Branchial versus intestinal silver toxicity and uptake in the marine teleost Parophrys vetulus

Exposure to elevated waterborne silver as AgNO3 (4.07 muM = 448 mug 1(-1)) in seawater resulted in osmoregulatory disturbance in the lemon sole (Parop hrys vetulus). The main effects were increased plasma Na+ and Cl- concentra tions which translated into increased plasma osmolality. Plasma Mg2+ levels were also slightly increased after 96 h exposure. Using radioisotopic flux measurements, a 50% reduction in branchial unidirectional Na+ extrusion wa s observed after 48 h silver exposure. By applying an intestinal perfusion approach, we were able to separate and thus quantify the intestinal contrib ution to the observed silver-induced physiological disturbance and internal silver accumulation. This analysis revealed that the intestinal contributi on to silver-induced ionoregulatory toxicity was as high as 50-60%. In mark ed contrast, internal silver accumulation (in liver and kidney) was found t o be derived exclusively from uptake across the gills. Drinking of silver-c ontaminated seawater resulted in substantial silver accumulation in the int estinal tissue (but apparently not silver uptake across the intestine), whi ch probably explains the intestinal contribution to silver-induced physiolo gical disturbance.