Distribution pattern of branchial chloride cells in smolt Salmo trutta caspius fries of the Caspian Sea during freshwater adaptation

The immunolocalization of Na+,K+-ATPase rich-cells (chloride cells) and their distribution pattern in smolt Salmo trutta caspius fries of the Caspian Sea weighing 5, 15, 25 grams during freshwater adaptation was studied in 2008. Gill samples were fixed in Bouin s solution, and after hydration, the samples were paraffinaized and sectioned. Na+,K+-ATPase localization was performed using IgG 5 antibody and immunohystoshimy technique. In order to count cells in gill area, immunofluorescence light microscopy pictures was analyzed using Image Tool 2.1 software. Chloride cells were found on gill arch, lamellae and filament. Filamentary chloride cells and their total number (chloride cells in lamellae and filament) had no significant difference in all 5, 15, 25g specimens but lamellar chloride cells in 5g fries was significantly decreased. Also, percentage of lamellae chloride cells in 15g specimens and those of filament chloride cells in 5g fries was higher than other weights. According to our results, weight has important impact on osmoregulation ability in same age fishes. Fries with higher weight can resist salinity stress after migration to Caspian Sea through production of more chloride cells and change in their position but those which remain in freshwater for a long time, would adapt easily to the new environment.