UPTAKE OF MERCURY BY THE GILLS OF THE FRESH-WATER CHINESE CRAB ERIOCHEIR-SINENSIS (MILNE-EDWARDS)

An in vitro perfused preparation of gills isolated from the euryhaline Chinese crab Eriocheir sinensis has been used to investigate the upta ke of mercury. The results show that mercury crosses the epithelio cut icular complex of the anterior respiratory gills and of the posterior salt-transporting gills. Mercury passes down its concentration gradien t and it may reasonably be concluded that the heavy metal enters the c rab via diffusion. However, the mercury influx through the epithelio c uticular complex is significantly increased when the concentration gra dient of mercury is nullified by the addition of mercury to the intern al perfusion medium. A mechanism such as exchange-diffusion could then be involved in the transepithelial movements of mercury in crab gills , but this remains a matter of speculation. It is also demonstrated th at the metabolic inhibitor 2,4-dinitrophenol, applied in the perfusion medium, drastically and immediately inhibits the influx of mercury th rough the anterior gills, substantiating the idea that a mechanism req uiring metabolic energy is involved in the transepithelial movements o f mercury. The nature of the non-diffusional component of mercury tran sport remains a matter of controversy.