The Vascularization of the Kidney of the Eel (Anguilla anguilla - Osteichthyes) in the Freshwater Habitat

The renal vascular system of eels (Anguilla anguilla L.) in freshwater has been investigated using light-, transmission electron-, and scanning electron microscopy of vascular corrosion casts and critical-point dried specimens. The morphology of the kidney exhibits a highly evolved, unpaired, spindle-shaped form. The renal tissue extends partially into a recessus dorso-caudal to the anus. Renal glomeruli are comparatively large (100.8 μm +/-17 standard deviation) and well vascularized. They are arranged in grape-like clusters around the intrarenal arteries. Closely neighbouring glomeruli can be surrounded by incompletely separated Bowman\u27s capsules sharing the same renal tubule. The peritubular capillary plexus is mainly supplied from the right posterior cardinal vein (renal portal vein) and is relatively dense (about 30 vol.% - measured from corrosion casts). Conspicuous vascular patterns consisting of a central vein and, at a distance of about 25 μm, a peripheral meshwork of arterioles are frequently found. The nature and function of these structures, however, remains to be studied