Aquaculture, also known as aquafarming, is the farming of
aquatic organisms such as fish, crustaceans, molluscs and aquatic plants.
Aquaculture involves cultivating freshwater and saltwater populations under
controlled conditions, and can be contrasted with commercial fishing, which is the harvesting of wild fish.
Broadly speaking, finfish and shellfish fisheries can be conceptualized as akin
to hunting and gathering while aquaculture is akin to agriculture.
Mariculture
refers to aquaculture practiced in marine environments and in underwater
habitats.
According to the FAO, aquaculture "is understood to mean the farming of
aquatic organisms including fish, molluscs, crustaceans and aquatic plants.
Farming implies some form of intervention in the rearing process to enhance
production, such as regular stocking, feeding, protection from predators, etc.
Farming also implies individual or corporate ownership of the stock being
cultivated.
The reported output from global aquaculture operations would supply one half of
the fish and shellfish that is directly consumed by humans;
however, there are issues about the reliability of the reported figures.
Further, in current aquaculture practice, products from several pounds of wild
fish are used to produce one pound of a piscivorous
fish like salmon.
Particular kinds of aquaculture
include fish farming, shrimp farming, oyster farming,
algaculture
(such as seaweed farming), and the cultivation of ornamental fish.
Particular methods include aquaponics
and integrated
multi-trophic aquaculture, both of
which integrate fish farming and plant farming.
History
The
indigenous Gunditjmara people in Victoria, Australia may have raised eels
as early as 6000 BC. There is evidence that they developed about 100
square kilometres (39 sq mi) of volcanic floodplains in the vicinity of Lake Condah into a complex of
channels and dams, that they used
woven traps to capture eels, and preserve eels to eat all year
round.
Aquaculture
was operating in China circa 2500 BC. When the waters
subsided after river floods, some fishes, mainly
carp, were trapped in lakes. Early aquaculturists fed their brood
using nymphs and silkworm feces, and ate them.
A fortunate genetic mutation of carp led to the emergence
of goldfish during the Tang Dynasty.
Japanese
cultivated seaweed by providing bamboo poles and, later,
nets and oyster shells to serve as
anchoring surfaces for spores.
Romans bred fish in ponds.
In
central Europe, early Christian monasteries adopted Roman
aquacultural practices. Aquaculture spread
in Europe during the Middle Ages since away from the
seacoasts and the big rivers fish had to be salted in order to not perish. Improvements in
transportation during the 19th century made fresh fish easily available and
inexpensive, even in inland areas, making aquaculture less popular.
Hawaiians
constructed oceanic fish
ponds
(see Hawaiian
aquaculture).
A remarkable example is a fish pond dating from at least 1,000 years ago,
at Alekoko. Legend says that it was constructed by the mythical Menehune dwarf people.
In
1859 Stephen Ainsworth of West Bloomfield, New York, began experiments with brook trout. By 1864 Seth Green
had established a commercial fish hatching operation at Caledonia Springs, near
Rochester,
New York.
By 1866, with the involvement of Dr. W. W. Fletcher of Concord,
Massachusetts,
artificial fish hatcheries were under way in both Canada and the United States. When the Dildo Island fish hatchery opened
in Newfoundland in 1889, it was the largest and most advanced in the world.
Californians
harvested wild kelp and attempted to
manage supply circa 1900, later labeling it a wartime resource.
21st-century practice
About
430 (97%) of the species cultured as of 2007
were domesticated during the 20th century, of which an estimated 106 came in
the decade to 2007. Given the long-term importance of agriculture, it is
interesting to note that to date only 0.08% of known land plant species and
0.0002% of known land animal species have been domesticated, compared with
0.17% of known marine plant species and 0.13% of known marine animal species.
Domestication typically involves about a decade of scientific research. Domesticating
aquatic species involves fewer risks to humans than land animals, which took a
large toll in human lives. Most major human diseases originated in domesticated
animals, through diseases
such as smallpox and diphtheria, that like most
infectious diseases, move to humans from animals. No human pathogens of comparable
virulence have yet emerged from marine species.
