Exposure of rainbow trout (Oncorhynchus mykiss) to nonylphenol is associated with an increased chloride cell fractional surface area

Nonylphenol is a biodegradation product of a widely used group of non-ionic detergents. Because of its ubiquitous distribution and persistence, nonylp henol is present in surface waters as a pollutant. Little is known about it s biological effects at environmentally relevant concentrations other than its action as a xenoestrogen. The goal of the present paper was to study th e trout gill surface epithelium as the major interface between fish and wat er in view of possible morphological alterations due to exposure to monylph enol. Rainbow trout were intermitently exposed to 10 mu g/l nonylphenol and gill samples from experimental and control animals were investigated by sc anning electron microscopy. Gill surface epithelium was scrutinised for cha nges in chloride cell density and their status regarding cell surface modif ications. In addition, chloride cell fractional surface area (CCFA) was det ermined by morphometrical methods. Statistical analysis revealed a highly s ignificant increase of CCFA in animals exposed to nonylphenol as compared t o control animals (P = 0.0001). Semi-quantitative assessment of their param eters suggested a higher chloride cell density and a larger proportion of c hloride cell density and a larger proportion of chloride cells bearing micr ovilli. Taken together, these results provide evidence that exposure of tro ut to nonylphenol is associated with a substantial increase in the active i nterface of chloride cells with water. We interpret these findings as being a means to further the fish's capacity for calcium exchange.