Spawning manipulation, broodfish diet feeding and egg production in farmed Atlantic salmon

Atlantic salmon aquaculture relies on continuous supply of high quality eggs. Broodfish nutrition and manipulation of ovulation time (photoperiod and temperature) are key factors. The optimum feeding period with broodfish diet has not been investigated before. The present study examined how feeding period with broodfish diet (9 vs. 17 months) interacted with manipulation of ovulation time (early (Nov), normal (Dec), late (Feb)) on broodstock egg production capacity and egg quality in two-sea-winter female Atlantic salmon (similar to 12 kg). All groups were fed until June 2021 when they were transferred to tanks and starved until ovulation.There were no measurable main or interaction effects of feeding period. Manipulation of ovulation gave several significant effects compared to normal ovulating females: 1. Early ovulating females had higher viscerosomatic index, smaller eggs with higher swelling rate (early 1.36, normal 1.27, late 1.23), and lower egg quality shown as reduced survival from fertilization to the eyed egg stage (mortality: early 11%, normal 5%, late 14%). 2.Late ovulating females: ( i ) were emaciated as shown by low condition factor calculated on gutted weight, and hepatosomatic and viscera indexes; ( ii ) had larger gonads caused by larger eggs; ( iii ) had reduced egg quality measured as elevated mortality from fertilization to first-feeding (eyed egg - first feeding: early 11%, normal 8%, late 23%). 3. All groups spawned a similar number of eggs per female. The current results show that the feeding period with broodstock diet may be set to 9 months. This would make Atlantic salmon egg production more economical and environmentally sustainable. The results also show that manipulation of ovulation time reduce egg quality but not fecundity. Further research should investigate feeding periods with broodstock diet shorter than 9 months and determine the threshold for jeopardized fish welfare with respect to starvation time for manipulated late ovulating females.