Fish farming in Norway
A typical Norwegian salmon farm
A typical Norwegian salmon farming locality consists of six to ten circular sea cages. Each sea cage will hold up to 200.000 salmon in a net that is 20-50 meters deep and 50 meters in diameter. The maximum stocking density is 25 kg/m3 (10 kg/m3 if organic), giving each conventionally produced salmon approximately one bathtub of water each. The largest sites will hold more than 2 million salmon per generation.
Intensive breeding has led to salmon growing to full size twice as fast as they did in the 1970s. Deformities due to breeding and fast growth leads to a proportion of farmed salmon experiencing severely compromised health and welfare.
With many individuals at each locality and many localities close together, disease had been a major challenge for Norwegian aquaculture. Although vaccinations have helped, certain diseases such as pancreas disease (PD), cardiomyopathy syndrome (CMS) and heart and skeletal muscle inflammation (HSMI) are prevalent. While disease can cause suffering and mortality by itself, stressful or harmful handling such as treatment for lice with hydrogen peroxide is known to cause mass mortality in diseased fish.
Salmon lice are prevalent. The main cause for concern for the industry is the increasing pressure from environmentalists to reduce parasitic burden for wild salmon. However, the lice do act as disease vectors as well as create infection pathways through the salmon skin, and so are also a direct concern for the industry itself. A maximum of 0.5 mature female lice per fish on average are allowed as per regulations.
In order to decrease reliance on, and use of, chemical louse treatments, the aquaculture industry increasingly relies on cleaner fish to control salmon lice. Cleaner fish are hailed as an environmentally friendly approach to delousing, and are used as part of a parasite control approach at half of all Norwegian localities. While some have raised concerns regarding the high mortality (near 100%), cleaner fish welfare remains very poor, and they are generally used as a disposable tool in salmon production.
Stress, handling and transportation
All handling of salmon can cause increased stress levels. Handling occurs during transportation, sorting, vaccination and medical treatment (e.g. chemical treatment for salmon lice). Not being able to escape aggressive individuals or poor environmental conditions can also cause stress for farmed salmon. Long term stress can inhibit normal behaviour and normal physiological processes. Recent studies have suggested that stress during transportation can be reduced by adding a sedative to the water.
Norwegian legislation requires farmed fish to be stunned prior to slaughter. Previously, CO2 was used for stunning, however this method was banned in 2012 following pressure from the Norwegian Animal Protection Alliance. CO2 is believed to cause a feeling of suffocation in fish. Today, two methods for stunning are used: electric stunning and percussive stunning.
- Breeding: Breeding should focus on healthy fish, and welfare must be prioritised over productivity in breeding goals.
- Reduced stocking density: The high stocking densities for conventionally produced salmon cause stress. Lower stocking densities is a possible improvement, however too low densities can cause territoriality and aggression. Lower stocking densities would also reduce the number of available hosts for parasites and disease, thus alleviating these severe problems that the industry is facing today.
- Avoid cleaner fish: Cleaner fish are used as a tool, and experience notoriously low welfare.
- Sedation during transport: Using a sedative during transport can lower stress levels. However, one should be aware that this can cause increased oxygen consumption and that oxygen levels must be closely monitored and extra oxygen added to water if necessary.
- "Dead haul": One processing boat (where salmon are slaughtered in a converted well boat) is in use in Norway, and there are plans for one more. Bringing the processing plant to the animals eliminates the highly stressful transportation stage. Processing boats are also more economic and better for disease control.