exhibited a marked haemoconcentration (after 4 days at 37·0 μmol Zn l<jats:sup>–1</jats:sup>, 5 days at 18·2 μmol Zn l<jats:sup>–1</jats:sup>) shown by an increase in haemolymph osmotic pressure (OP<jats:sub>h</jats:sub>) and [Na<jats:sup>+</jats:sup>] and [K<jats:sup>+</jats:sup>]. However, after 5 days at 37·0 μmol Zn l<jats:sup>–1</jats:sup>, haemolymph of survivors exhibited an OP<jats:sub>h</jats:sub> significantly less than controls. ‘Contaminated’ site animals showed a reduction in OP<jats:sub>h</jats:sub> (but not ions) only after 5 days at 76·2 μmol Zn l<jats:sup>–1</jats:sup>.</jats:p><jats:p> <jats:bold>3.</jats:bold> There were differences in the threshold and nature of osmoregulatory response to Zn between animals from ‘clean’ and ‘contaminated’ sites, but only at concentrations in excess of those (a) known to affect growth and reproduction in ‘clean’ site animals and (b) occurring at the ‘contaminated’ site. Clearly population differences in physiological capacity and tolerance do exist but their ecological significance is unclear.</jats:p>