Preliminary ultrastructural studies of the surface mucus of Atlantic salmon

The ultrastructure of healthy skin mucus of Salmo salar was examined and the possible changes induced by infestation with Lepeophtheirus salmonis investigated. Until recently, there have been no methods for reliable preservation of fish skin mucus. A fixation method that uses a non-aqueous solvent and osmium tetroxide was developed for this purpose. Results indicate that the surface mucus of Atlantic salmon is multilayered. Mucus cells probably contribute most of an outer, dense layer, while other epithelial cells probably secrete materials into a lower lucent zone between the epidermal ridges. When compared with non-infested fish, Atlantic salmon with moderate to severe infestation of sea lice have significantly thinned or "washed out" mucus..