Fish farms are an environmental reservoir of antibiotic resistance genes (ARGs) due to the treatment of fish with antibiotics that also are important for human medicine. The persistence of ARGs at the farm facilities is a threat to the efficacy of the antibiotics against fish diseases, potentially leading to fish production losses.

Marko Virta group has been done a long-term investigation of the impact of fish farming on ARG compositions and the major sources of ARGs in sediments in the Northern Baltic Sea, Finland every year since 2006. In addition, correlations between ARGs and mobile genetic elements were examined to estimate the potential risk of ARG mobilization in the environment. In collaboration with Prof. Tiedje Lab at Michigan State University, this study employed a high-throughput qPCR array, which permits quantifying hundreds of ARGs and genes associated with mobile genetic elements in a single experiment.

Based on the results of a decade investigations, fish farming impacts the composition of ARGs in sediments below fish farms in the Northern Baltic Sea. However, the impact is local and mostly limited to enrichment of ARGs associated with antibiotics used at the farms. In the current conditions, the risk of ARG spread from the farm sediments to the surrounding sediments is low in the Northern Baltic Sea. Moreover, significant correlations between mobile genetic elements and ARGs may imply the persistence of certain ARGs in the fish farming environments and their potential for mobilizing the ARGs to other bacteria including pathogens.  Our results also provide indirect evidence suggesting that certain ARGs and mobile egentic elements are being constantly introduced by feces of the farmed fish into the sediments below the fish farms.

We are partners in Water-JPI funded project Advanced Biotechnology for Intensive-Freshwater Aquaculture Wastewater Reuse (ABAWARE) which is coordinated by Henning Sørum from Norwegian University of Life Sceinces, Oslo, Norway