Land-based fish farms may become reservoirs for Tenacibaculum
'As land-based salmon farming expands, our results emphasise the importance of systematic monitoring and implementation of biosecurity strategies to prevent persistence and reinfection of pathogens in biofilms in the facility infrastructure,' warn researchers
A new study from the University of Bergen highlights that land-based salmon production can not only reduce infection pressure from the sea phase, but that the same structures that provide better control over water, the environment and production can also provide a foothold for biofilms with pathogenic bacteria.
In the study, the researchers found a clear shift from Tenacibaculum maritimum in September, to T. dicentrarchi which was mainly isolated in December.
The finding of T. maritimum in Atlantic salmon in Norway was also the first documented evidence that this bacterium infects Atlantic salmon in Norway.
Control on the water is not the same as control on the surfaces
The researchers show in the scientific article that a land-based facility is not necessarily biologically closed, even if it is technologically controlled, and that control of the water is not the same as control of the surfaces.
They point out that land-based facilities offer large internal surfaces – pipes, vessel walls, drains and other structures – that can facilitate fouling and bacterial persistence. Thus, the infrastructure itself can become an environment where fish pathogenic bacteria survive, establish biofilms and, in the worst case, act as a source of reinfection.
In this study, both fish and environmental samples were examined in a Norwegian land-based facility from September to December 2024. It revealed a marked shift in the bacterial flora: T. maritimum dominated in September and was linked to mortality during an ulcerative disease outbreak, while T. dicentrarchi was mainly isolated in December – both from wounds on fish and from structural elements in the facility.
Transmission routes can therefore be built into the production environment itself.
Changed risk picture
The researchers also point out that recurring summer heat waves in Norway, in connection with global warming, may provide T. maritimum with better conditions.
The fact that T. maritimum is now documented in Atlantic salmon in Norway for the first time is therefore more than just a species registration. It points to a possible changed risk picture in that if biosecurity and cleaning regimes are not sufficiently targeted, this may create new niches for persistence.
Land-based growth requires more systematic monitoring
In conclusion, the message is clear: as land-based salmon farming grows, so does the need for systematic monitoring and biosecurity strategies that are adapted to biofilm-associated pathogens.
The researchers point out that such bacteria can use the infrastructure as a reservoir, and that this must be taken into account in risk assessments, cleaning design, sampling routines and daily operations.
