An important phase in the Atlantic salmon life cycle is the smoltification process, which prepares the fish for the parr-smolt transformation. This process is a complex adaptation that consists of several molecular drivers. For instance, in the gills, cortisol and the GH / IGF-1 axis promote the up-regulation of sodium-potassium-ATPase (NaK-ATPase). The NaK-ATPase activity is used in the salmon aquaculture as a smoltification marker, and RT-qPCR for this gene has recently been implemented. However, the NaK-ATPase levels can strongly be altered by hatchery conditions.
This study aimed to explore the putative role of microRNAs during the seawater transfer (SW), and identify novel biomarkers based on non-coding RNAs. For this, Atlantic salmon smolts were exposed to gradual salinity change, and gills samples were used for miRNAs mining by Illumina sequencing. A panel of miRNAs with significant expression changes during the SW transfer were validated through qPCR analysis. For the validation, gills samples were obtained during four weeks before the SW transfer. In addition, NaK-ATPase enzymatic activity was evaluated to corroborate the smolt condition.
Herein, we present six biomarkers candidates to evaluated the smolts conditions by qPCR. A significant NaK-ATPase enzymatic activity levels increase was recorded. Moreover, qPCR analysis showed a significant gradual increase of miR-128, miR-23a-3-5p, and miR-205a-5p during the sampling weeks. On the other hand, miR-205, miR-21a-2-3p, and miR-222 showed a progressive down-regulation during the smoltification (Fig. 1). In addition, the target gene analysis evidenced that ATPase-α subunit and can be regulated by miR-21a-2-3p (Table 1). These findings support novel biomarkers for smoltification in salmon aquaculture.
Funding: ANID-Chile through the Postdoctoral grant FONDECYT (#3190320), and FONDAP (#15110027).