University of Guilan Aquatic Physiology and Biotechnology 2345-3966 13 3 2025 12 21 Caspian Sea water tolerance in Rutilus frisii fingerlings through evaluating the osmoregulation capability Caspian Sea water tolerance in Rutilus frisii fingerlings through evaluating the osmoregulation capability 105 121 9486 10.22124/japb.2025.26509.1524 FA Mohammad Sayyadbourani Associate Professor in Inland Waters Aquaculture Research Center, Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Bandar Anzali, Iran Mahmoud Bahmani Professor in Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran Mohaddeseh Ahmadnezhad Assistant Professor in Inland Waters Aquaculture Research Center, Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Bandar Anzali, Iran Adel Hosseinjani M.Sc. in Fisheries, Inland Waters Aquaculture Research Center, Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Bandar Anzali, Iran Mansoor Sharifiyan Associate Professor in Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran Journal Article 2024 01 18 In this study, Caspian kutum fingerlings with 2.5±0.3g body weight were used, which were placed in three treatments, Caspian Sea water with salinity of 11g/L, water with salinity of 7g/L (estuary conditions), and freshwater (river conditions with a salinity of less than 0.5g/L), each group with three replicates. At time intervals of 0, 3, 72, and 240h, blood was taken by cutting the caudal peduncle and blood collected by using heparinized capillary tubes. The concentrations of Mg²⁺, Ca²⁺, Cl^–, Na⁺ and K⁺ ions, osmotic pressure and the level of plasma cortisol hormone were measured. Classical histological method was used to prepare gill tissue sections of the fingerlings. From the results of measuring ions, osmotic pressure and number of chloride cells on the 10th day (240h) of the experiment, it can be confirmed that 2.5g fingerlings were able to regulate their osmolarity in the salinity range of 7 (estuary conditions) to 11g/L (Caspian Sea water). If the estuary conditions are suitable for releasing, kutum 2.5g fingerlings can be used for release into the estuary to maintain the stocks. However, if the river and the estuary conditions are not suitable for releasing kutum fingerling, 2.5 to 3g fingerlings can be released directly into coastal areas (with a salinity of 11g/L). Although, if the river conditions are suitable, releasing the fingerlings in river areas is a necessary condition for the gradual adaptation of them. In this study, Caspian kutum fingerlings with 2.5±0.3g body weight were used, which were placed in three treatments, Caspian Sea water with salinity of 11g/L, water with salinity of 7g/L (estuary conditions), and freshwater (river conditions with a salinity of less than 0.5g/L), each group with three replicates. At time intervals of 0, 3, 72, and 240h, blood was taken by cutting the caudal peduncle and blood collected by using heparinized capillary tubes. The concentrations of Mg²⁺, Ca²⁺, Cl^–, Na⁺ and K⁺ ions, osmotic pressure and the level of plasma cortisol hormone were measured. Classical histological method was used to prepare gill tissue sections of the fingerlings. From the results of measuring ions, osmotic pressure and number of chloride cells on the 10th day (240h) of the experiment, it can be confirmed that 2.5g fingerlings were able to regulate their osmolarity in the salinity range of 7 (estuary conditions) to 11g/L (Caspian Sea water). If the estuary conditions are suitable for releasing, kutum 2.5g fingerlings can be used for release into the estuary to maintain the stocks. However, if the river and the estuary conditions are not suitable for releasing kutum fingerling, 2.5 to 3g fingerlings can be released directly into coastal areas (with a salinity of 11g/L). Although, if the river conditions are suitable, releasing the fingerlings in river areas is a necessary condition for the gradual adaptation of them. https://japb.guilan.ac.ir/article_9486_ccaaac743fc86901dc578564babc0d83.pdf