Using sterile salmon in aquaculture could mitigate sustainability challenges including precocious male maturation and genetic introgression from farmed escapees to wild populations. By knocking out dead end (dnd) , we have created germ cell-free (GCF), sterile salmon with the potential to remain immature throughout life. We are also developing a method to produce large quantities of GCF salmon. I n this context it is also necessary to characterize the production traits of these fish, and to distinguish the phenotypic effects caused by lacking the dnd gene from effects of lacking germ cells. Being GCF, and hence sterile, is an interesting commercial trait. In this study, we produced GCF and wild type (WT) Atlantic salmon and reared them indoors in a common garden setup with natural light and temperature for 3 years. Fish performance in terms of growth, welfare indictors , gene expression in non-target tissues and fillet quality were evaluated throughout the study . T here were little differences in growth performance between GCF and control early in life. However, condition factor (CF) was lower in GCF at harvest size . Smoltification markers displayed normal levels before and after seawater (SW) transfer for both WT and GCF. P lasma stress indicators including lactate and osmolality concentrations were higher in GCF than WT plasma 24 hours after transfer to SW , but these differences disappeared after 6 months in SW . In adults at harvest size, lactate concentrations were higher in WT than in GCF for both sexes . Transcriptome profiling of muscle and pituitary revealed minuscule differences between WT and GCF in postsmolts after 6 months in seawater . P revalence of vertebra deformities was similar and within a normal range in both WT and GCF fish. No differences were found in hepatic or cardio somatic indexes (HSI/CSI) in postsmolts after 6 months in seawater, however in adults at harvest size, HSI was higher in WT than in GCF fish, while CSI was unaffected. No sexual maturation was detected in GCF fish of either sex throughout the study period, in contrast to their WT counterparts. Fillets from WT and GCF salmon at harvest size showed no significant difference in proximate composition (protein, dry matter or total fat). Interestingly, the relative content of the omega-3 fatty acid DHA 22:6n-3 was higher in GCF compared to WT males despite having the lowest total amount of fatty acids.
GCF fish of both sexes showed lower CF at harvest size, as well as smaller livers, which may reflect altered metabolism in line with the onset of sexual maturation, indicating that nutritional needs may differ between WT and GCF fish. Since GCF individuals were not more prone to develop deformed vertebra than their WT counterparts, GCF farmed salmon may potentially have less problems with quality downgrading losses at harvest with respect to deformities than the currently used triploid sterile salmon. Although the fillet transcriptome and proximate composition did not differ, the finding of increased relative amount of DHA 22:6n-3 in GCF males compared to WT males may represent a more favorable fillet composition for consumers.