Lethal effects of inorganic mercury on cells and tissues of Trichomycterus brasiliensis (Pisces; Siluroidei).

The uptake of heavy metals like mercury is rapid and tissue and cell pathologies are a consequence of its concentration in water and the time of exposure. For Trichomycterus brasiliensis, inorganic mercury is lethal above 0.1 mg.l(-1) in 24 hours. The gills were severely affected: an increased cell proliferation in the interlamellar regions leads to a thickening of the secondary lamellae. The lamellar fusion is higher 12 hours after exposure. The liver is increasingly damaged: after 4 hours the hepatocytes show hyaline sites around the nuclei proliferation of smooth ER, modified mitochondria and less electron dense nuclei without nucleolus. After 24 hours, necrosis is almost complete and blood comes out of all capillaries. The kidneys are also disorganized and tubule cells decrease in number and change in size, but there is a tendency of tissue recovery after 24 hours. Nerves such as the optic, show disorganized disposition of axons and mainly disruption and dissociation of myelin sheaths, leading to a decrease in motility and coordination. All these results demonstrate that T. brasiliensis is severely affected by inorganic mercury in concentrations that are sublethal for many other species.