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 2 4 days and their skin examined by light and electron microscopy. Relat ive to control fish mitotic figures were common and seen throughout th e epidermis. Pavement cells in fish exposed to Rhine water contained s ignificantly more secretory vesicles than control fish. Necrotic pavem ent 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 der mis and epidermis, and towards the end of the experiment many apoptoti c and necrotic lymphocytes were found. In the dermis fibroblasts were abundant and actively producing collagen. Pigment containing cytoplasm ic extensions of melanocytes penetrated into the epidermis. after 14 a nd 24 days of exposure many pigment cells, melanocytes, iridocytes and xanthocytes became apoptotic. Most of these changes are known from fi sh exposed to heavy metals, acid water or other stressful treatments, indicating that exposure to Rhine water is a stressful experience for trout.