Aquaculture of salmonids

The aquaculture of salmonids is the farming and harvesting of salmonids under controlled conditions for both commercial and recreational purposes. Salmonids (particularly salmon and rainbow trout), along with carp, and tilapia are the three most important fish species in aquaculture. The most commonly commercially farmed salmonid is the Atlantic salmon. In the U.S. Chinook salmon and rainbow trout are the most commonly farmed salmonids for recreational and subsistence fishing through the National Fish Hatchery System. In Europe, brown trout are the most commonly reared fish for recreational restocking. Commonly farmed nonsalmonid fish groups include tilapia, catfish, sea bass, and bream.

In 2007, the aquaculture of salmonids was worth US$10.7 billion globally. Salmonid aquaculture production grew over ten-fold during the 25 years from 1982 to 2007. In 2012, the leading producers of salmonids were Norway, Chile, Scotland and Canada.

Much controversy exists about the ecological and health impacts of intensive salmonids aquaculture. Of particular concern are the impacts on wild salmon and other marine life.

Methods

The aquaculture or farming of salmonids can be contrasted with capturing wild salmonids using commercial fishing techniques. However, the concept of "wild" salmon as used by the Alaska Seafood Marketing Institute includes stock enhancement fish produced in hatcheries that have historically been considered ocean ranching. The percentage of the Alaska salmon harvest resulting from ocean ranching depends upon the species of salmon and location. Methods of salmonid aquaculture originated in late 18th-century fertilization trials in Europe. In the late 19th century, salmon hatcheries were used in Europe and North America. From the late 1950s, enhancement programs based on hatcheries were established in the United States, Canada, Japan, and the USSR. The contemporary technique using floating sea cages originated in Norway in the late 1960s.

Salmonids are usually farmed in two stages and in some places maybe more. First, the salmon are hatched from eggs and raised on land in freshwater tanks. Increasing the accumulated thermal units of water during incubation reduces time to hatching. When they are 12 to 18 months old, the smolt (juvenile salmon) are transferred to floating sea cages or net pens anchored in sheltered bays or fjords along a coast. This farming in a marine environment is known as mariculture. There they are fed pelleted feed for another 12 to 24 months, when they are harvested.

Norway produces 33% of the world's farmed salmonids, and Chile produces 31%. The coastlines of these countries have suitable water temperatures and many areas well protected from storms. Chile is close to large forage fisheries which supply fish meal for salmon aquaculture. Scotland and Canada are also significant producers; and it was reported in 2012 that the Norwegian government at that time controlled a significant fraction of the Canadian industry.

Modern salmonid farming systems are intensive. Their ownership is often under the control of huge agribusiness corporations, operating mechanized assembly lines on an industrial scale. In 2003, nearly half of the world’s farmed salmon was produced by just five companies.

Hatcheries

Modern commercial hatcheries for supplying salmon smolts to aquaculture net pens have been shifting to recirculating aquaculture systems (RAS)s where the water is recycled within the hatchery. This allows location of the hatchery to be independent of a significant fresh water supply and allows economical temperature control to both speed up and slow down the growth rate to match the needs of the net pens.

Conventional hatchery systems operate flow-through, where spring water or other water sources flow into the hatchery. The eggs are then hatched in trays and the salmon smolts are produced in raceways. The waste products from the growing salmon fry and the feed are usually discharged into the local river. Conventional flow-through hatcheries, for example the majority of Alaska's enhancement hatcheries, use more than of water to produce a kg of smolts.

An alternative method to hatching in freshwater tanks is to use spawning channels. These are artificial streams, usually parallel to an existing stream with concrete or rip-rap sides and gravel bottoms. Water from the adjacent stream is piped into the top of the channel, sometimes via a header pond to settle out sediment. Spawning success is often much better in channels than in adjacent streams due to the control of floods which in some years can wash out the natural redds. Because of the lack of floods, spawning channels must sometimes be cleaned out to remove accumulated sediment. The same floods which destroy natural redds also clean them out. Spawning channels preserve the natural selection of natural streams as no temptation exists, as in hatcheries, to use prophylactic chemicals to control diseases. However, exposing fish to wild parasites and pathogens using uncontrolled water supplies, combined with the high cost of spawning channels, makes this technology unsuitable for salmon aquaculture businesses. This type of technology is only useful for stock enhancement programs.

Sea cages

Sea cages, also called sea pens or net pens, are usually made of mesh framed with steel or plastic. They can be square or circular, across and deep, with volumes between . A large sea cage can contain up to 90,000 fish.

They are usually placed side by side to form a system called a seafarm or seasite, with a floating wharf and walkways along the net boundaries. Additional nets can also surround the seafarm to keep out predatory marine mammals. Stocking densities range from /m³ for Atlantic salmon and /m³ for Chinook salmon.

In contrast to closed or recirculating systems, the open net cages of salmonid farming lower production costs, but provide no effective barrier to the discharge of wastes, parasites, and disease into the surrounding coastal waters. Farmed salmon in open net cages can escape into wild habitats, for example, during storms.

