Cellular responses of the skin and changes in plasma cortisol levels of trout ( Oncorhynchus mykiss ) exposed to acidified water

Abstract

A ïstract. The skin structure and the plasma cortisol leve of trout, Oncorhynchus m ykiss, were examined durii : 7 days of exposure to water of pH 5. By day-4 and -7 the thickness of the epidermis was significantly (/ <0.05) less in acid exposed fish than in controls, and cl generative cells were common in the upper epidermal I; ers. Many epidermal cells exhibited signs of necrosis, a 1 by day-7 many apoptotic cells were also present. Seci tory vesicles of high electron density were abundant h the filament cells of the 3-4 outermost layers of epid mis, and intercellular spaces had increased. Mitotic Il Lires occurred throughout the epidermis, with the exc uion of the outermost cell layer. Mucous cells became e »ngated after day-1, and later, newly differentiating n icous cells could be seen close to the skin surface, and n my mucocytes contained mucosomes of high electron d isity. Rodlet cells were occasionally seen. Chloride c Is appeared similar to those of control fish. Many leuc cytes, mainly macrophages and lymphocytes, had pene ated the epidermis via the highly undulating basal k nina, and at day-7, numerous apoptotic lymphocytes w re found. In the dermis, melanosomes became disp rsed in the cytoplasmic extensions of melanocytes w lich were present in the epidermis of all acid-exposed fi h. Iridocytes were rare after day-4, while fibroblasts w re abundant and secreted larçe amounts of collagen. A ter 1 day of exposure to acidified water, a significant (/ <0.05) elevation of the plasma cortisol level had occ rred, but this subsequently declined, and had returned u control values by day-7. The changes in skin struce, however, remained throughout the whole exposure period.

Responses of skin mucous cells to aluminium exposure at low pH in Atlantic salmon (Salmo salar) smolts

“…The reduction in number of mucous cells is probably the result of exhaustion of the mucous cells caused by extensive mucus secretion (Iger et al 1988(Iger et al , 1994Roy 1988). The strong decrease in skin mucous cells was associated with a general mucification of gills and skin, and this indicates that the number of skin mucous cells is a good parameter for quantifi cation of mucus secretion.…”

“…The observed increase in mucous cell numerical densities in these studies might reflect a proliferation of immature mucous cells which is not dominated by a loss of mucous cells due to a massive discharge of their contents. Iger et al (1994) de scribed a first-phase response of skin mucous cells in acidexposed fish by migration of the mucous cells towards the epidemial surface combined with increase in cell volume. This could result in an increase in the number of identifiable mu cous cells.…”

“…However, in their study the increase in mucous granules with neutral glycoproteins oc curred after 4 d of exposure whereas the relative decrease in neutral glycoproteins in our study was observed within the first 3 d of exposure. Because mucus is initially synthesised as neu tral glycoproteins (Mittal et al 1980) and the differentiation of new mucous cells takes 5-6 d (Pickering and Macey 1977;Pickering et al 1982;Iger et al 1988), the increase in neutral glycoproteins in the studies of Iger et al (1994) might reflect a differentiation of new mucous cells after depletion of mucous cells in the first phase of exposure. Reid et al (1991) found a reduced gill sialic acid content after 8 d of low pH/Al exposure in rainbow trout.…”

“…A loss in plasma ions in low pH/Al stressed fish is, in the short term, mostly associated with an increase in blood haematocrit (Malte 1986;Audet and Wood 1988;Wood et al 1988). Another prominent characteristic of fish exposed to low pH/Al is the stimulated secretion of mucus (Muniz and Leivestad 1980;Leivestad 1982;Rosseland and Skogheim 1984;Youson and Neville 1987) and the change in chemical composition of mucus on the skin (Zuchelkowski et al 1985;Iger et al 1994) and gills . The role of this mucus secretion and the change in chemical composition of mucus during acid exposure has been suggested to be an adap tive response to prevent osmoregulatory failure (Solanski and Benjamin 1982;Zuchelkowski et al 1985;Jagoe and Haines 1990) or to reduce Al accumulation on the gill epithelium Wilkinson and Campbell 1993).…”

“…Water chemistry (means ± SD, n = 3, temperature = 10.5°C) of the experimental and reference water. reduction in mucous cells due to the exhausted secretion of the mucous cells (Iger et al 1988(Iger et al , 1994. In long-term exposures (over 4 d; Iger et al 1994), the mucification is thought to be due to hyperplasia of mucous cells in skin and gills (Zuchelk owski etal.…”