Comparison of bacterial diversity and distribution on the gills of Atlantic salmon ( Salmo salar L.): an evaluation of sampling techniques

Assess bacterial diversity and richness in mucus samples from the gills of Atlantic salmon in comparison to preserved or fixed gill filament tissues. Ascertain whether bacterial diversity and richness are homogeneous upon different arches of the gill basket. Bacterial communities contained within gill mucus were profiled using 16S rRNA gene sequencing. No significant difference in taxa richness, alpha (P > 0·05) or beta diversity indices (P > 0·05) were found between the bacterial communities of RNAlater preserved gill tissues and swab‐bound mucus. A trend of lower richness and diversity indices were observed in bacterial communities from posterior hemibranchs. Non‐lethal swab sampling of gill mucus provides a robust representation of bacterial communities externally upon the gills. Bacterial communities from the fourth arch appeared to be the least representative overall. The external mucosal barriers of teleost fish (e.g. gill surface) play a vital role as a primary defence line against infection. While research effort on the role of microbial communities on health and immunity of aquaculture species continues, the collection and sampling processes to obtain these data require evaluation so methodologies are consistently applied across future studies that aim to evaluate the composition of branchial microbiomes.