Groups of Atlantic salmon ( Salmo salar) parr were reared under indoor light sources of different spectral composition. A control group was reared under outdoor light conditions. Growth rate was not significantly different among the indoor groups, whereas the outdoor group had a significantly lower growth rate. All groups developed the external appearance and experienced the reduced condition factor and increased salinity tolerance normally associated with the parr-smolt transformation. Fish from all groups were successfully acclimated to seawater in early May. The subsequent 6-month growth period in seawater did not reveal any differences in growth potential of fish from the different experimental groups. It was concluded that the parr-smolt transformation was completed under light sources of different spectral composition.