AppearanceTrends of Gilland SkinIonocytes InThe Early Larval Development of ZanderSander lucioperca

Inroduction & Zander, Sander lucioperca, is an economical fish in the Caspian Sea. Due to the decline of stock in recent years, fry with different weights are released into the rivers by Iran Fisheries Organization. Studyonosmoregulatory function especially in developmental stages of larvae is essentialtorefinethe process offish into thefreshwaterorsaltwaterenvironments. Development of gill osmoregulatory Function, distribution and density of skin ionocytes were examined by histology with E & H staining and immunolocalization of Na, K-ATPase, in Caspian Sea zander (Sander lucioperca) larvae from day 1 to day 11 after hatching. Development of filaments was started from 4th days but immunopositive ionocytes were not observed in them. It was found weak immunofluorescence in filaments on the 8th days. The first buds of lamella were appeared with very poor immunofluorescence on the 11th days. Predominant distribution of the skin ionocytes was limited to the yolk sac membrane to 8 days after hatching and then tended to ventral region of posterior end of body. Skin ionocytes abundance and surface occupied by them increased from the first day to 11 days after hatching. In Caspian Sea zander larvae, development of osmoregulatory function of the gill had not been complete up to the 11th days and the skin ionocytes were responsible for osmoregulation until this age.