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Aquaculture

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Aquaculture is the cultivation of the natural produce of water (such as fish or shellfish, algae and other aquatic plants). Mariculture is specifically marine aquaculture, and thus is a subset of aquaculture. Some examples of aquaculture include raising catfish and tilapia in freshwater ponds, growing cultured pearls, and farming salmon in net-pens set out in a bay. Fish farming is a common kind of aquaculture.

History Edit

Aquaculture was used in China circa 2500 BC. When the waters lowered after river floods some fishes, namely carps, were held in artificial lakes. Their brood were later fed using nymphs and feces from silkworms used for silk production.

The Romans were quite adept in breeding fish in ponds. In Europe it became common again in monasteries during the Middle Ages, since fish was scarce and thus expensive. The 19th century's transportation improvements made fish easily available and inexpensive, even far from the seas, causing a decline in aquaculture.

The current boom started in the 1960s after overfishing caused another price rise. Today, commercial aquaculture exists on a huge scale previously unknown, causing controversy because of its effects on the public waters beyond the boundaries of the pens.

BenefitsEdit

Aquaculture has been one of the fastest growing segments of global food production in recent decades, and has been hailed as an answer to declining wild fish stocks caused largely by overfishing.

Fish and other aquacultured species are generally very efficient converters of feedstuffs into high quality protein when compared to other farmed animals. For example a catfish may take 6kg of feed (wet weight to wet weight) to produce 1kg of catfish whereas a chicken might take 10kg and a pig 30kg. This is possible primarily because aquaculture species are cold-blooded (or more corectly - poikilothermic),and hence do not waste energy on heating, and because the physics of the aquatic environmment require little energy for movement. Fish and other aquacultured species also tend to be comprised of a higher percentage of edible weight than terrestrial species.

Farming of high value (and often overexploited) species can reduce presure on wild stocks. While most consumers claim that wild examples of a species taste better, blind tasting experiments have repeatingly found farmed seafood to be equal to, or even better in taste to, the wild caught equivalent.

There are inumerable aquatic species farmed in small quantities around the world. Major aquaculture industries around the world include (Appology: latin names are from top of head and may be mis-spelt):

Atlantic salmon (Salmo salar)and Rainbow trout (Oncorynkiss mykiss). Also smaller volumes of a variety of other salmonids. Originally developed in Norway, Denmark (Rainbow trout although it is an American species) and Scotland, now farmed in significant quatities in Europe, Canada, Chile and Australia (Tasmania). First or Second in the world for production value.

Tropical shrimp; Mostly Black tiger shrimp (Penaeus monodon)and increasingly White shrimp (Litopenaeus vannemi). Techniques originally developed in Japan and Taiwan. Mostly farmed through tropical and sub-tropical Asia and South America. First or Second in the world for production value.

Carps; European carp, Chinese carps (Grass, Silver and Black) and Indian major carps are easily the largest global aquaculture industry by volume of production but are low in value. Major producers are China, India, Southeat Asia and Europe. China's reported production figures are considered contentious by some authorities. Value of production is also debatable acording to whether value is calculated at border (exchange rate) prices or PPP (Purchasing Power Parity) prices. None-the-less carps are major contributors of high quality protein to the diets of poorer people around the world.

Seaweeds; Many species. Huge volumes, low value. Mostly farmed in Asia; particuarly Japan, Korea and China.

Catfish; Major species are Vietmanese basa (), Channel catfish and African and Asian walking catfish (Clarias sp.). Mostly farmed in Asia and the Southern United States.

Tilapia; Nile tilapia and a few other species. Very well suited species to subsistance farming although arguably not well suited to large aquabusiness due to finicky breeding biology and low flesh recovery (Although becoming a very succesful import in the US and Europe). Mostly farmed in Asia, South America and Africa.

Oysters; Pacific oyster (Crassostrea gigas), American oyster (Crassostrea virginica), Flat oyster (Ostrea edulis) and others. Mostly farmed in Asia, US, Australia-New Zealand and Europe. Flat oyster was once a huge industry and low cost/very high quality food for the masses in Europe but collapsed under mortalities brought about by the parasite Bonamia.

Mussels; Blue mussel (Mytilus edulis), Green mussels (Perna sp.) Mostly farmed in Europe, Asia, New Zealand and South America.

It should be noted that many of these industries are based in developing countries and contribute greatly to food security/quality and income in these areas. Of the industries summarised above it should also be noted that all but Tropical shrimp and salmonids have a low level environmental impact. The environmental footprint exerted by the Tropical shrimp and salmonid industries is also rapidly improving.

Tuna farming in [[Australia] has had immense financial success. Tuna farming at present is really a fattening enterprise, where wild bred juvenile tuna are captured and grown in pens to a larger size and better flesh quality. Having the fish confined in pens also means that harvests can be timed to suit the market. This practice has resulted (at least in Australia) on reduced pressure on wild populations and a much larger value for their relatively small wild (Southern bluefin) tuna quota. Relatively recently, researchers in Japan have closed the life cycle of the Pacific bluefin tuna, and European researchers in Spain are working on breeding Northern bluefin tuna.

