Saccular cells in the epidermis of Atlantic cod <i>Gadus morhua</i> L
Infectious diseases are one of the main factors having a negative influence on the Atlantic cod aquaculture. Fish epidermis is a barrier which provides primary interaction between the host and pathogenic organisms. The study of the epidermis of the Atlantic cod Gadus morhua L. has been carried out on the experimental base of the Nord University of Bodo (Norway). Ultrathin sectioning of cod epidermis has been carried out with the help of the Department of Electronic Microscopy of the University of Tromso (Norway). Embryos, pre-larvae from the moment of hatching and larvae up to 3 weeks after hatching, as well as juvenile cod at the age of 5 months, 1 year and 1.5 years have been selected for light-optical and electronic microscope examination. The material for optical studies is fixed with 10 % neutral formalin. The fixation of the material for electronic microscope studies has been made with 25 % glutaraldehyde (sodium cacodylate, pH 7.2). Saccular cells have been found in the cod epidermis of all investigated age groups. The cells have a round or predominantly oval shape and also vacuoles. Vacuoles are filled with an electron-transparent material, but most cells do not have secretory content. It has been found out that secretory material in most cases was absent in the vacuoles of opened cells, where vesicles and tubules, however, remained. During the research, morphological and functional features of these cells are first identified on the basis of studying their distribution, quantity and chemical composition depending on the age of the fish. New data on the spatial distribution of Atlantic cod saccular cells at different stages of ontogenesis have been presented. The results indicate the secretory, bactericidal and protective functions of the saccular cells in the epidermis of Atlantic cod and reflect the ecological features of cod as an epibenthic-pelagic species.