Acta Biologica Hungarica 45 1 111 121 HUNGARY

Ultrastructural studies were carried out on the nephron of a euryhaline teleost, Oreochromis niloticus. The nephron consisted of a renal corpuscle, neck segment, bisegmental proximal tubule and a distal tubule. Renal corpuscles displayed a trilaminate structure of fenestrated endothelium, triple layered basement membrane and a highly branched podocyte layer. Neck segments consisted of low cuboidal cells with apical cilia and few vacuoles. Proximal tubules were made up columnar cells with apical brush border. The initial part of the proximal tubule (PI) was characterized by a well developed endocytic apparatus which was absent in the next part (PII). Distal segments comprised of low columnar cells with scanty or no microvilli and an extensive system of basolateral membrane infoldings associated with mitochondria. These findings have been discussed in relation to renal function in fresh water euryhaline teleosts