Determinig smoltification window of Caspian brown trout through gill Na(+), K(+) -ATPase

To determine the appropriate smolting time of Caspian brown trout (Salmo truttacaspius), gill Na+, K+ -ATPase gene expression were investigated. In this regard,juveniles were randomly sampled in different seasons and then divided into twogroups, either maintained in freshwater or exposed to Caspian sea water (13 ppt) for120 h. Finally, the mRNA expression levels of Na+, K+ -ATPase α subunits (α1a andα1b) and β-actin (as a house keeping gene) were determined in the gills. The resultsrevealed that, in freshwater, mRNA levels of Na+, K+ -ATPase α1a isoform increasedfrom autumn to winter and reached to its highest level in winter, however decreasedagain during spring and summer season. Although there was no significantdifferences among the seasons. Also, a gradual increase was seen in α1b isoformmRNA levels from autumn as fish size progressed and reached to high levels inspring. However, it significantly decreased in summer. α1b isoform of Na+, K+ - ATPase mRNA levels increased in all seasons after transfer to brackish water, whileα1a isoform mRNA levels insignificantly decreased except for autumn. It seems thatCaspian brown trout have the most appropriate physiological conditions for smoltingin spring season.

Keywords:

Na+ , K+ -ATPase subunit , Smolting , Salinity , Caspian brown trout