What’s behind your local salmon?

Infectious diseases and injuries due (also) to overcrowding: in Norway's intensive farms, salmon die before they reach slaughter at a shocking rate. In 2023, 62.8 million salmon (and 2.5 million rainbow trout) died in the marine production phase

Have you ever wondered what’s behind the salmon at your local fishmonger? Diseases of the pancreas, gills, and heart or injuries incurred during the removal of parasites like sea lice. Only the “lucky” ones survive (and we eat them), while the rest face alarming numbers and an early mortality that is chilling.

Last year, nearly 63 million salmon died prematurely in large farms nestled among the fjords of Norway, the world’s largest producer of Atlantic salmon. This number corresponds to a mortality rate of 16.7%, also at a record level, and is a gradually increasing figure that poses an economic problem for producers.

The Norwegian Veterinary Institute’s annual report

According to the annual fish health report from the Norwegian Veterinary Institute, the number of salmon that died in the so-called “sea phase” of farming, i.e., when the fish live within coastal enclosures, also included 2.5 million rainbow trout.

The high mortality rates are a known issue for this type of farming, especially prevalent in Norway and Chile but also common in other countries such as Scotland, Iceland, Faroe Islands, and Canada.

Why do salmon die?

The number one problem is the speed at which the fish are raised, as they are subjected to stress from birth in freshwater until slaughter. During the first freshwater phase, light and temperature are manipulated so that they grow quickly, a phase that in nature lasts from two to six years, whereas in farming, it takes from six months to a year.

The main causes of salmon deaths are diseases, which can be due to viruses, bacteria, and parasites, but the conditions of the marine environment where the nets are located also play a significant role. Peaks in mortality also occur following events such as jellyfish attacks, heatwaves, or excessive development of certain algae.

More specifically, the main causes of mortality recorded at the national level were:

  • Infectious diseases, about 38%, such as ulcers, cardiomyopathy syndrome, gill diseases, heart and skeletal muscle inflammation (HSMB), and pasteurellosis. Treatments against lice and stressful handling can weaken the fish and make them more susceptible to these types of infectious diseases
  • Injuries (trauma), about 33%
  • Unknown causes, about 20%
  • Physiological causes, 4.5%
  • Environmental conditions, 2.9%

Salmon diseas

In 2023, 355 locations with edible salmon participated in the analyses, corresponding to 43% of the permanent mass at sea.

Furthermore, the reports show large geographical differences in mortality: for salmon destined for the food industry in 2023, production area 3 (PO3) was the worst with 25%, followed by PO2 with 22%, while PO13, PO1, and PO11 all had a mortality rate below 10%.

Mortality in the fry stage

In 2023, the number of incubation fish that died (over 0.1 ounces) was approximately 37.7 million salmon (and 2.4 million rainbow trout). This represents an increase of about 2 million salmon compared to 2022. For rainbow trout, there was a slight decrease in both the number of dead fish reported and the number released. The way data are reported makes it difficult to calculate the annual percentage of mortality in the incubation phase.

“Our conclusion for 2023 is that total mortality has slowly increased over the last 5-6 years, reaching a historic maximum for 2023 with about 63 million fish dead in the growth phase at sea,” says Edgar Brun, Director for Aquatic Animal Health and Welfare at the Norwegian Veterinary Institute. There are some positive results, but the main trend regarding diseases and fish welfare is not improving. Skin lesions caused by mechanical treatment of salmon lice and bacterial infections are one of the main causes of high mortality.

What happens to sick salmon?

Certainly, they are not thrown away but are transformed into animal feed or even biofuel.

None of the pathogens causing diseases in salmon produced in Norway affect human health; moreover, the production of Norwegian salmon almost never involves the use of antibiotics, so regarding various salmon diseases, nothing harmful is ending up on our plates, concludes Brun.

Condividi su Whatsapp Condividi su Linkedin