An emerging wave in aquaculture is applying the same farming methods used for salmonids to other carnivorous finfish species, such as cod, bluefin tuna, halibut, and snapper. However, this is likely to have the same environmental drawbacks as salmon farming.

A second emerging wave in aquaculture is the development of copper alloys as netting materials. Copper alloys have become important netting materials because they are antimicrobial (i.e., they destroy bacteria, viruses, fungi, algae, and other microbes), so they prevent biofouling (i.e., the undesirable accumulation, adhesion, and growth of microorganisms, plants, algae, tubeworms, barnacles, mollusks, and other organisms). By inhibiting microbial growth, copper alloy aquaculture cages avoid costly net changes that are necessary with other materials. The resistance of organism growth on copper alloy nets also provides a cleaner and healthier environment for farmed fish to grow and thrive.

Feeding

With the amount of worldwide fish meal production being almost a constant amount for the last 30+ years and at maximum sustainable yield, much of the fish meal market has shifted from chicken and pig feed to fish and shrimp feeds as aquaculture has grown in this time.Shepherd, Jonathan; Jackson, Andrew and Mittaine, Jean-Francois (July 4, 2007
Fishmeal industry overview
International Fishmeal and Fish Oil Organisation.

Work continues on developing salmonid diet made from concentrated plant protein. As of 2014, an enzymatic process can be used to lower the carbohydrate content of barley, making it a high-protein fish feed suitable for salmon. Many other substitutions for fish meal are known, and diets containing zero fish meal are possible. For example, a planned closed-containment salmon fish farm in Scotland uses ragworms, algae, and amino acids as feed. Some of the eicosapentaenoic acid and docosahexaenoic acid (in Omega-3 fatty acids) may be replaced by land-based (non-marine) algae oil, reducing the harvest of wild fish as fish meal.

However, commercial economic animal diets are determined by least-cost linear programming models that are effectively competing with similar models for chicken and pig feeds for the same feed ingredients, and these models show that fish meal is more useful in aquatic diets than in chicken diets, where they can make the chickens taste like fish. Unfortunately, this substitution can result in lower levels of the highly valued omega-3 content in the farmed product. However, when vegetable oil is used in the growing diet as an energy source and a different finishing diet containing high omega-3 content fatty acids from either fish oil, algae oils, or some vegetable oils are used a few months before harvest, this problem is eliminated.

On a dry-dry basis, 2–4 kg of wild-caught fish are needed to produce 1 kg of salmon. The ratio may be reduced if non-fish sources are added. Wild salmon require about 10 kg of forage fish to produce 1 kg of salmon, as part of the normal trophic level energy transfer. The difference between the two numbers is related to farmed salmon feed containing other ingredients beyond fish meal and because farmed fish do not expend energy hunting.

In 2017 it was reported that the American company Cargill has been researching and developing alternative feeds with EWOS through its internal COMPASS programs in Norway, resulting in the proprietary RAPID feed blend. These methods studied macronutrient profiles of fish feed based upon geography and season. Using RAPID feed, salmon farms reduced the time to maturity of salmon to about 15 months, in a period one-fifth faster than usual.

Other feed additives

, 50-80% of the world fish oil production is fed to farmed salmonids.

Farm raised salmonids are also fed the carotenoids astaxanthin and canthaxanthin, so their flesh colour matches wild salmon, which also contain the same carotenoid pigments from their diet in the wild.

Harvesting

Modern harvesting methods are shifting towards using wet-well ships to transport live salmon to the processing plant. This allows the fish to be killed, bled, and filleted before rigor has occurred. This results in superior product quality to the customer, along with more humane processing. To obtain maximum quality, minimizing the level of stress is necessary in the live salmon until actually being electrically and percussively killed and the gills slit for bleeding.Modern Salmon Harvest
The Fishery and Aquaculture Industry Research Fund (2010) These improvements in processing time and freshness to the final customer are commercially significant and forcing the commercial wild fisheries to upgrade their processing to the benefit of all seafood consumers.

An older method of harvesting is to use a sweep net, which operates a bit like a purse seine net. The sweep net is a big net with weights along the bottom edge. It is stretched across the pen with the bottom edge extending to the bottom of the pen. Lines attached to the bottom corners are raised, herding some fish into the purse, where they are netted. Before killing, the fish are usually rendered unconscious in water saturated in carbon dioxide, although this practice is being phased out in some countries due to ethical and product quality concerns. More advanced systems use a percussive-stun harvest system that kills the fish instantly and humanely with a blow to the head from a pneumatic piston. They are then bled by cutting the gill arches and immediately immersing them in iced water. Harvesting and killing methods are designed to minimize scale loss, and avoid the fish releasing stress hormones, which negatively affect flesh quality.

Wild versus farmed

Wild salmonids are captured from wild habitats using commercial fishing techniques. Most wild salmonids are caught in North American, Japanese, and Russian fisheries. The following table shows the changes in production of wild salmonids and farmed salmonids over a period of 25 years, as reported by the FAO. Russia, Japan and Alaska all operate major hatchery based stock enhancement programs. The resulting fish hatchery fish are defined as "wild" for FAO and marketing purposes.

