Documents seen by IntraFish show that fish that escaped from SalMar's Ocean Farm 1 in two recent incidents had Heart and Skeletal Muscle Inflammation (HSMB) disease.

How many fish escaped from the company's offshore Ocean Farm 1 near Froya in Norway is unknown, as numbers imply the number of fish harvested from the cage after the incident was higher than the number of smolt released into it -- a clear error in counting at some point during the cycle.

HSMB is one of the most common viral diseases in the Norwegian salmon industry. In 2019, the veterinary institute registered 139 cases of diseases, but the disease is not notifiable, so the incidence is probably much higher.

According to the Norwegian Veterinary Institute, fish with the disease can have major damage to the heart without showing any external symptoms. In case of disease outbreaks, mortality in the fish farm increases, with loss in affected cages varying from insignificant amounts to around 20 percent.

SalMar was at the lower end of this, with 54,125 dead fish retrieved from the farm during the production cycle. Of a recorded count of 1.2 million smolt released into the cage, this gives a mortality rate of around 4.6 percent, far lower even than the average mortality rate in the Norwegian fish farming industry which, according to a recent article from Nova Sea owner Aino Olaisen, sits at around 20 percent.

The report from SalMar does not reveal what the 54,125 dead fish died from.