CONFOCAL LASER-SCANNING AND ELECTRON-MICROSCOPIC STUDIES ON OSMOREGULATORY EPITHELIA IN THE BRANCHIAL CAVITY OF THE LOBSTER HOMARUS-GAMMARUS

The adult lobster Homaras gammarus is a weak hyper-regulator at low sa linity. The objective of this study was to locate the ion-transporting tissues in the branchial chamber of this species, using electron micr oscopy and confocal laser scanning microscopy with a fluorescent vital stain for mitochondria, DASPMI, which is widely used to locate mitoch ondria-rich cells in ion-transporting epithelia of fish. A thick mitoc hondria-rich epithelium is present on the inner side of the branchiost egite and over the entire surface of the epipodites, Ultrastructural o bservations confirm that this tissue has features typical of an ion-tr ansporting epithelium. When the lobster is transferred to low salinity , these epithelia undergo marked ultrastructural changes, such as an i ncrease in thickness related to the development of basolateral infoldi ngs, the appearance of numerous vesicles and an increase in height of the apical microvilli, In the gills, the branchial filaments are lined by a thin and poorly differentiated epithelium, containing numerous m itochondria; no significant ultrastructural changes were observed in t he gills of animals acclimated to low salinity. In summary, in H, gamm arus, no evidence of osmoregulatory structures was found in the gills. Differentiated ion-transporting epithelia are present in the branchia l cavity, on the inner side of the branchiostegite and on the epipodit es; these organs are probably involved in osmoregulation.