study of structural evolution and its role in osmotic regulation during early development of the Caspian Sea salmon, Salmo trutta caspius

Salmo trutta caspius is a euryhaline fish that tolerate salinity fluctuations during the maturation process with a number of morphological and functional adaptation. There is little information about kidney of this native Caspian species that play an important role in ion balance in body fluids is information exists. In the present study ontogeny (development process) of renal system (kidney and urinary bags) in terms of structure and function in osmotic regulation from first day post hatching to 27 days through histology and immunohistochemistry were studied. Results showed that on the first day post hatching, proneprosic kidney was located along the body and digestive tract. Until the sixth day, Poximal tubules showed low complexity but in next days they showed differentiation and increased in number and complexity. mesonephric tubules appeared with dark cell mass on sixth day. Glomeruli was seen on days 12 after hatching and was characterized by mesonephric and blood cells and Bowman capsule. Between days 16 to 22 number of mesonephric tubules was increased, so that blood tissue between them decreased and all the the renal tissue was embedded by tubules. After that formation of mesonephric kidney with decreased blood tissue and Pronephric tubules was observed. Imunolocalization of Na+ / K+ ATPase in one-day larvae was seen strongly in many parts, means that lots of this enzyme is available in basal membrane. By growing larvae, immunofluorescence intensity in different parts of the kidney showed significant changes. It could be concluded¬ until formation of Mesonephric kidney, the main role in osmotic regulation is played by Pronephric tubules but later this role is transferred to mesonephric tubules.