Farmed fish are contained - in ponds, tanks or cages - as with all farmed animals. Just as in land-based farming, farm managers increasingly choose stocking densities and handling practices that optimize growth and health status while avoiding unnecessary suffering.
Questions are sometimes raised about welfare aspects of aquaculture production. Usually, such questions focus on three issues: stocking densities, the possibility to have ‘free-range’ aquaculture and the way farmed fish is slaughtered at harvest.
There are many definitions of animal welfare. One definition is based upon the Farm Animal Welfare Council’s “five freedoms”:
- Freedom from thirst, hunger and malnutrition
- Freedom from discomfort due to environment
- Freedom from pain, injury and disease
- Freedom to express normal behaviour for the species
- Freedom from fear and distress.
Scientific studies have identified operating indicators of fish welfare so that producers are able to measure the welfare status of their stock. The Freedom Food certification scheme of the RSPCA in the UK is a very good example of a welfare standard that has been built by on-farm dialogue with producers and which is now available for salmonid species.
Many species of fish, such as herring and mackerel, live in large shoals in the wild and are therefore used to very high densities. Keeping such fish in high densities on a farm will only become a problem if the water quality deteriorates, or if the fish are deprived of oxygen or exposed to disease. Fish farmers do their best to prevent such conditions since they will reduce production.
Fish farms holding fish at high stocking densities carefully monitor the oxygen in the water and maintain it at the optimum level for fish growth. Every effort is made to ensure that fish are kept in a healthy condition and that disease is prevented wherever possible, or identified and treated should it occur.
Stocking density has often been proposed as an indicator to measure welfare and there is considerable debate about its value. Also, since the 1980’s the volume of cages used for salmon culture in Northern Europe has increased considerably – in some cases more than 200 times, reducing densities and enhancing the ability for the fish to show natural behaviour. However, as land animals that are kept within fences, some limits on behaviour are necessary in farmed fish production.
“Ranching” – is an aquaculture technique whereby fish and shellfish are bred in captivity and then released into the wild to complete their life cycle before being harvested at some time in the future. Ranching has effectively been applied to Atlantic and Pacific salmon production, whereby juvenile fish have been reared from wild-caught eggs and sperm, raised in hatcheries and then released into specific rivers as smolt, allowed to migrate to sea and recaptured on their return to their river of origin.
Lobster ranching has also been tried on a number of commercial lobster beds in the past, with juvenile lobsters being raised in shore-based hatcheries and then placed on the seabed in sheltered rocky habitats where their chance of survival is thought to warrant the expense of production.
“Organic” salmon farming is conducted according to agreed codes of organic production. Rearing takes place in large, open water floating pens where conditions are as close to the open ocean as possible. Stocking densities are reduced to allow the fish to grow and develop in as natural a way as possible and the only feed used comes from sustainable fisheries. Because of lower stocking densities and open water conditions, the fish tend to be less prone to disease and therefore the use of medicines can be kept to a minimum. Increased production cost for “organic” fish is recouped with higher prices on the marketplace.
Shellfish farming, such as the laying of oysters and mussels directly on the seabed or the hanging of mussels on suspended ropes, can be said to be “free range” in so far as it is allowing the shellfish to grow in identical conditions to those they would encounter in the wild.
Recent studies suggest that fish, like warm-blooded animals, can experience fear and pain, leading to justifiable concern that codes of practice for the welfare of warm-blooded farm animals should be extended to cover farmed fish.
Accordingly, a four-step process for the humane slaughter of farmed fish has been developed similar to the European Directive covering warm-blooded animals. It covers transport and live storage, restraining, stunning and slaughter.
The process decrees that, to spare fish avoidable trauma, stunning prior to slaughter should induce immediate (within one second) and permanent loss of consciousness or, where loss of consciousness is not immediate, it should be without any avoidable excitement, pain or suffering.
Farmers currently employ any of three ways to reach this goal: electrical stunning (passing a current through the animal); mechanical stunning (a captive needle destroys the brain) or chemical stunning (adding a food-grade substance like eugenol, based on clove oil, to the water in which the fish are held.)
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