GILL EPITHELIAL-CELLS KINETICS IN A FRESH-WATER TELEOST, ONCORHYNCHUS-MYKISS DURING ADAPTATION TO ION-POOR WATER AND HORMONAL TREATMENTS

The aim of this work was to determine the kinetics of the dramatic dev elopment of the gill chloride cells (CCs) during adaptation of the sal monid Oncorhynchus mykiss to an ion-poor environment. To monitor cell division, the incorporation in the mitotic cell DNA of bromo-deoxyurid ine (BrdUrd) was visualized with a monoclonal antibody. The density of labelled nuclei was used as an index of cellular division (proliferat ion), concomitantly with morphometry of phenotypic changes monitored w ith SEM. In the filament epithelium, a phase of CC differentiation occ urred within 12h after the transfer, followed by a delayed phase of ce ll proliferation (48h). In the lamellar epithelium, the present study demonstrates the absence of cell proliferation after ion-poor water tr ansfer. The conclusion is that proliferation (mitosis) is important in the primary filament whereas differentiation and migration (from the filament) is the main mechanism for the appearance of CCs on the secon dary lamellae. The present study suggests that cortisol promoted diffe rentiation, but not division, of cells. CCs, presumably premature, wer e stained by anti-cortisol monoclonal antibody indicating the presence of cortisol. No mature CCs were stained. Growth hormone (oGH, ratGH) increased the rate of cell division both in lamellar and filament epit helium.