Impact of copper on the structure of gills and epipodites of the shrimp Penaeus japonicus (Decapoda)

The impact of sublethal concentrations of copper on the structure and ultrastructure of gills and epipodites has been studied in late juvenile Penaeus japonicus. The structural changes which occur in the gill and epipodite cells appeared to be a function of copper accumulation in these tissues. The gill cells of shrimps exposed to 100 and 10 mu g Cu l(-1) for 15 days did not display discernible structural changes. However, an increased number of nephrocytes was observed in some gill filaments, especially in shrimps exposed to 100 mu g Cu l(-1). A profound alteration of the gill structure occurred after exposure to 500 and 1,000 mu g Cu l(-1) for 4 days. Exposure to 1,000 mu g Cu l(-1) resulted in gaps between the cuticle and the epithelium and in the disorganization of epithelial cells. The nuclear matrices were condensed and vacuoles were observed around the nucleus. Exposure to 10 mu g Cu l(-1) for 15 days did not result in perceptible structural changes of the epipodite cells. After exposure to 500 and 1,000 mu g Cu l(-1) for 4 days and to 100 mu g Cu l(-1) for 15 days, the epithelial cells of epipodites were completely altered. Basal infoldings were less numerous and apical microvilli were absent. The number and size of mitochondria decreased and their structure was disorganized. The nuclear matrices were condensed, with vacuoles around the nucleus, and the cells became extensively vacuolated. Pseudomyelinic structures were noted in epipodite cells of shrimps exposed to 500 mu g Cu l(-1). The significance of the morphological changes of these organs after exposure to copper are discussed in relation to their physiological functions.