Photoperiod in recirculation aquaculture systems and timing of seawater transfer affect seawater growth performance of Atlantic salmon ( <i>Salmo salar</i> )

Production of Atlantic salmon smolts in recirculation aquaculture systems (RAS) is growing, and novel production protocols using continuous light RAS are being implemented the industry. In present study, Salmon parr were exposed to either a traditional protocol (short-day winter signal [12:12 L:D] for 6 weeks) or light. Both photoperiods applied freshwater (FW) brackish water RAS. from all treatments transferred seawater pens at 200 600 g grown until slaughter size. A control group was smoltified with 6-week short-day kept FW sea transfer 100 g. Continuous gave higher growth rate but reduced feed intake increased conversion ratio during first 8 weeks seawater. However, slaughter, fish bigger than given because Slaughter weight lowest g, despite having highest day-degree sum their life span. The best performing All handled survival maturation not affected by immune status examined multigene expression assay on BioMark HD platform stage 5–7 months after transfer. Overall, there no significant effect photoperiod salinity selected genes. sum, results this study indicate that may have negative effects performance shortly whereas had irrespective treatment