Harvest
stagnation in wild
fisheries
and overexploitation of popular marine
species, combined with a growing demand for high quality protein, encourage
aquaculturists to domesticate other marine species.
Species groups
Aquatic plants
Microalgae, also referred to as
phytoplankton, microphytes, or planktonic algae constitute the
majority of cultivated algae.
Macroalgae, commonly known as seaweed, also have many commercial
and industrial uses, but due to their size and specific requirements, they are
not easily cultivated on a large scale and are most often taken in the wild.
Fish
The
farming of fish is the most common form of aquaculture. It involves raising
fish commercially in tanks, ponds, or ocean enclosures, usually for food. A
facility that releases juvenile fish into the wild for recreational fishing or to supplement a
species' natural numbers is generally referred to as a fish hatchery. Worldwide, the most
important fish species used in fish farming are, in order, carp, salmon, tilapia and catfish.
In
the Mediterranean, young bluefin
tuna
are netted at sea and towed slowly towards the shore. They are then interned in
offshore pens where they are further grown for the market. In 2009, researchers
in Australia managed for the
first time to coax tuna (Southern
bluefin)
to breed in landlocked tanks.
Crustaceans
Commercial
shrimp farming began in the
1970s, and production grew steeply thereafter. Global production reached more
than 1.6 million tonnes in 2003, worth about 9 billion U.S.
dollars.
About 75% of farmed shrimp is produced in Asia, in particular in China and Thailand. The other 25% is
produced mainly in Latin
America,
where Brazil is the largest
producer. Thailand is the largest exporter.
Shrimp
farming has changed from its traditional, small-scale form in Southeast Asia into a global
industry. Technological advances have led to ever higher densities per unit
area, and broodstock is shipped
worldwide. Virtually all farmed shrimp are penaeids (i.e., shrimp of the
family Penaeidae), and just two
species of shrimp, the Pacific white shrimp and the giant tiger prawn, account for about
80% of all farmed shrimp. These industrial monocultures are very susceptible
to disease, which has decimated
shrimp populations across entire regions. Increasing ecological problems, repeated
disease outbreaks, and pressure and criticism from both NGOs and consumer countries led to changes in the industry in
the late 1990s and generally stronger regulations. In 1999, governments,
industry representatives, and environmental organizations initiated a program
aimed at developing and promoting more sustainable
farming
practices through the Seafood Watch program.
Freshwater
prawn farming
shares many characteristics with, including many problems with, marine shrimp farming. Unique problems are
introduced by the developmental life cycle of the main species, the giant river prawn.
The
global annual production of freshwater prawns (excluding crayfish and crabs) in 2003 was about 280,000 tonnes of which China
produced 180,000 tonnes followed by India and Thailand with 35,000 tonnes each.
Additionally, China produced about 370,000 tonnes of Chinese
river crab.
Molluscs
Aquacultured
shellfish include various oyster, mussel and clam species.
These bivalves are filter and/or deposit feeders, which rely on ambient primary
production rather than inputs of fish or other feed. As such shellfish
aquaculture is generally perceived as benign or even beneficial. Depending on the
species and local conditions, bivalve molluscs are either grown on the beach,
on longlines, or suspended from rafts and harvested by hand or by dredging. Abalone farming began in the
late 1950s and early 1960s in Japan and China. Since the mid-1990s,
this industry has become increasingly successful. Over-fishing and poaching have reduced wild
populations to the extent that farmed abalone now supplies most abalone meat.
Sustainably farmed molluscs can be certified by Seafood Watch and other
organizations, including the World
Wildlife Fund
(WWF). WWF initiated the "Aquaculture Dialogues" in 2004 to develop
measurable and performance-based standards for responsibly farmed seafood. In
2009, WWF co-founded the Aquaculture Stewardship Council (ASC) with the Dutch
Sustainable Trade Initiative (IDH) to manage the global standards and certification
programs.
