Oysters-Shellfish Farming

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Oysters: Shellfish Farming
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Ian Laing, Centre for Environment Fisheries and Aquaculture Science, Weymouth, United Kingdom
Justin J Bopp, Stony Brook University, Stony Brook, NY, United States
© 2018 Elsevier Inc. All rights reserved.
A Long History 1
A Healthy Food 1
The Oyster 2
Current Status 2
General Biology 2
Methods of Cultivation—Seed Supply 3
Wild Larvae Collection 3
Hatcheries 3
Ponds 5
Methods of Cultivation—On-Growing 5
Standards 7
Pearl Oysters 7
Site Selection for On-Growing 9
Risks 9
Pollutants 9
Predators 9
Competitors 10
Diseases 10
Fouling 10
Toxic Algae 10
Stock Enhancement 10
Nonnative Species 11
Food Safety 11
Recent Developments 12
References 12
Further Reading 12
As I ate the oysters with their strong taste of the sea and their faint metallic taste that the cold white wine washed away, leaving only the sea taste and the succulent
texture, and as I drank their cold liquid from each shell and washed it down with the crisp taste of the wine, I lost the empty feeling and began to be happy and to make
plans. (Ernest Hemingway in A Moveable Feast).
A Long History
Oysters have been prized as a food for millennia. Carbon dating of shell deposits in middens in Australia show that the aborigines
took the Sydney rock oyster for consumption in around 6000 BC. Oyster farming, nowadays carried out all over the world, has a very
long history, although there are various thoughts as to when it first started. It is generally believed that the ancient Romans and the
Greeks were the first to cultivate oysters, but some maintain that artificial oyster beds existed in China long before this.
It is said that the ancient Chinese raised oysters in specially constructed ponds. The Romans harvested immature oysters and
transferred them to an environment more favorable to their growth. Greek fishermen would toss broken pottery dishes onto natural
oyster beds to encourage the spat to settle.
All of these different cultivation methods are still practiced in a similar form today.
A Healthy Food
Oysters (Fig. 1) have been an important food source since Neolithic times and are one of the most nutritionally well balanced of
foods. They are ideal for inclusion in low-cholesterol diets. They are high in omega-3 fatty acids and are an excellent source of
vitamins. Four or five medium-size oysters supply the recommended daily allowance of a whole range of minerals.
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Change History: June 2018. J. Bopp added keywords, updated the text, Fig. 2, Table 1, further reading, and added the section on Recent Developments. I Laing
updated Current Status, an abstract, Table 1 and Fig. 2, Relevant Websites, and Nonnative Species and Pearl Oysters sections, and added new section on
Standards.
Encyclopedia of Ocean Sciences, 3rd Edition https://doi.org/10.1016/B978-0-12-409548-9.04269-X 1

The Oyster
Oysters are one among a number of bivalve mollusks that are cultivated. Others include clams, cockles, mussels, and scallops.
Current Status
Oysters form the fourth most important group, by volume, after cyprinid fishes, seaweeds and clams, in world aquaculture
production. In 2015, 600 thousand metric tonnes were produced (Food and Agriculture Organization (FAO) data). Asia and the
Pacific region produce 93.8% of this total production.
The FAO of the United Nations lists 15 categories of cultivated oyster species. The cupped oysters, especially the Pacific oyster
(Crassostrea gigas) are by far the most important. Annual production of these species is 72.7% of the 600 thousand metric tonnes of
global oyster production, worth US $1.1 billion (see Table 1).
The yield from wild oyster fisheries is small compared with that from farming and has declined steadily in recent years. It has
fallen from over 300,000 tons in 1980 to 135,000 tons in 2016. The rapid growth in Pacific oyster production from aquaculture in
the mid 1970s has slowed in recent years (see Fig. 2).
General Biology
As might be expected, given a long history of cultivation, there is a considerable amount known about the biology of oysters.
The shell of bivalves is in two halves, or valves. Two muscles, called adductors, run between the inner surfaces of the two valves
and can contract rapidly to close the shell tightly. When exposed to the air, during the tidal cycle, oysters close tightly to prevent
desiccation of the internal tissues. They can respire anaerobically (i.e., without oxygen) when out of water but have to expel toxic
metabolites when reimmersed as the tide comes in. They are known to be able to survive for long periods out of water at low
temperatures such as those used for storage after collection.
Within the shell is a fleshy layer of tissue called the mantle; there is a cavity (the mantle cavity) between the mantle and the body
wall proper. The mantle secretes the layers of the shell, including the inner nacreous, or pearly, layer. Oysters respire by using both
gills and mantle. The gills, suspended within the mantle cavity, are large and function in food gathering (filter feeding) as well as in
Fig. 1 A dish of Pacific oysters.
Table 1 The four most important cupped oyster species produced worldwide
Tonnages are 2015 figures (FAO data)
Oyster species Number of producing countries Major producing countries (% of total) Production (metric tonnes)
Pacific oyster 26 Korea (47), Japan (27), France (11), USA (6) 4,340,204
American oyster 3 USA (73), Mexico (24), Canada (3) 111,742
Slipper oyster 1 Philippines (100) 22,525
Mangrove oyster 3 Cuba (97), Dominican Republic (2) 1650
FAO statistics for oyster production in China were unavailable.
2Oysters: Shellfish Farming