Issues

The US in their dietary guidelines for 2010 recommends eating 8 ounces per week of a variety of seafood and 12 ounces for lactating mothers, with no upper limits set and no restrictions on eating farmed or wild salmon.
In 2018, Canadian dietary guidelines recommended eating at least two servings of fish each week and choosing fish such as char, herring, mackerel, salmon, sardines, and trout.

Currently, much controversy exists about the ecological and health impacts of intensive salmonid aquaculture. Of particular concern are the impacts on wild salmonids and other marine life and on the incomes of commercial salmonid fishermen.Pirquet, K. T. (May/June 2010
"Follow the Money"
Aquaculture North America, vol 16 However, the 'enhanced' production of salmon juveniles – which for instance lead to a double-digit proportion (20-50%) of the Alaska's yearly ‘wild’ salmon harvest - is not void of controversy, and the Alaska salmon harvest are highly dependent on the operation of Alaska’s Regional Aquaculture Associations. Furthermore, the sustainability of enhanced/hatchery-based ‘wild’ caught salmon has long been hotly debated, both from a scientific and political/marketing perspective. Such debate and positions were central to a 'halt' in the re-certification of Alaska salmon fisheries by the Marine Stewardship Council (MSC) in 2012. The Alaska salmon fisheries subsequently re-attained MSC-certification status; however the heavily hatchery-dependent Prince William Sound (PWS) unit of certification (“one of the most valuable fishing area in the State”) was for several years excluded from the MSC-certification (it remained ‘under assessment’ pending further analysis).

Disease and parasites

In 1972, ''Gyrodactylus'', a monogenean parasite, was introduced with live trout and salmon from Sweden (Baltic stocks are resistant to it) into government-operated hatcheries in Norway. From the hatcheries, infected eggs, smolt, and fry were implanted in many rivers with the goal to strengthen the wild salmon stocks, but caused instead devastation to some of the wild salmon populations affected.

In 1984, infectious salmon anemia (ISAv) was discovered in Norway in an Atlantic salmon hatchery. Eighty percent of the fish in the outbreak died. ISAv, a viral disease, is now a major threat to the viability of Atlantic salmon farming. It is now the first of the diseases classified on List One of the European Commission’s fish health regimen. Amongst other measures, this requires the total eradication of the entire fish stock should an outbreak of the disease be confirmed on any farm. ISAv seriously affects salmon farms in Chile, Norway, Scotland, and Canada, causing major economic losses to infected farms. As the name implies, it causes severe anemia of infected fish. Unlike mammals, the red blood cells of fish have ribosomes, and can become infected with viruses. The fish develop pale gills, and may swim close to the water surface, gulping for air. However, the disease can also develop without the fish showing any external signs of illness, the fish maintain a normal appetite, and then they suddenly die. The disease can progress slowly throughout an infected farm, and in the worst cases, death rates may approach 100%. It is also a threat to the dwindling stocks of wild salmon. Management strategies include developing a vaccine and improving genetic resistance to the disease.

In the wild, diseases and parasites are normally at low levels, and kept in check by natural predation on weakened individuals. In crowded net pens, they can become epidemics. Diseases and parasites also transfer from farmed to wild salmon populations. A recent study in British Columbia links the spread of parasitic sea lice from river salmon farms to wild pink salmon in the same river. The European Commission (2002) concluded, "The reduction of wild salmonid abundance is also linked to other factors but there is more and more scientific evidence establishing a direct link between the number of lice-infested wild fish and the presence of cages in the same estuary." It is reported that wild salmon on the west coast of Canada are being driven to extinction by sea lice from nearby salmon farms. These predictions have been disputed by other scientists and recent harvests have indicated that the predictions were in error. In 2011, Scottish salmon farming introduced the use of farmed wrasse for the purpose of cleaning farmed salmon of ectoparasites.

Globally, salmon production fell around 9% in 2015, in large part due to acute outbreaks of sea lice in Scotland and Norway. Lasers are used to reduce lice infections.

In the mid 1980s to the 1990s, bacterial kidney disease (BKD) caused by '' Renibacterium salmoninarum'' heavily impacted Chinook hatcheries in Idaho. The disease causes granulomatous inflammation that can lead to abscesses in the liver, spleen, and kidney.

Pollution and contaminants

Salmonid farms are typically sited in marine ecosystems with good water quality, high water exchange rates, current speeds fast enough to prevent pollution of the bottom but slow enough to prevent pen damage, protection from major storms, reasonable water depth, and a reasonable distance from major infrastructure such as ports, processing plants, and logistical facilities such as airports. Logistical considerations are significant, and feed and maintenance labor must be transported to the facility and the product returned. Siting decisions are complicated by complex, politically driven permit problems in many countries that prevents optimal locations for the farms.

In sites without adequate currents, heavy metals can accumulate on the benthos

HOME


Content is Copyleft
Website design, code, and AI is Copyrighted (c) 2014-2017 by Stephen Payne


Consider donating to Wikimedia



As an Amazon Associate I earn from qualifying purchases