While the negative impacts of some aquaculture on the environment has been widely publicised (and arguably embelished), the positive environmental effects of aquaculture are rarely noted. For example many aquacultured species are highly sensitive to water quality conditions and aquaculture farmers often notice the effects of pollution or reductions in water quality before other authorities. Aquaculture businesses have a vested interest in clean waterways, in that a reduction in water quality has a direct effect on their production rates and financial bottom line. Appropriate aquaculture development can serve as 'canaries' for the health of waterways, with farms often conducting very regular and quite sophisticated monitoring of their aquatic environment.

Large scale aquaculture is a very new and undeveloped industry when compared to terrestrial aquacultures. Only a few species (Atlantic salmon, Pacific white shrimp and possibly several species each of catfish, carp and tilapia) are currently on their way to becoming true domesticated aquabuisiness species in the way that poultry, beef and pork have long been. While the aquaculture industry is still only a small way into the development curve the inherent biological characteristics of aquatic animals bode well for the future contribution of aquatic farming to living standards and the environment.

ChallengesEdit

In countries like the U.K., Canada, Norway, and Chile, salmon and trout farming are one of the fastest-growing forms of agriculture. Salmon farming is not increasing in the United States because of heavy competition from other countries, and higher environmental standards for fish farms in the US. Salmon farming, like other food producing operations such as beef, wheat or tomatoes can impact the environment.

However, the difference between shore farming and fish farming is that shore farming takes place on private land, while fish farming often takes place on the public waters. Organic wastes from fish cages can have a significant effect on water quality and the population structure of organisms, beyond the boundaries of the fish pens, increasing the occurrence of toxic algal blooms. Scotland, as well as Chile and China, has had serious toxic algae blooms. Algal blooms can cause the death of huge numbers of wild fish and other species, and great harm to wild fisheries. However, even a month of fallow time can return the area to pristine condition.

Like other agriculture production, aquaculture must stand up to a rigorous evaluation of any environmental impact. Salmon aquaculture has come under increasing scrutiny from environmental nongovernmental organizations (ENGO's). In Canada, salmon farming sites occupy a small portion of the coastal zone areas where they are located. The total area occupied by Canadian salmon farms in British Columbia and the Bay of Fundy in New Brunswick is about 8,900 acres (36 km²) which is less than 0.01% of the coastal area where these sites are located. Still, even though salmon farms occupy only a small percentage of the public waters, scientists have found a significant degradation of the areas where they exist, with lowered oxygen levels, replacement of native seaweeds with invasive seaweeds, increased algal blooms, reduction of wild species, and loss of nursery habitat for wild fish.

Wild Pacific and Atlantic salmon stocks have seen significant declines over the last several decades, before salmon farming operations started. These declines were caused by a combination of factors including climate change, overfishing and freshwater habitat destruction. However, rivers with fish farms have experienced accelerated decline of wild stocks caused by spread of diseases such as infectious salmon anemia, and parasites such as sea lice from farmed to wild salmon.

Concerns have been raised on the East coast that wild Atlantic salmon may interbreed with and catch disease from salmon that escape from farms. Canadian salmon farmers have significantly reduced the escape of their salmon. The evidence shows that the escape of farmed salmon on Canada's west coast poses low risk to Pacific salmon. However, young wild salmon swimming down river to the ocean are free of sea lice parasites before they swim past the salmon farms, and laden with sea lice after they pass the farms. Most die from these sea lice.

Many farmed fish species are carnivorous, meaning that other wild fish species must be harvested to maintain the fish farm. For example, herring are used to make salmon feed. Since herring are the backbone of the North Atlantic food chain, increased fishing pressure on their numbers is a serious threat to all other fish species which depend on herring for food. It is argued that fish farms, far from removing the pressure on wild fish stocks, increase it. Others argue that it takes less fish (in the form of the fishmeal component of an aquaculture diet) to produce a unit of table fish through aquaculture than through the natural food web. Fisheries that are based on species lower on the trophic web (such as many species used for fishmeal) are also more resistent to overfishing than typical table fish fisheries.

The fish farm industry is trying to decrease its reliance on fish for fish feed. The vast majority of aquaculture production on the global scale (species such as carps, catfish and tilapia) occurs with the use of feeds with very little or no fishmeal. A portion of the fish meal used in fish feeds for highly carnivorous species comes from the trimmings and discards of commercial species. More studies are being done concerning shifts in feed composition using poultry and vegetable oils as substitutes for fish protein & oil. However this use of land based feed ingredients results in a decrease of the Omega 3 fish oils in the farmed fish (although in some cases a 'washing out' of the terrestrial oils can be acheived with a short period of feeding with marine oils prior to harvest). The current relectance to further reduce fishmeal and marine oils in the commercial diets of species such as the salmonids and shrimps is not based so much on technical difficulties as consumer resistance to the taste and health qualities of vegetarian fish. In the long term, alternative sources of long chain Omega 3 fatty acids (the most difficult ingredient to source from non fish sources) may be developed from zooplankton or microalgal origins.

Other problems with aquaculture include the potential for increasing the spread of unwanted invasive species, as farmed species are often not native to the area in which they are farmed. When these species escape, they can compete with native species and damage ecosystems. Another problem is the spread of introduced parasites, pests, and diseases.

See also: fishery

ReferencesEdit

External linksEdit

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