The process of kidney gradual changes in, Tenualosa ilisha during migration from sea to the river

In order to study kidney changes in, Tenualosa ilisha during migration from sea to the river, twenty mature T. ilisha specimens were collected from the Persian Gulf (42.7ppt salinity and 29.27°C temperature) and twenty specimens from Arvand River (2.3ppt salinity and 21.16°C temperature). Macroscopic observation indicated that the kidney was located retroperitoneal and attached to the vertebral column. For histological studies, 5 mm of thickness, from all parts of the kidney removed and fixed in Bouin’s fixative. Routine procedures of preparation of tissues as dehydration, clearing and embedding were followed and paraffin blocks cut at 4-6 micron and stained with Hematoxylin and Eosin. In sea and river specimens, the head of the kidney composed exclusively of hematopoietic tissue. But, in the body and caudal part, the amount of hematopoietic tissue was less and substituted by renal tubules and glomeruli. The microscopic results of kidney tubules showed that nephrons consisted of glomerulus, proximal tubules (I & II), distal tubules and collective tubules. The proximal tubules consisted of cuboidal cells with well- developed brush border. The distal tubules had cuboidal epithelium without brush border. The collecting tubules lined with high cuboidal epithelium. Their nuclei were mainly spherical and located in the central portion of the cells. Morphometric studies showed glomerular volume was larger in fish acclimated to freshwater, and tubules were larger in diameter and had thicker walls (P ≤ 0.05). On this research, we clearly demonstrate that histologic changes take place in the kidney of this marine migratory species that is acclimated to different physicochemical characteristics of sea and freshwater environments.