A sharp decrease to −2 of epidermis was observed in the skin of Atlantic salmon Salmo salar at the beginning of the smoltification period in 1997 and 1999. Average numbers decreased in 1997 from 662 mm −2 on 6 March to 275 mm −2 on 20 March and in 1999 from 828 mm −2 on 3 March to 388 mm 2 on 24 March. A second smaller decrease was observed towards the end of smoltification in both years.