Defence-relevant gene expression differences in hatchlings among wild Newfoundland and farmed European and North American Atlantic salmon and their hybrids.

Escape of genetically distinct farmed Atlantic salmon (Salmo salar) raises concerns about their potential interactions with wild populations and the disruption of local adaptation through genetic admixture. It is often unknown whether genetic origin or common domestication effects will have a greater influence on consequences posed by escaped farmed fish. Previous work showed that domestication could have prevalent effects on the behaviour and growth of farmed salmon, independent of their genetic origin. Yet, less is known whether this extends more broadly to gene expression, particularly at critical early life stages. Thus, we compared the expression of 24 transcripts related to the immune response, structural maintenance, stress response and iron metabolism among distinct farmed (North American [NA] and European [EO]), wild (Newfoundland) and F₁ hybrid salmon at hatching under controlled conditions using qPCR analyses. A slightly higher number of transcripts were differentially expressed between the wild population relative to EO (i.e. atf3a, atf3b, bnip3, trim37a, ftm, hp and gapdh) than NA-farmed salmon (i.e. epdl2, hba1a, hba1b, hbb4 and ftm). The most differences existed between the two farmed strains themselves (11 of 24 transcripts), with the fewest differentially expressed transcripts found between the F₁ hybrids and the domesticated/wild maternal strains (4 of 24 transcripts). Interestingly, despite similarities in the overall extent of gene expression differences among cross types, the expression patterns differed relative to a past study that compared fry from the same cross types at the end of yolk sac absorption. Overall, our findings suggest that interbreeding of escaped farmed salmon with wild Newfoundland populations would alter transcript expression levels and that developmental stage influences these changes.