Other groups
Other
groups include aquatic reptiles, amphibians, and miscellaneous invertebrates,
such as echinoderms and jellyfish. They are separately
graphed at the top right of this section, since they do not contribute enough
volume to show clearly on the main graph.
Commercially
harvested echinoderms include sea cucumbers and sea urchins. In China, sea cucumbers are farmed in
artificial ponds as large as 1,000 acres (400 ha).
Around the world
In
2004, the total world production of fisheries was 140 million tonnes of which aquaculture
contributed 45 million tonnes, about one third. The growth rate of
worldwide aquaculture has been sustained and rapid, averaging about 8 percent
per annum for over thirty years, while the take from wild fisheries has been essentially
flat for the last decade. The aquaculture market reached $86 billion in 2009.
Aquaculture
is an especially important economic activity in China. Between 1980 and 1997,
the Chinese Bureau of Fisheries reports, aquaculture harvests grew at an annual
rate of 16.7 percent, jumping from 1.9 million tonnes to nearly 23 million
tonnes. In 2005, China accounted for 70% of world production. Aquaculture is also
currently one of the fastest growing areas of food production in the U.S.
Approximately
90% of all U.S. shrimp consumption is farmed and imported. In recent years salmon aquaculture has
become a major export in southern Chile, especially in Puerto Montt, Chile's
fastest-growing city.
Over reporting
China
overwhelmingly dominates the world in reported aquaculture output. They report a total
output which is double that of the rest of the world put together. However,
there are issues with the accuracy of China's returns.
In
2001, the fisheries scientists Reg Watson and Daniel Pauly expressed concerns
in a letter to Nature, that China was over reporting its catch from wild
fisheries in the 1990s. They said that made
it appear that the global catch since 1988 was increasing annually by 300,000
tonnes, whereas it was really shrinking annually by 350,000 tonnes. Watson and
Pauly suggested this may be related to China policies where state entities that
monitor the economy are also tasked with increasing output. Also, until
recently, the promotion of Chinese officials was based on production increases
from their own areas.
China
disputes this claim. The official Xinhua
News Agency
quoted Yang Jian, director general of the Agriculture Ministry's Bureau of
Fisheries, as saying that China's figures were "basically correct".However, the FAO accepts there are issues with the
reliability of China's statistical returns, and currently treats data from
China, including the aquaculture data, apart from the rest of the world.
Methods
Mariculture
Mariculture is the term used for
the cultivation of marine organisms in seawater, usually in
sheltered coastal waters. In particular, the farming of marine fish is an
example of mariculture, and so also is the farming of marine crustaceans (such
as shrimps), molluscs (such as oysters) and seaweed.
Integrated
Integrated Multi-Trophic Aquaculture (IMTA) is a practice
in which the by-products (wastes) from one species are recycled to become inputs
(fertilizers, food) for another. Fed aquaculture (for
example, fish, shrimp) is combined with
inorganic extractive and organic extractive (for example, shellfish) aquaculture to
create balanced systems for environmental sustainability (biomitigation),
economic stability (product diversification and risk reduction) and social
acceptability (better management practices).
"Multi-Trophic"
refers to the incorporation of species from different trophic or nutritional levels in the same
system. This is one
potential distinction from the age-old practice of aquatic polyculture, which could simply
be the co-culture of different fish species from the same trophic level. In
this case, these organisms may all share the same biological and chemical processes,
with few synergistic benefits, which
could potentially lead to significant shifts in the ecosystem. Some traditional
polyculture systems may, in fact, incorporate a greater diversity of species,
occupying several niches, as extensive
cultures (low intensity, low management) within the same pond. The
"Integrated" in IMTA refers to the more intensive cultivation of the
different species in proximity of each other, connected by nutrient and energy
transfer through water.
