Norwegian researchers identify "death algae" toxin responsible for recent fish mortalities

Researchers at the Norwegian Veterinary Institute (Veterinærinstituttet) have identified the algal toxin that has caused fish mortalities at salmon farming sites in northern Norway this spring, after a harmful algal bloom struck Nordland and Troms.

The bloom has killed an estimated one million farmed salmon, including 250,000 smolts, according to the Norwegian Directorate of Fisheries.

Following advanced chemical analysis of water samples from the affected fish farms, researchers established that the culprit is leadbeaterin-1, a substance which is lethal to fish and present in the so-called "death algae" species Chrysochromulina leadbeateri.

This is the same toxin that killed millions of salmon in 2019, when over seven million farmed salmon died in Northern Norway during a major harmful algal bloom, researchers say.

The Institute announced last October it had made a breakthrough in identifying the algal toxin from 2019, demonstrating that leadbeaterin-1 was the likely reason behind the gill damage and fish deaths seen during the harmful algal bloom.

"The fact that we have identified the toxin and developed a method for detecting the algal toxin in water samples provides opportunities for the development of better methods for monitoring and early detection," said researcher Ingunn Anita Samdal at the Norwegian Veterinary Institute, in a press release.

"With more research, it will also be possible to develop faster methodologies for detecting the toxin outside the facilities," she added.

The Veterinary Institute says that the algae C. leadbeateri was detected in the same area where the fish mortalities occurred in recent weeks, and was also found by Norway's Institute of Marine Research in one of its water samples.

The toxin was identified through the ongoing collaborative research project ToxANoWa, funded by the Research Council of Norway. Led by the Norwegian Veterinary Institute, ToxANoWa includes collaboration between the University of Oslo, the Technical University of Denmark and the National Research Council of Canada.

The Veterinary Institute is also collaborating with the company Sea Eco in Harstad to collect more water samples, and said it hopes to develop this further in collaboration with the industry.