Salmon aquaculture is the cultivation of salmon in environments controlled by humans, which can be contrasted to fishing practices that harvest salmon in the wild. The practices used in salmon aquaculture may vary, but the most common methods involve hatching the salmon and keeping them in sea cages that prevent the fish from swimming away. Less commonly, fish may be spawned and released into the wild with the intention of increasing the overall number of fish available. There are many concerns about the negative effects of salmon aquaculture on wild fish populations as well as on the marine environments in which farming occurs.
The methods used to farm salmon usually involve breeding from a selected stock of fish. Eggs and sperm are harvested from salmon of good stock and are fertilized under controlled environments. The hatchlings resulting from this breeding program are usually raised in freshwater tanks for a number of months until they are mature enough for sea cages. Juvenile salmon typically live in these freshwater tanks for a year or more before they are moved to salt water.
One of the most important innovations in salmon aquaculture was the invention of the floating sea cage. These cages keep fish from escaping, but must be placed in gentle bays that are protected from storms in order to function properly. This makes countries such as Norway and Chile particularly popular for salmon aquaculture, as suitable marine areas are common in these countries.
During life in the sea cages, the salmon must be fed fish food made from other fish because salmon are carnivores. Salmon are kept in the sea cages for a year or two and are then harvested using nets. The fish are typically killed where they are raised, unlike practices in many other animal farming operations. There are no salmon slaughterhouses, which means that companies involved in salmon aquaculture must be able to safely and effectively harvest the fish for human consumption as well. Usually, the fish are killed quickly and humanely, both for the fish's benefit and because fish release hormones when stressed that decrease the quality of their flesh.
Some groups, however, engage only in the hatching part of salmon aquaculture. These groups believe that by hatching and releasing the fish into rivers, the natural wild salmon population can be at least partially restored. This is usually not a very good business plan for companies, as anyone can catch the salmon, reducing the chances for profit. For groups that are concerned not only with profit but also environmental health, this method of raising salmon provides the positive impact of a healthy salmon population without many of the negative environmental effects of salmon farming.