Toxic effects of three mercurial compounds on survival, and histology of the kidney of the catfish Clarias batrachus (L.).

In Clarias batrachus methylmercuric chloride (CH3HgCl) was 1.18 and 10.05 times more toxic than mercuric chloride (HgCl2) and emisan 6 (methoxyethyl mercury chloride), respectively, for 96 hr. A similar trend was observed at 24, 48, and 72 hr. Exposure of the catfish to sublethal concentrations of these mercurials for 14 and 28 days caused progressive changes in the kidney. The diameter of the proximal convoluted tubules was increased, the epithelial cells were hypertrophied, and the lumen was reduced and filled with secretory material and sloughed-off cells. In 14-day emisan 6-treated fish, some glomeruli were also degenerated. Exposure of the catfish to toxicologically safe concentrations of the mercurials for 90 days caused vacuolation, atrophy, and extensive damage of the tubules in HgCl2-and CH3HgCl-treated fish, and hypertrophy and vacuolation of epithelial cells of some tubules in the emisan 6-treated fish. Regeneration was noticed in the 90-day HgCl2-exposed group. After 180 days of exposure, however, histology of the kidney appeared normal in all the groups.