A bacterial and viral genome catalogue from Atlantic salmon highlights diverse gut microbiome compositions at pre- and post-smolt life stages.

Resolving the microbiome of the Atlantic salmon Salmo salar gut is challenged by a low microbial diversity often dominated by one or two species of bacteria, and high levels of host contamination in sequencing data. Nevertheless, existing metabarcoding and metagenomic studies consistently resolve a putative beneficial Mycoplasma species as the most abundant organism in gut samples. The remaining microbiome is heavily influenced by factors such as developmental stage and water salinity.