Temporal changes in skin and gill microbiomes of Atlantic salmon in a recirculating aquaculture system – Why do they matter?

Mucosal surfaces are key components of teleost health, providing defence against opportunistic pathogens and other insults. Maintaining the integrity mucosal their associated microbial communities, especially gill skin that have large surface areas exposed to environment is essential. Production Atlantic salmon in land-based recirculating aquaculture systems (RAS) has increased significantly recent years as it allows greater control over stability which fish reared, reduces water demand minimises environmental impacts. However, little known about impact RAS upon temporal dynamics microbiomes. In this study we examined communities mucus, mucus rearing throughout freshwater (FW) production, at 1-week 4-weeks following transfer seawater (SW) open cage production using 16S rRNA sequencing. Microbial diversity richness reared a system were temporally dynamic. Dynamics similar two tissues, some extent also mirrored surrounding water. Dysbiosis indicated by an abrupt decline during FW coincided with increase relative abundance taxa belonging RAS-biofilter-associated nitrogen-cycling genus Hydrogenophaga tank was observed mucus. Extensive overlap core between but host-specific cores non-existent dysbiotic event all present Diversity remained stable transition from SW, distinct community composition environments. Although closely controlled, significant variation could be temperature well levels CO2 nitrogen compounds, reflecting increasing biological load within time. The results presented here suggest that, terms microbiomes, dysbiosis may occur both time, capability recover.