Morphological and morphometric changes in the gills of mosquitofish ( Gambusia holbrooki) after exposure to mercury (II)

• Published in: Aquatic toxicology 1996, Vol.34 (2), p.163-183
• Main Authors: Jagoe, Charles H., Faivre, Amy, Newman, Michael C.
• Format: Article
• Language: English
• Subjects: Autometallography; Chloride cells; Gambusia holbrooki; Gill epithelium; Mercury; SEM; Stereology
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/0166-445X(95)00033-Z

Physiological measurements suggest that mercury (Hg) affects ion regulation in aquatic organisms. This implies that Hg should cause morphological changes in gills, the major ionoregulatory organ of fish. Previous studies have shown severe Hg-induced gill damage at acutely lethal Hg concentrations, but in soft fresh waters, where ionoregulatory disturbances should be most pronounced, there have been no quantitative studies to date of the effects of dissolved Hg at sublethal concentrations. We exposed mosquitofish ( Gambusia holbrooki) to nominal concentrations of 75, 150 and 300 nM Hg (II) in natural stream water of low ionic strength (Ca = 4.8 μM) in a static-renewal experiment. Mercury concentrations dropped rapidly after Hg additions, and most dissolved Hg was probably complexed with humic substances. Gills were sampled after 7 and 14 days exposure. Examination with scanning electron microscopy (SEM), indicated that Hg caused progressive loss of secondary lamellae and loss of cell surface microridges. Effects became more severe at higher Hg concentrations. Using light microscopy and morphometric techniques, the percent of gill filament occupied by chloride cells (volume density) was significantly greater in all Hg treatments than in controls, and thickness of the primary lamellar epithelium increased with Hg exposure. Thickening of the primary lamellar epithelium filled some interlamellar spaces, obliterating secondary lamellae. However, width of the exposed portions of secondary lamellae was not affected by Hg, suggesting that blood-to-water diffusion distances did not increase in response to Hg exposure. Autometallographic staining for Hg showed that the metal was distributed throughout the gill epithelium, and not concentrated inside chloride cells.