CELLULAR-RESPONSES OF THE SKIN OF CARP (CYPRINUS-CARPIO) EXPOSED TO ACIDIFIED WATER

The skin of carp was examined after exposure to acidified water. Degen erative cells were common in the upper epidermal layers. During the fi rst days most of these cells exhibited signs of necrosis. Later on the incidence of necrosis decreased and that of apoptosis increased. In t he acid-exposed fish, the upper filament cells and pavement cells prod uced secretory vesicles of high electron density, some of which showed peroxidase activity. This enzyme activity was also present in the gly cocalyx covering these cells, and in the cytoplasm of apoptotic cells. Mitotic figures and newly differentiating mucous cells were common in the outer epidermal layers. Mucous cells became elongated and produce d mucosomes of high electron density. Mucosomes with peroxidase activi ty were also found. Club cells increased in number. Chloride cells and solitary chemo-sensory cells, not seen in the controls, appeared in t he upper epithelial layer. The skin was invaded by many leucocytes and by pigment-containing cytoplasmic extensions of melanocytes. Some leu cocytes apparently penetrated into the club cells. These structural ob servations reflect the complexity of the physiological response of the skin to acid water.