Gill cellular changes induced by copper exposure in the South American tropical freshwater fish Prochilodus scrofa

The cellular changes in gill tissue induced by exposure to copper were studied in the tropical freshwater fish Prochilodus scrofa, with emphasis on chloride and pavement cells. Damage to gills included epithelial changes such as lifting, rupture, peeling of lamellar epithelium, lamellar fusion, hyperplasia, and cellular hypertrophy. Cell degeneration by necrosis and apoptosis was intense in fish exposed to 25 and 29 microg Cu L-1. Pavement cells showed microridge reduction on their surface. Chloride cells proliferated in the lamellar epithelia close to the onset of the lamellae. However, no changes in total chloride cell density in contact with the water were observed. The chloride cell apical area of fish exposed to copper increased, but only fish exposed to 25 microg Cu L-1 showed significant increase in the chloride cell fractional area. At this water copper concentration, almost 60% of the chloride cells were apoptotic. Necrotic chloride cells increased with copper in water, reaching 70% in fish exposed to 29 microg Cu L-1 (=LC50 calculated for this species). Pavement and chloride cell proliferation and hypertrophy on lamellar epithelia increased the thickness of the water-blood barrier. Our findings suggest severe impairment of ion regulation and gas transfer of fish exposed to copper.