Adaptation of a fluorocarbon-based non-aqueous fixation regime for the ultrastructural study of the teleost epithelial mucous coat

Studies on the microanatomy of the mucus-rich biofilm surface of normal or damaged teleost skin tissue have been limited because conventional fixation regimes do not effectively retain mucus during tissue preparation. A non-aqueous fixation method, based on a technique devised to retain airway mucous for ultrastructural study, and consisting of the use of an inert perfluorocarbon solvent with osmium teroxide 1%, was successfully used to prepare skin tissues of healthy juvenile rainbow trout. The skin's mucous coat was examined by transmission electron microscopy and the results were compared with those obtained with tissues prepared by a conventional glutaraldehyde-based method. In samples fixed with glutaraldehyde, the cell-surface structures retained were limited to microridges and a poorly discernible glycocalyx layer. In contrast, those fixed by the non-aqueous method had a more clearly demonstrated glycocalyx layer, and a second fibrillar layer, resembling mucus, which was separated from the glycocalyx layer by an electron-lucent zone.