Ideally,
the biological and chemical processes in an IMTA system should balance. This is
achieved through the appropriate selection and proportions of different species
providing different ecosystem functions. The co-cultured species are typically
more than just biofilters; they are
harvestable crops of commercial value. A working IMTA
system can result in greater total production based on mutual benefits to the
co-cultured species and improved ecosystem health, even if the
production of individual species is lower than in a monoculture over a short term
period.
Sometimes
the term "Integrated Aquaculture" is used to describe the integration
of monocultures through water transfer. For all intents and
purposes however, the terms "IMTA" and "integrated
aquaculture" differ only in their degree of descriptiveness. Aquaponics, fractionated
aquaculture, IAAS (integrated agriculture-aquaculture systems), IPUAS
(integrated peri-urban-aquaculture systems), and IFAS (integrated
fisheries-aquaculture systems) are other variations of the IMTA concept.
Netting materials
Various
materials, including nylon, polyester, polypropylene, polyethylene, plastic-coated
welded wire, rubber, patented rope products (Spectra, Thorn-D, Dyneema), galvanized steel and copper are used for netting
in aquaculture fish enclosures around the world. All of these
materials are selected for a variety of reasons, including design feasibility, material strength, cost, and corrosion
resistance.
Recently,
copper alloys have become important netting materials in aquaculture because
they are antimicrobial (i.e., they destroy bacteria, viruses, fungi, algae, and other microbes) and they therefore
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.
Issues
Aquaculture
can be more environmentally damaging than exploiting wild fisheries on a local area basis but has
considerably less impact on the global environment on a per kg of production
basis. Local concerns
include waste handling, side-effects of antibiotics, competition between
farmed and wild animals, and using other fish to feed more marketable carnivorous fish. However,
research and commercial feed improvements during the 1990s and 2000s have
lessened many of these concerns.
Aquaculture
may contribute to propagation of invasive species. As the cases of Nile perch and Janitor fish show, this issue may
be damaging to native fauna.
Fish
waste is organic and composed of nutrients necessary in all components of
aquatic food webs. In-ocean aquaculture often produces much higher than normal fish
waste concentrations. The waste collects on the ocean bottom, damaging or
eliminating bottom-dwelling life. Waste can also decrease dissolved oxygen levels in the water column, putting further
pressure on wild animals.
Fish oils
Tilapia
from aquaculture has been shown to contain more fat and a much higher ratio of
omega-6 to omega-3 oils.
Impacts on wild fish
Salmon
farming currently leads to a high demand for wild forage fish. Fish do not
actually produce omega-3 fatty acids, but instead accumulate them from either
consuming microalgae that produce these
fatty acids, as is the case with forage fish like herring and sardines, or, as is the case
with fatty predatory
fish,
like salmon, by eating prey
fish
that have accumulated omega-3
fatty acids
from microalgae. To satisfy this requirement, more than 50 percent of the world
fish oil production is fed to
farmed salmon.
In
addition, as carnivores, salmon require large nutritional intakes of protein,
protein which is often supplied to them in the form of forage fish. Consequently, farmed
salmon consume more wild
fish
than they generate as a final product. To produce one pound of farmed salmon,
products from several pounds of wild fish are fed to them. As the salmon
farming industry expands, it requires more wild forage fish for feed, at a time
when seventy five percent of the worlds monitored fisheries are already near to
or have exceeded their maximum sustainable yield. The industrial scale
extraction of wild forage fish for salmon farming then impacts the
survivability of the wild predator fish who rely on them for food.
Fish
can escape from coastal pens, where they can interbreed with their wild
counterparts, diluting wild genetic stocks. Escaped fish can
become invasive, out competing
native species.
