The aim of WP1 is to set up a photoperiod manipulation experiment at the Akvaplan-niva facilities in Tromsø, Norway. Full-sibling Atlantic cod individuals are carefully selected from the National Cod Breeding Program (NCBP), a unique resource for fundamental research in Atlantic cod. The experimental design includes 6 tanks, three of which will simulate natural photoperiod conditions in Tromsø, and the other three tanks continuous light (24L:0D).