Norway-based salmon farmer SinkabergHansen lost 90 percent of the fish in two of its netpens during a storm in February along the Helgeland coast in northern Norway.
The extreme weather caused power outages and darkened netpens.
"One response the fish can have when the light suddenly disappears is that it searches downwards," the company said in a report to The Norwegian Food Safety Authority. "The consequences of this are high fish density, which in turn means that the fish don't get sufficient water flow over the gills which leads to reduced oxygen uptake."