Coastal ecosystems
Aquaculture
is becoming a significant threat to coastal ecosystems. About 20 percent of
mangrove forests have been destroyed since 1980, partly due to shrimp farming. An extended
cost–benefit analysis of the total
economic value
of shrimp aquaculture built on mangrove ecosystems found that the external costs were much
higher than the external benefits. Over four decades,
269,000 hectares (660,000 acres) of Indonesian mangroves have been converted to
shrimp farms. Most of these farms are abandoned within a decade because of the toxin build-up and nutrient loss.
Salmon
farms
are typically sited in pristine coastal ecosystems which they then pollute. A
farm with 200,000 salmon discharges more fecal waste than a city of 60,000
people. This waste is discharged directly into the surrounding aquatic
environment, untreated, often containing antibiotics and pesticides." There is also an
accumulation of heavy
metals
on the benthos (seafloor) near the
salmon farms, particularly copper and zinc.
Genetic modification
A
type of salmon have been genetically
modified
for faster growth, although it has not been approved for commercial use, due to
opposition. One study, in a
laboratory setting, found that modified salmon mixed with their wild relatives
were aggressive in competing, but ultimately failed.
Animal welfare
As
with the farming of terrestrial animals, social attitudes influence the need
for humane practices and regulations in farmed marine animals. Under the
guidelines advised by the Farm Animal Welfare Council good animal welfare
means both fitness and a sense of well being in the animal's physical and
mental state. This can be defined by the Five Freedoms:
- Freedom from hunger & thirst
- Freedom from discomfort
- Freedom from pain, disease, or injury
- Freedom to express normal behaviour
- Freedom from fear and distress
However,
the controversial issue in aquaculture is whether fish and farmed marine
invertebrates are actually sentient, or have the
perception and awareness to experience suffering. Although no evidence of this
has been found in marine invertebrates, recent studies
conclude that fish do have the necessary receptors (nociceptors) to sense noxious
stimuli and so are likely to experience states of pain, fear and stress. Consequently,
welfare in aquaculture is directed at vertebrates; finfish in particular.
Common welfare concerns
Welfare
in aquaculture can be impacted by a number of issues such as stocking
densities, behavioural interactions, disease and parasitism. A major problem in determining the
cause of impaired welfare is that these issues are often all interrelated and
influence each other at different times.
Optimal
stocking density is often defined by the carrying capacity of the stocked
environment and the amount of individual space needed by the fish, which is
very species specific. Although behavioural interactions such as shoaling may mean that high
stocking densities are beneficial to some species, in many cultured
species high stocking densities may be of concern. Crowding can constrain
normal swimming behaviour, as well as increase aggressive and competitive
behaviours such as cannibalism, feed competition, territoriality and
dominance/subordination hierarchies. This potentially increases
the risk of tissue damage due to abrasion from fish-to-fish contact or
fish-to-cage contact. Fish can suffer
reductions in food intake and food
conversion efficiency. In addition, high
stocking densities can result in water flow being insufficient, creating
inadequate oxygen supply and waste product removal. Dissolved oxygen is essential for
fish respiration and concentrations below critical levels can induce stress and
even lead to asphyxiation. Ammonia, a nitrogen
excretion product, is highly toxic to fish at accumulated levels, particularly
when oxygen concentrations are low.
Many
of these interactions and effects cause stress in the fish, which can be a
major factor in facilitating fish disease. For many parasites,
infestation depends on the host's degree of mobility, the density of the host
population and vulnerability of the host's defence system. Sea lice are the
primary parasitic problem for finfish in aquaculture, high numbers causing
widespread skin erosion and haemorrhaging, gill congestion,and increased mucus
production.
There are also a number of prominent viral and bacterial pathogens that can have severe effects on internal organs and nervous systems.
There are also a number of prominent viral and bacterial pathogens that can have severe effects on internal organs and nervous systems.
Improving welfare
The
key to improving welfare of marine cultured organisms is to reduce stress to a
minimum, as prolonged or repeated stress can cause a range of adverse effects.
