Acute effects of cadmium on osmoregulation of the freshwater teleost Prochilodus lineatus: Enzymes activity and plasma ions

• Cd effects were evaluated on plasma ions and ATPases of Prochilodus lineatus.
• Fish were exposed to 1 and 10 μg Cd L−1 for 24 and 96 h.
• Na+/K+-ATPase and carbonic anhydrase decreased in gills and kidney after Cd exposure.
• Gill Ca2+-ATPase and plasma Ca2+ decreased after Cd exposure.
• Cd concentrations set by Brazilian guidelines affect Ca2+ regulation of P. lineatus.

Cadmium (Cd) is a trace element that is very toxic to fish. It is commonly found in surface waters contaminated with industrial effluents. When dissolved in water, Cd can rapidly cause physiological changes in the gills and kidneys of freshwater fish. The objective of this study was to evaluate the acute effects of Cd on the osmoregulation of the Neotropical fish Prochilodus lineatus. Juvenile fish were exposed to Cd at two concentrations [1 (Cd1) and 10 (Cd10) μg L−1] for 24 and 96 h. The effects of Cd were evaluated through the analysis of ions (Na+, K+, Ca2+, and Cl−) and plasma osmolality, and by measuring the activities of enzymes involved in osmoregulation obtained from the gills and kidney. Fish exposed to Cd for 24 and 96 h showed a decrease in Na+/K+-ATPase activity in the gills and kidney. The activity of carbonic anhydrase decreased in the gills after 24 h and in both tissues after 96 h of Cd exposure. The gill Ca2+-ATPase activity also decreased with Cd exposure, with a concomitant drop in the plasma concentration of Ca2+. Despite the hypocalcemia, there were no changes in the concentration of the ions Na+, K+, and Cl− or in plasma osmolality. Among the enzymes involved in ion transport, H+-ATPase was the only enzyme that showed increased activity in gills, whereas its activity in kidney remained unchanged. The results of this study demonstrate that waterborne Cd at the maximum concentrations set by Brazilian guidelines for freshwater affects the gills and kidney functions of P. lineatus. Acute exposure to Cd resulted in the decrease of the activity of enzymes, which culminated with the loss of the fish's ability to regulate the levels of calcium in the blood, leading to hypocalcemia.