Marine aggregates in North Atlantic coast: Microbial characteristics and potential interactions with farmed Atlantic salmon (Salmo salar).

Microbial contamination of aggregates collected near an Atlantic salmon farm, in the Cherbourg roadstead, was followed monthly over one year to study the dynamics of Vibrio spp. and explore their impact on farmed fish. Salmon state of health was followed through blood and histopathological analyses. Vibrio were systematically found in aggregates with particularly high concentration in August. The Splendidus clade was strongly dominant in aggregates as well as in gills, and an increase in Vibrio diversity was observed in summer and autumn. Results did not demonstrate that aggregates directly impact the bacterial community of gills, but they suggested an aggregates-gills interaction. Gill contamination was correlated with water temperature and probably impacted by amoebae. Vibrio renipiscarius and Vibrio toranzoniae were isolated in North Atlantic for the first time. A better understanding of the interaction between marine aggregates, Vibrio spp. and fish is essential to improve salmon cage farming.