respiration. As water passes over the gills, organic particulate material, especially phytoplankton, is strained out and is carried to the
mouth.
Oysters have separate sexes, but they may change sex one or more times during their life span, being true hermaphrodites. In
most species, the eggs and sperm are shed directly into the water where fertilization occurs. Larvae are thus formed and these swim
and drift in the water, feeding on natural phytoplankton. After 2–3 weeks, depending on local environmental conditions, the larvae
are mature and they develop a foot. At this stage they sink to the seabed and explore the sediment surface until they find a suitable
surface on which to settle and attach permanently, by cementation. Next, they go through a series of morphological and
physiological changes, a process known as metamorphosis, to become immature adults. These are called juveniles, spat, or seed.
Cultivated species of flat oysters brood the young larvae within the mantle cavity, releasing them when they are almost ready to
settle. Fecundity is usually related to age, with older and larger females producing many more larvae.
Growth of juveniles is usually quite rapid initially, before slowing down in later years. The length of time that oysters take to
reach a marketable size varies considerably, depending on local environmental conditions, particularly temperature and food
availability. Pacific oysters may reach a market size of 70–100 g live weight (shell-on) in 18–30 months.
Methods of Cultivation—Seed Supply
Oyster farming is dependent on a regular supply of small juvenile animals for growing on to market size. These can be obtained
primarily in one of two ways, either from naturally occurring larvae in the plankton or artificially, in hatcheries.
Wild Larvae Collection
Most oyster farmers obtain their seed by collecting wild set larvae. Special collection materials, generically known as “cultch,”are
placed out when large numbers of larvae appear in the plankton. Monitoring of larval activity is helpful to determine where and
when to put out the cultch. It can be difficult to discriminate between different types of bivalve larvae in the plankton to ensure that
it is the required species that is present but recently, modern highly sensitive molecular methods have been developed for this.
Various materials can be used for collection. Spat collected in this way are often then thinned prior to growing on (Fig. 3). In
China, coir rope is widely used, as well as straw rope, flax rope, and ropes woven by thin bamboo strips. Shells, broken tiles,
bamboo, hardwood sticks, plastics, and even old tires can also be used. Coatings are sometimes applied.
Hatcheries
Restricted by natural conditions, the amount of wild spat collected may vary from year to year. Also, where nonnative oyster species
are cultivated, there may be no wild larvae available. In these circumstances, hatchery cultivation is necessary. This also allows for
genetic manipulation of stocks, to rear and maintain lines specifically adapted for certain traits. Important traits for genetic
improvement include growth rate, environmental tolerances, disease resistance, and shell shape.
Methods of cryopreservation of larvae are being developed and these will contribute to maintaining genetic lines. Furthermore,
triploid oysters, with an extra set of chromosomes, can only be produced in hatcheries. These oysters often have the advantage of
better growth and condition, and therefore marketability, during the summer months, as gonad development is inhibited.
Techniques for hatchery rearing were first developed in the 1950s and today follow well-established procedures.
Adult broodstock oysters are obtained from the wild or from held stocks. Depending on the time of year, these may need to be
bought into fertile condition by providing a combination of elevated temperature and food (cultivated phytoplankton diets) over
several weeks (see Fig. 4). Selection of the appropriate broodstock conditioning diet is very important. An advantage of hatchery
Fig. 2 World aquaculture production, in metric tonnes, of Pacific oysters (1950–2016). Aquaculture production was not available for China.
Oysters: Shellfish Farming 3

