Potential role of Mytilus edulis in modulating the infectious pressure of Vibrio anguillarum 02β on an integrated multi-trophic aquaculture farm

Marine finfish producers in the Northeast are adopting an integrated multi-trophic aquaculture (IMTA) approach by growing mussels, Mytilus edulis, with marine finfish species. Shellfish play a critical role in an IMTA system by filtering particulate bound nutrients and other seston from surrounding waters. During feeding, mussels bio-accumulate microbes, including fish pathogens, from the water column. This may influence pathogen dynamics on IMTA farms by either reducing infectious pressure or by serving as a reservoir for important finfish pathogens. The first step in evaluating the disease risks or benefits on a mussel-fish IMTA farm is to understand the interaction between mussels and finfish pathogens. We investigated the fate of the cod bacterial pathogen Vibrio anguillarum 02β in the blue mussel Mytilus edulis. Mussels exposed to 104 CFU of V. anguillarum ml− 1 concentrated bacteria in digestive gland tissues 2 orders of magnitude above the concentration of bacteria in the surrounding water. To determine if mussels could release concentrated bacteria back into the environment, V. anguillarum-exposed mussels were transferred to clean water and fecal and water samples were analyzed for the presence of bacteria. V. anguillarum was not detected in the water; however mussel feces and pseudofeces had high loads of V. anguillarum (107 CFU g− 1). Within 72 h of depuration, V. anguillarum was no longer detected in fecal samples. Immersion challenge trials using fecal material from V. anguillarum-exposed mussels resulted in 58–70% mortalities in challenged cod. These results demonstrate that mussels are capable of bio-accumulating V. anguillarum and shedding virulent bacteria through their feces. While this study does not likely reproduce the dynamic conditions on a finfish–mussel farm, results obtained do present valuable information when considering biosecurity and pathogen risk reduction on IMTA farms.

► Mussels concentrate Vibrio anguillarum in tissues 2 orders of magnitude above levels in the water.
► Vibrio-loaded mussels release high levels of viable V. anguillarum in their feces.
► Atlantic cod exposed to Vibrio-loaded mussel feces suffer mortalities as high as 70 %.
► Mussels may influence infectious pressure on integrated multi-trophic aquaculture farms.