A stereological study of copper toxicity in gills of Oreochromis niloticus

Stereological methods were used to estimate the volumetric density (VV) of the filamentar epithelium (FE, 39%), lamellae (L, 28%), central venous sinus (CVS, 14%), central axis (16%), mucous cells (MC, 2%) and chloride cells (CC, 1%) in the gill filament of control Nile Tilapia. The relative volumes of FE and L, and the relative volumes of CVS and central axis, varied inversely under exposure to copper, with high copper toxic levels declanching a chronic defence mechanism that was, nevertheless, overcome, and low copper toxic levels causing adaptation within a moderate acute phase type of response. Copper also induced a decrease of the VV (MC, gill filament) due to reduction of surface MC, despite the marked increase of stem MC at chronic exposure to high copper toxic levels. Diminution of the numerical density of filamentar CC was responsible for the decreased VV (CC, gill filament), although lamellar CC significantly increased at chronic exposure to low copper toxic levels. The present results demonstrate that cell relative volumes, mean volumes and numerical densities are dependent on the variations of the FE and L, which without a quantitative approach may be misinterpreted, thus stressing the importance of using stereological tools for analyzing histopathological patterns.