Impact of cadmium on the structure of gills and epipodites of the shrimp

The objective of this study was to investigate the impact of cadmium on the structure of gills and epipodites in late juvenile Penaeus japonicus. Cadmium titrations were performed by atomic absorption flame spectrophotometry, and structural observations were performed through light- and electron-microscopy. The cadmium concentration increased in different tissues (mainly gills, epipodites and hepatopancreas) according to the external cadmium concentration and the exposure time. The structural changes which occurred in the gill and epipodite cells appeared to be a function of cadmium accumulation in these tissues. Gill cells of shrimps exposed to 2 and 200 μg Cd·L−1 for 15 d did not display discernible structural changes. An increased number of nephrocytes was noted in gill filaments of shrimps exposed to 200 μg Cd·L−1. Exposure to 2 000 and 4 000 μg Cd·L−1 during 4 d resulted in profound structural changes. The epithelial cells were necrosed, disorganized and vacuolized. Exposure to 2 μg Cd·L−1 for 15 d did not result in discernible structural changes of epitodite cells. Exposure to 200 μg Cd·L−1 for 15 d, 2 000 and 4 000 μg Cd·L−1 during 4 d induced profound alterations of the epipodites: increased thickness, decreased number of apical microvilli, basal infoldings and mitochondria, occurrence of pseudomyelinic structures. These alterations are discussed in relation to the respiratory and osmoregulatory functions of gills and epipodites.