CELLULAR-RESPONSES IN THE SKIN OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) EXPOSED TO RHINE WATER

Trout, Oncorhynchus mykiss, were exposed to water from the Rhine for 24 days and their skin examined by light and electron microscopy. Relative to control fish mitotic figures were common and seen throughout the epidermis. Pavement cells in fish exposed to Rhine water contained significantly more secretory vesicles than control fish. Necrotic pavement cells were apparent after 24 h, and apoptotic cells from day 4 on. Mucous secretion was intense and the differentiation of mucous cells was stimulated. Some of these cells synthesized mucus of high electron density, probably of a serous composition. Leucocytes invaded the dermis and epidermis, and towards the end of the experiment many apoptotic and necrotic lymphocytes were found. In the dermis fibroblasts were abundant and actively producing collagen. Pigment containing cytoplasmic extensions of melanocytes penetrated into the epidermis. after 14 and 24 days of exposure many pigment cells, melanocytes, iridocytes and xanthocytes became apoptotic. Most of these changes are known from fish exposed to heavy metals, acid water or other stressful treatments, indicating that exposure to Rhine water is a stressful experience for trout.