Ion regulation in a freshwater crab, Potamonautes warreni: The effects of trace metal exposure.

Abstract

Crustaceans inhabiting metal-contaminated freshwaters are susceptible to toxic insult to their osmoregulatory systems. The main osmoregulatory organs of decapod crustaceans, the gills, are continually bathed in freshwater and are therefore at risk from trace metal impacts. The effects of chronic (21 d) exposure to raised dissolved concentrations of Zn, Cd, Cu and Pb on aspects of hydromineral balance were investigated in Potamonautes warreni, a freshwater crab endemic to rivers in South Africa at potential risk from trace metal contamination from mining operations. Generally, hydromineral balance of P. warreni was tolerant to chronic metal exposures although sublethal cadmium exposure of 860 µg.l-1 for 21 days resulted in a reduced sodium concentration in the haemolymph. A chronic exposure to 43 µg.l-1 cadmium produced an elevated maximum unidirectional sodium uptake, possibly resulting from acclimation to the metal exposure. Branchial Na+/K+-ATPase and V-Type H+-ATPase activity were not affected by chronic in vivo Cd (43 µg.l-1) and Zn (500 µg.l-1) exposures. An important aspect of ameliorating metal toxicity may be through antioxidants and therefore the effects of applying a reducing agent were tested following in vitro metal treatment. Inhibition of Na+/K+-ATPase could be prevented by pre-incubation with a reducing agent, indicating the importance of antioxidants in reducing metal toxicity in this species. Although this study demonstrates the physiological resilience of P. warreni to dissolved trace metal impacts, the energetic consequences of long-term exposure are as yet not known.