Association between melanin deposits in gill tissue and microbiome across different hatchery reared Atlantic salmon.

This study investigates the relationship between gill microbial communities and gill pathology in Atlantic salmon across a production cycle in two commercial freshwater hatcheries with differing water sources and rearing systems: one combining recirculation aquaculture system (RAS) and flowthrough (FT) using riverine water, and the other using bore water with continuous RAS. Using 16S rDNA amplicon sequencing alongside histopathology and water quality data, the researchers found that melanin deposits in gill tissues were prevalent in early life stages and correlated with distinct shifts in bacterial community composition, including higher abundances of genera such as Sphaerotilus, Pseudomonas, and Nitrospira. The study also observed that bacterial diversity increased when fish transitioned from RAS to FT systems, and that hyperplastic and inflammatory lesions correlated with specific bacterial taxa rather than overall diversity changes. These findings suggest a link between the commensal gill microbiome and gill health status under commercial aquaculture conditions, highlighting the potential role of microbial community dynamics in gill pathology development.