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Abstract The present study has done on 20 pieces L. vannamei shrimp, with average weight 5.53±0.02 g, in 500-liter tanks with three replicates during 8 weeks. At the end, the shrimp intestine were fixed in Bouin's solution for classic histology by Hematoxylin-Eosin (H & E) and green light (GL) and for immunolocalization of the Na+,K+-ATPase enzyme (sodium - potassium pump) by Immunohistochemistry methods. The results showed that the midgut epithelium was covered by simple columnar cells and nucleus position was in basal region of cells and Na+,K+-ATPase enzyme observed in basal region of cells. Evaluation of rectal pad large lobes deep infoldings and distance between the lobes were observed. Lumen was observed in the middle of rectal pad and apical lobes were evident and columnar cells in the marginal infoldings with basal nucleus were observed. Small appendage that called posterior diverticulum was located in primary and in upper region of rectal pad. This region was tubular and it cells with basal nucleus were observed. Rectum was located in distal region of hindgut. This region was a short muscular tube and lined with a simple columnar epithelium with low infoldings and apical nucleus in these cells were observed. The Na+, K+-ATPase enzyme (sodium - potassium pump) was located in baso-latral area in all regions of hindgut cells. We concluded that the use of H&E and GL is an appropriate method to separate different parts of intestine in vannamei shrimp and also immunohistochemistry is a suitable method for Na+,K+-ATPase enzyme localization.

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The ultrastructure of the cells, Na+, K+-ATPase activity and immunolocalization were examined in the barnchial chamber of Libellula lydia (Drury, 1773) larvae. Na+,K+-ATPase activity and localization were performed through biochemical techniques and immunofluorescence light microscopy using a mouse monoclonal antibody IgGα5, respectively. The branchial chamber possesses six pair gills lamellae that extend into the rectal lumen. A thickened epithelial layer and a modified fat body cells layer are present at the base of the each gill lamella. Epithelial cells covered by a thin cuticle and they possess apical microvilli and baso-lateral membrane infoldings associated with mitochondria. The cytoplasm of the modified fat body cells is filled with mitochondria, glycogen and a few lipid droplets. The Na+,K+-ATPase activity was significantly higher (15.36 µM Pi mg-1 protein h-1) in the branchial chamber. Na+,K+-ATPase immunofluorescence staining was observed in the epithelial layer cells of the basal pads of the rectal gill lamellae, with a consistently high immunoreactivity. These findings show that the epithelial cells present cytological features of the ionocytes, a high activity and concentration of Na+,K+-ATPase, confirming their participation in osmoregulation through active ion exchanges.

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In order to determine the effects of fish size and weight on its salinity tolerance, the chloride cells (CCs) immunolocalization changes were examined in Caspian salmon (Salmo trutta caspius) parrs, with the same age (about 2 years old) but different types (type A: 4.88 g, 8.36 cm; type B: 14 g, 11.84 cm; type C: 24.05 g, 14.08 cm). Fish survival rate, blood osmolality, gills CCs histological and immunohistochemical changes were investigated following their transfer from freshwater (FW) to the Caspian Sea water (CSW). The survival rate increased in larger sizes and blood osmolality showed a tendency to increase in parallel with salinity. After 10 days in CSW, some abnormalities were observed in gill structure such as: lamellae cohesion, lamellae rupture and separated lamella from filament epithelium that were shown in all types. These abnormalities in type B were less than the other types. Gill CCs were observed on the gill filament and lamellae. In direct transfer of Salmon parrs to the CSW, changes in number, sectional area, and the surface occupied by CCs in the gill tissue were observed in all the three types. In the type B, the number of CCs did not change, however, in the type C, they decreased, while in the type A, there was significant increase. But in the CSW, the occupied surface by gill CCs in the type C, was reduced significantly compared to other types. According to the present results, among the Salmon parrs with the same age, the fish with type A lacked osmoregulation, while the type B had better compatibility with the CSW. However, after reaching the size of the type C and considering osmultification, it is probable that the type B fish would become compatible with the fresh water environment and they will not have osmoregulation ability in saline water for the long term.