Morphological and biochemical changes in the gills of Tilapia (Oreochromis mossambicus) to ambient cadmium exposure

Tilapia, Oreochromis mossambicus, were reared in freshwater and exposed to 40, 80 and 160 ppb ambient cadmium for a period of 7 days to investigate the effects of short-term Cd exposure on the cellular function of gill chloride cells. Gills were sampled after 3 and 7 days exposure. The accumulated Cd concentration in gills was analyzed using a graphite furnace atomic absorption spectrophotometer while the morphological changes of pavement and chloride cells were examined using scanning and transmission electron microscopes. Gill Cd concentration was significantly increased in samples (10.03-44.36 ppb) at 3 and 7 days exposure. Accompanying this was an augmentation of microridge in pavement cells, and an increase in the density (1964-3603 /mm(2)) and apical membrane area (11.57-46.32 µm(2)) in chloride cells, indicating an adaptational modification of the cell morphology in assisting gaseous transfer and Ca(2+) uptake, respectively. However, biochemical analyses of the gill tissues enumerated a decrease in both the activities of alkaline and high-affinity Ca(2+)-ATPases. This indicated a reduction in the Ca(2+)-transport capacity per unit chloride cell, suggesting chloride cells being the primary target of Cd which subsequently lead to fish hypocalcemia.