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 inflammatory processes was studied by electron microscopy. Macrophages and neutrophils appeared extensively infiltrated between the detached malpighian cells. The neutrophils can be identified by a multilobed nucleus, sometimes having thin sheets of chromatin. There are three types of cytoplasmic granules: fibrillar, with homogeneous contents, and with striated inclusions. Numerous, isolated, flattened vesicles are scattered in the cytoplasm; they present characteristic forms: curved, horseshoe-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 seen, unlike it happens in the neighbouring epidermal macrophages. Starting from the presence of melanin, other functions of these tissular neutrophils related with defence mechanisms are discussed.