Mature nitrifying biofilters counteract invasion by rapid-growing heterotrophic bacteria in recirculating aquaculture systems (RAS)

Nitrifying biofilters are essential components of recirculating aquaculture systems (RAS) for nitrification. Beyond this primary function, their role in shaping the microbial environment for fish remains underappreciated. We previously hypothesized that mature biofilters would resist bacterial invasions and suppress the proliferation of rapid-growing heterotrophic bacteria. We performed two experiments to test this hypothesis: first, in small-scale RAS with Atlantic salmon ( Salmo salar ) fry, a