Smoltification (also known as Parr-Smolt transformation) is the series of physiological changes where juvenile salmonid fish adapt from living in fresh water to living in seawater. Physiological changes during smoltification include altered body shape, increased skin reflectance (silvery colouration), and increased Na+/K+-ATPase in the gills. A number of mechanisms assist with osmoregulation.
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Smoltification Wikipedia(Text) CC BY-SA