The trunk kidney of grass carp mainly consisted of renal tubules with a few interstitial
hematopoietic tissues. The component structure of fish nephron markedly varies
between different species of fish. The nephron of grass carp consisted of morphologically
distinct segments; renal corpuscles, neck segment, proximal, intermediate, distal,
and collecting tubules. The glomerulus of renal corpuscles mainly composed of
mesangial cells and well-developed podocytes that extended their processes to the
endothelium of glomerular capillaries forming the filtration barrier. The podocytes
expressed both α-SMA and the transforming growth factor gene, TGF-β. The proximal
convoluted tubules (PCTs) expressed α-SMA iNOS2, and TGF-β. The cytoplasmof PCT
was rich in mitochondria and rER, in addition to the presence of well-developed basolateral
tubular system and apical brush borders. Collecting tubules distributed
throughout the kidney and lined by principal and flask cells. The interstitial hemopoietic
tissues contained iNOS2-positive polymorphic granulocytes, CD3-positive T lymphocytes,
rodlet cells, dendritic cells, macrophages, melanomacrophage centers, and
telocytes. This study described for the first time the cellular components of the nephron
and its associated hemopoietic tissues that can act as a basis for studying the structural
changes that may occur in the kidney of grass carp during water salinitiy,
environmental, or experimental conditions.