Novel method for quantifying salmonid mucous cells

The primary defence mechanism of fish exposed to an infectious or damaging agent is the physical barrier of skin, gills and gastrointestinal tract and their protection mechanisms associated with the innate immune defence system, the mucosal epithelium. Mucus production helps to protect these physical barriers by acting as a diffusion barrier and lubricant whose function is to protect the epithelial cells from infection, dehydration and physical or chemical injury. Mucus also contains several bioactive components such as immunoglobulin, complement C-reactive protein, lectins, lysozyme, proteolytic enzymes, alkaline phosphatase and esterase, antimicrobial peptides and haemolysin, which exhibit biostatic or biocidal activities (Alverez-Pellitero 2008). Recent work has shown that mucus secretion, in the gut and on the skin of fish, may be augmented by nutritional components and this can affect bioactive components and barrier defence mechanisms associated with Vibrio infections in sea bass and sea lice infections in juvenile salmon (Sweetman, Torrecilla, Dimitroglou, Rider, Davies & Izquierdo 2010; Torrecillas, Makol, Benitez-Santana, Caballero, Montero, Sweetman & Izquierdo 2011). The determination, therefore, of a quantitative method to assess the distribution, abundance and volume of goblet cells in various strategic locations on the Atlantic salmon, Salmo salar L., would provide a new tool for the further evaluation of mucosal interactions and fish health. This paper describes a novel stereology-based method for quantification of the skin components and mucous cells of salmonids. Fish skin is highly metabolically active and acts as a multipurpose primary defence mechanism against aquatic pathogens and parasites (Rakers, Gebert, Uppalapati, Meyer, Maderson, Sell, Kruse & Paus 2010). Fish skin contains the outer epidermis and inner dermis, transdermal scales and mucous cells. The epidermis can be further divided into the stratum superficiale where the squamous epithelial cells mix with a population of mucous cells; the stratum spinosum with some differentiated cells; and the stratum basale with basal cells and a basement membrane. Undifferentiated cells migrate from the stratum basale to the stratum spinosum and then recruit when necessary to the stratum superficiale. The epidermis is separated from the dermis by the basement membrane with filamentous proteins. The dermis has a stratum laxum and a stratum Journal of Fish Diseases 2011, 34, 931–936 doi:10.1111/j.1365-2761.2011.01308.x