CORTISOL INDUCES STRESS-RELATED CHANGES IN THE SKIN OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The ultrastructure of the skin of rainbow trout, Oncorhynchus mykiss, was studied over a 7-day period after a single meal containing cortiso l. The fish experienced increased plasma cortisol levels for 1 day. Pa vement cells contained significantly more vesicles of high electron de nsity, which were also numerous in deeper filament cells, and displaye d peroxidase activity. Mitotic cells were common after 4 and 7 days. I ncreased apoptosis, taken to indicate accelerated ageing, was detected in both pavement and mucous cells. Newly differentiated mucous cells were found close to skin surface, and many mucous cells contained muco somes of high electron density. The basal lamina became highly folded. The low numbers of leukocytes present in the skin did not change noti ceably, but substantially more lymphocytes were apoptotic. The melanos omes in the pigment initially dispersed and subsequently reaggregated in the cell bodies of these cells. The reaggregation was accompanied b y apoptosis of melanocyte extensions. The results demonstrate the abil ity of the hormone to regulate several of the effects observed in the skin of fish challenged by stressors. Other phenomena generally observ ed in stressed fish, such as pavement cell necrosis and massive leucoc yte infiltration, were not found after cortisol treatment. The latter observation indicates that regulatory factors in addition to cortisol must be operative during stress. (C) 1995 Academic Press. Inc.