ABSTRACT
Closed production systems with control of the light regime and water temperature enables the time of smoltification to be controlled to a much greater extent than in traditional open systems with natural daylight and temperature cycles. This opens the possibility for flexible production, nearly independent of season and depending on the possibility for receiving the fish in the ongrowing unit. By simulating natural changes in light, normal parr-smolt transformation can be induced. Normal light levels and light colours have no major effect on the process. An apparently normal smoltification of salmonids raised under continuous light, can also be achieved by employing a short-day regime of minimum five weeks, followed by continuous light. Long-term survival and growth in sea water of smolts raised under artificial light regimes are similar to those of smolts produced under natural light. Further development is necessary to implement this method in full-scale production.
