Oslo-listed fish farming stocks have plunged after Russia announced a ban on fish imports.
Norway's salmon producers face losing their biggest market as Moscow escalates its response to sanctions imposed by the United States and the European Union.
2014 had been a decent year for fish farmers, as prices soared to record highs.
Shares in Marine Harvest slipped by 10% while Salmar shares dipped 9%. Grieg Seafood fell 7.4% as the key export market was suddenly cut off.
Russia announced a ban on fruit, vegetables, meat, fish and dairy products from the US, EU, Australia, Canada and Norway in response to the latest round of Western sanctions.
"It looks like the import ban will affect most Norwegian seafood exports," said Are Kvistad, from the Norwegian Seafood Federation, as quoted by Reuters. "This will have serious consequences for Norwegian seafood businesses in the short term."
Norway produces around half of the world's farmed salmon, while 10% of its produce is exported to Russia. Its seafood exports were worth $1bn in 2013 and had been set to increase this year after a promising start.