NEUTROPHIL GRANULOCYTES IN THE EPIDERMIS OF THE BROWN-TROUT, SALMO-TRUTTA L - ULTRASTRUCTURAL CHARACTERIZATION

Epidermis of the brown trout, Salmo trutta L., displaying signs of inf lammatory processes was studied by electron microscopy. Macrophages an d neutrophils appeared extensively infiltrated between the detached ma lpighian cells. The neutrophils can be identified by a multilobed nucl eus, sometimes having thin sheets of chromatin. There are three types of cytoplasmic granules: fibrillar, with homogeneous contents, and wit h striated inclusions. Numerous, isolated, flattened vesicles are scat tered in the cytoplasm; they present characteristic forms: curved, hor seshoe-shaped or thoroidal. Melanin granules can be also found in the cytoplasm, but whether their origin is phagocytic or autophagic is not clear. Evidence of the phagocytic ability of the neutrophils is not s een, unlike it happens in the neighbouring epidermal macrophages. Star ting from the presence of melanin, other functions of these tissular n eutrophils related with defence mechanisms are discussed.