Morphological and biochemical changes in the gills of Tilapia (Oreochromismossambicus) 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 th e effects of short-term Cd exposure on the cellular function of gill chlori de cells. Gills were sampled after 3 and 7 days exposure. The accumulated C d concentration in gills was analyzed using a graphite furnace atomic absor ption spectrophotometer while the morphological changes of pavement and chl oride cells were examined using scanning and transmission electron microsco pes. 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 /m m(2)) and apical membrane area (11.57-46.32 mu m(2)) in chloride cells, ind icating an adaptational modification of the cell morphology in assisting ga seous transfer and Ca2+ uptake, respectively. However, biochemical analyses of the gill tissues enumerated a decrease in both the activities of alkali ne and high-affinity Ca2+-ATPases. This indicated a reduction in the Ca2+-t ransport capacity per unit chloride cell, suggesting chloride cells being t he primary target of Cd which subsequently lead to fish hypocalcemia. (C) 2 000 Elsevier Science B.V. All rights reserved.