Attempts to minimise stress can occur throughout the culture process. During
grow out it is important to keep stocking densities at appropriate levels
specific to each species, as well as separating size classes and grading to
reduce aggressive behavioural interactions. Keeping nets and cages clean can
assist positive water flow to reduce the risk of water degradation.
Not
surprisingly disease and parasitism can have a major effect on fish welfare and
it is important for farmers not only to manage infected stock but also to apply
disease prevention measures. However, prevention methods, such as vaccination,
can also induce stress because of the extra handling and injection. Other methods
include adding antibiotics to feed, adding chemicals into water for treatment
baths and biological control, such as using cleaner wrasse to remove lice from
farmed salmon.
Many
steps are involved in transport, including capture, food deprivation to reduce
faecal contamination of transport water, transfer to transport vehicle via nets
or pumps, plus transport and transfer to the delivery location. During
transport water needs to be maintained to a high quality, with regulated
temperature, sufficient oxygen and minimal waste products. In some cases anaesthetics may be used in small
doses to calm fish before transport.
Aquaculture
is sometimes part of an environmental rehabilitation program or as an aid in
conserving endangered species.
Prospects
Global
wild
fisheries
are in decline, with valuable habitat such as estuaries in critical
condition.The aquaculture or farming of piscivorous fish, like salmon, does not help the
problem because they need to eat products from other fish, such as fish meal and fish oil. Studies have shown
that salmon
farming
has major negative
impacts
on wild salmon, as well as the forage fish that need to be
caught to feed them. Fish that are higher
on the food
chain
are less efficient sources of food energy.
Apart
from fish and shrimp, some aquaculture undertakings, such as seaweed and
filter-feeding bivalve mollusks like oysters, clams, mussels and scallops, are relatively
benign and even environmentally restorative.Filter-feeders
filter pollutants as well as nutrients from the water, improving water quality. Seaweeds extract nutrients
such as inorganic nitrogen and phosphorus directly from the
water, and filter-feeding mollusks can extract
nutrients as they feed on particulates, such as phytoplankton and detritus.
Some
profitable aquaculture cooperatives promote sustainable practices. New methods lessen
the risk of biological and chemical pollution through minimizing
fish stress, fallowing netpens, and applying Integrated Pest Management. Vaccines are being used more
and more to reduce antibiotic use for disease
control.
Onshore
recirculating aquaculture systems, facilities using polyculture techniques, and
properly sited facilities (for example, offshore areas with strong currents)
are examples of ways to manage negative environmental effects.
Recirculating
aquaculture systems (RAS) recycle water by circulating it through filters to
remove fish waste and food and then recirculating it back into the tanks. This
saves water and the waste gathered can be used in compost or, in some cases,
could even be treated and used on land. While RAS was developed with freshwater
fish in mind, scientist have found a way to rear saltwater fish using RAS in
low-salinity waters.Although saltwater
fish are raised in off-shore cages or caught with nets in water that typically
has a salinity of 35 parts
per thousand
(ppt), scientists were able to produce healthy pompano, a saltwater fish, in
tanks with a salinity of only 5 ppt. Commercializing low-salinity RAS are
predicted to have positive environmental and economical effects. Unwanted
nutrients from the fish food would not be added to the ocean and the risk of
transmitting diseases between wild and farm-raised fish would greatly be
reduced. The price of expensive saltwater fish, such as the pompano and combia
used in the experiments, would be reduced. However, before any of this can be
done researchers must study every aspect of the fish's lifecycle, including the
amount of ammonia and nitrate the fish will tolerate in the water, what to feed
the fish during each stage of its lifecycle, the stocking rate that will produce
the healthiest fish, etc.
Some
16 countries now use geothermal energy for aquaculture,
including China, Israel, and the United
States. In California, for
example, 15 fish farms produce tilapia, bass, and catfish with warm water from
underground. This warmer water enables fish to grow all year round and mature
more quickly. Collectively these California farms produce 4.5 million kilograms
of fish each year.
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