Deadly algal bloom killed 7 million fish—now we know why.
Researchers from the Veterinary Institute of Norway, along with international collaborators, have identified the toxin responsible for the 2019 mass mortality event, where over seven million farmed salmon died during a severe algal bloom in northern Norway.
The algae Chrysochromulina leadbeateri was found to have produced a previously unknown family of toxic compounds, named leadbeaterins, which are believed to have caused gill damage in the fish. The discovery is part of the ToxANoWa project, which aims to better understand the harmful effects of toxic algae on aquaculture.
The algal bloom, which also occurred in 1991, 1998, and 2008, led to significant losses for Norway’s aquaculture industry. Researchers cultivated large cultures of the algae to identify the chemical compound responsible. Ingunn Anita Samdal, project leader at the Veterinary Institute, confirmed that the leadbeaterins, similar to previously known karlotoxins, were toxic to fish gill cells, potentially causing the widespread mortality observed in 2019.
The study has yet to determine the exact mechanisms by which the toxins damage gills or the specific algae concentration levels needed to trigger the fatal effects. The project also analyzed water samples from the 2019 bloom and confirmed the presence of the toxins in samples from Troms, solidifying the link between the bloom and the fish deaths.
Samdal explained that while the discovery is a critical step, further research is needed to fully understand the risks posed by such algal blooms and to better protect the aquaculture industry from future events. Findings were presented at the Havbruk 2024 conference, showcasing the ongoing international collaboration to address this issue.
The project, which includes the University of Oslo, Denmark’s Technical University, and the National Research Council of Canada, is supported by the Norwegian Research Council.
