[Gill structure in healthy carp]

When the gills of carp are studied, this organ should be evaluated from there planes of projection: sagittal, transversal and horizontal. Lamellae, the functional base of the gills, provide the exchange of oxygen between blood and water. Lamellae consist of a network of sinuses with a skeleton formed by columnar cells and with walls constituted by the cytoplasmic processes of these cells. On the outer side the sinuses are covered with one or two layers of flat epithelial cells. The gill filaments and gill arches, the structure and mobility of which enable the perfect function of lamellae are covered with stratified epithelium. Cylindrical cells (germ cells) of this epithelium are borne by a basal membrane; during maturation they flatten and differentiate towards the surface. Besides the already flat epithelial cells, the surface of epithelium also carries mucous cells and gustatory buds. Separate large irregular cells with excentric nucleus and small eosinophilically staining granules are also found in the epithelial layers of healthy fish.