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The study tests the physiological responses of Persian sturgeon, Acipenser persicus, during the abrupt release of juveniles from freshwater ( FW) into brackish waters ( BW = 11‰) of the Caspian Sea. Fish weight at release was 2-3 g (2.55 ± 0.41 g; 8.8 ± 0.58 cm TL). Totals of 160 individuals were randomly distributed into four fiber-glass aerated tanks (volume 60-L). Two tanks served as controls ( FW groups), and two as exposure tanks for BW (Caspian Sea water = CSW). Fish were sampled at 0, 3, 6, 12, 24, 48 and 96 hr after abrupt transfer to CSW. Plasma osmolality, immunolocalization of Na+, K+ - ATPase ( NKA) and Na+/K+/2Cl- ( NKCC) Co-transporter, NKA activity and the NKA α-subunit mRNA expression were analyzed. Blood osmolality of fish transferred from FW to CSW increased significantly within hours post-transfer ( p < .05) and remained at a high level for up to 96 hr. Immunolocalization of NKCC indicated co-localization with NKA in the chloride cells in the gill epithelium. A partial sequence of the NKA α-subunit (632 bp) is described. Its expression levels were up-regulated at 12 and 48 hr following salinity transfer ( p < .05). However, NKA activity sharply increased in CSW specimens by almost 2.8-fold ( p < .05) between 48 and 96 hr after transfer. Gill NKCC co-transporter abundance increased, coinciding with increased gill NKA activity. The increased activity of NKCC during salt excretion in CSW may lead to an influx of Na+ into the chloride cells. Consequently, NKA activity increases to maintain intracellular Na+ homeostasis. [ABSTRACT FROM AUTHOR]

The main objective of this study was to assess genetic comparison of two migratory forms of Caspian trout Salmo trutta caspius namely fall-run and spring-run. Owing to the lack of information on its genetic differences, 5 microsatellite loci were used for 58 sample analyses. Genomic DNA was extracted from caudal fin using Roche DNA extraction kit and each PCR reaction was performed in a 25 µl reaction volume. Results revealed that the most allelic frequencies were observed in fall-runs of Caspian trout. The average observed and expected heterozygosity in fall-runs and spring-runs were 0.7719, 0.6108 and 0.4435, 0.5911, respectively. In both groups except Str543INRA in spring runs, all loci had deviation from HardyWeinberg equilibrium. Furthermore except Str543INRA in spring runs, expected heterozygosity in all loci was more than observed heterozygosity. In conclusion microsatellite loci polymorphism in this study reveals low genetic differentiation between fall-runs and spring-runs. In order to increase gene flow between Caspian trout populations of different rivers and to increase the production of these fishes, restoration of rivers habitats, as well as using more breeders originating from various rivers is highly recommended.