Seawater tolerance and gene expression in two strains of Atlantic salmon smolts

Abstract

The seawater tolerance of Atlantic salmon (Salmo salar) smolts reared under identical hatchery conditions was assessed in two Norwegian strains: AquaGen and Imsa. Plasma ion levels were disrupted in both strains following seawater exposure, but these disruptions were more profound in the AquaGen fish. To investigate the mechanisms underlying these differences, we measured gill Na+,K+-adenosine triphosphatase (ATPase) activity and mRNA levels of Na+,K+-ATPase α-subunit and two isoforms of the cystic fibrosis transmembrane conductance regulator (CFTR). Gill Na+,K+-ATPase activity rose significantly in both strains following seawater exposure. Both Na+,K+-ATPase α-subunit and CFTR I mRNA levels were significantly elevated for the entire 2-week period following seawater exposure, whereas CFTR II levels were transiently elevated during the first 24 h only. There were no differences in enzyme activity or gene expression between strains, with the exception of CFTR II, which was significantly lower in the Imsa strain 2 weeks following seawater exposure. This suggests that although changes in mRNA and protein expression for these genes are associated with seawater transfer, they are not the basis of observed physiological differences between strains.

Changes in gill H+-ATPase and Na+/K+-ATPase expression and activity during freshwater acclimation of Atlantic salmon (Salmo salar)

“…The deviation in plasma osmolality (~5.4%) from control levels seen in this study during freshwater acclimation was much less than that typically observed during seawater acclimation of Atlantic salmon. Several studies have shown that an increase of ~10-20% is normally seen following seawater exposure (D'Cotta et al, 2000;Singer et al, 2002;Bystriansky et al, 2006). This difference suggests that either osmoregulation is less of a challenge in freshwater or the mechanisms needed to osmoregulate in freshwater can be brought online more quickly during this transition.…”

Differential regulation of cystic fibrosis transmembrane conductance regulator and Na+,K+-ATPase in gills of striped bass, Morone saxatilis: effect of salinity and hormones

“…Primers To amplify striped bass a-subunit Na C ,K CATPase, we used the primers developed by Singer et al (2002), which are based on a conserved portion of the coding region of the a-subunit of several teleosts. Forward primer: 5 0 -GAGATCCTGGCCCGIGATGGCCC-3 0 and reverse: 5 0 -AACCACATGTGGGCCACTGTCAT-3 0 .…”

“…Forward primer: 5 0 -GAGATCCTGGCCCGIGATGGCCC-3 0 and reverse: 5 0 -AACCACATGTGGGCCACTGTCAT-3 0 . To amplify striped bass CFTR, we used the primers developed by Singer et al (2002) specific for the 3 0 -untranslated region (3 0 -UTR) of the Atlantic salmon CFTR-I isoform (Accession no. AF155237).…”

“…Sequence data showed that the present CFTR amplicon is 99% homologue to the Atlantic salmon CFTR-I isoform. PCR was also attempted using primers specific for the Atlantic salmon CFTR-II isoform (developed by Singer et al 2002) but without success. CFTR mRNA levels were unchanged after SW transfer (!96 h), whereas a-NKA a-mRNA increased 6 h after transfer.…”

“…Sodium is secreted passively by a paracellular path, while K C is in electrochemical equilibrium across both apical and basolateral membranes. The role of CFTR in ion secretion by marine teleost chloride cells and its dynamics during salinity transitions have been established in a few teleosts, all of which show increased expression of CFTR in apical membranes in response to SW transfer (killifish: Marshall et al 1999; Atlantic salmon, Salmo salar: Singer et al 2002;Hawaiian goby, Stenogobius hawaiiensis: McCormick et al 2003;eel: Wilson et al 2004; tilapia, Oreochromis mossambicus: Hiroi et al 2005). Apical CFTR-like channels have also been identified in pavement cells of the gill in European sea bass, Dicentrarchus labrax (Duranton et al 1997).…”