When spring comes, the young salmon parr has to prepare migrating to a completely new environment, from the bottom of freshwater bodies to open sea, in a process called smoltification. It has been shown that light (duration of the day) and salt (change in salinity) induce drastic changes in the body of the parr, including in the outer pigmentation, the general metabolism, and specific changes at the level of the brain and the gills.
These changes involve endocrine activity, in particular thyroid hormone signaling. The project team, through a wide international collaboration, has shown that the expression of the two thyroid hormone deiodinase type 2 paralogues (a and b) is increasing in response to light and salt, in areas know to be remodeled during smoltification.
Read more about the project - http://uni.no/en/news/2015/04/30/how-mixing-light-salt-makes-smolt/