production is that it allows for early season production in colder climates and this ensures that seeds have a maximum growing
period prior to their first overwintering.
For cultivated oyster species, mature gametes are usually physically removed from the gonads. This involves sacrificing some ripe
adults. Either the gonad can be cut repeatedly with a scalpel and the gametes washed out with filtered seawater into a part-filled
container, or a clean Pasteur pipette can be inserted into the gonad and the gametes removed by exerting gentle suction.
Broodstock can also be induced to spawn. Various stimuli can be applied. The most successful methods are those that are natural
and minimize stress. These include temporary exposure to air and thermal cycling (alternative elevated and lowered water
temperatures). Serotonin and other chemical triggers can also be used to initiate spawning but these methods are not generally
recommended as eggs liberated using such methods are often less viable.
Flat oysters, of the genera Ostrea and Tiostrea, do not need to be stimulated to spawn. They will spawn of their own accord during
the conditioning process as they brood larvae within their mantle cavities for varying periods of time depending on species and
temperature.
The fertilized eggs are then allowed to develop to the fully shelled D-larva veliger stage, so called because of the characteristic “D”
shape of the shell valves (Fig. 5).
These larvae are then maintained in bins with gentle aeration. Static water is generally used and this is exchanged daily or once
every 2 days. Through-flow systems, with meshes to prevent loss of larvae, are also employed. Cultured microalgae are added into
the tanks several times per day, at an appropriate daily ration according to the number and size of the larvae.
The larvae eventually become competent to settle and for this, surfaces must be provided. The area of settlement surface is
important. Types of materials in common usage to provide large surface areas for settlement include sheets of slightly roughened
Fig. 3 A demonstration of the range of oyster spat collectors used in France.
Fig. 4 The SeaCAPS continuous culture system for algae. An essential element for a successful oyster hatchery is the means to cultivate large quantities of marine
micro algae (phytoplankton) food species.
4Oysters: Shellfish Farming

polyvinyl chloride (PVC), layers of shell chips and particles prepared by grinding aged, clean oyster shell spread over the base of
settlement trays or tanks, bundles, bags, or strings of aged clean oyster shells dispersed throughout the water column, usually in
settlement tanks or various plastic or ceramic materials coated with cement (lime/mortar mix).
For some of these methods, the oysters are subsequently removed from the settlement surface to produce “cultchless”spat. These
can then be grown as separate individuals through to marketable size and sold as whole or half shell, usually live.
Provision of competence to settle Pacific oyster larvae for remote setting at oyster farms is common practice on the Pacific coast
of North America. Hatcheries provide the mature larvae and the farmers themselves set them and grow the spat for seeding oyster
beds or in suspended culture.
In other parts of the world, hatcheries set the larvae, as described above, and grow the spat to a size that growers are able to
handle and grow.
Oyster juveniles from hatchery-reared larvae perform well in standard pumped upwelling systems and survival is usually good,
although some early losses may occur immediately following metamorphosis. Diet, ration, stocking density, and water flow rate are
all important in these systems (Fig. 6). They are only suitable for initial rearing of small seed. As the spat grow, food is increasingly
likely to become limiting in these systems and they must be transferred to the sea for on-growing.
The size at which spat is supplied is largely dictated by the requirements and maturity of the grow-out industry. Seed native
oysters are made available from commercial hatcheries at a range of sizes up to 25–30 mm. The larger the seed, the more expensive
they are but this is offset by the higher survival rate of larger seed. Larger seed should also be more tolerant to handling.
Ponds
Pond culture offers a third method to provide seed. This was the method that was originally developed in Europe in early attempts
to stimulate production following the decline of native oyster stocks in the late nineteenth century. Ponds of 1–10 ha in area and
1–3 m deep were built near to high water spring tides, filled with seawater, and then isolated for the period of time during which the
oysters are breeding naturally, usually May–July. Collectors put into the ponds encourage and collect the settlement of juvenile
oysters. There is an inherent limited amount of control over the process and success is very variable. In France, where spat collectors
were also deployed in the natural environment, it was relatively successful and became an established method for a time. In the UK,
spat production from ponds built in the early 1900s was insufficiently regular to provide a reliable supply of seed to the industry
and the method was largely abandoned in the middle of the twentieth century in favor of the more controlled conditions available
in hatcheries.
Methods of Cultivation—On-Growing
Various methods are available for on-growing oyster seed once this has been obtained, from either wild set larvae, hatcheries, or
ponds.
Oysters smaller than 10 g need to be held in trays or bags attached to a superstructure on the foreshore until they are large
enough to be put directly on to the substrate and be safe from predators, strong tidal and wave action, or siltation (Fig. 7).
Tray cultivation of oysters can be successful in water of minimal flow, where water exchange is driven only by the rise and fall of
the tide and gentle wave action. In such circumstances it may even be possible in open baskets.
In more exposed sites, systems developed in Australia and employing plastic mesh baskets attached to or suspended from wires
(see Fig. 8) are becoming increasingly popular. It is claimed that an oyster with a better shape, free from worm (Polydora) infestation,
will result from using these systems. Polydora can cause unsightly brown blemishes on the inner surface of the shell and decrease
marketability of the stock. Less labor is required with these systems but they are more expensive to purchase initially.
Fig. 5 Pacific oyster D larvae. At this stage shell length is about 70 mm.
Oysters: Shellfish Farming 5

Fig. 6 Indoor (A) and outdoor (B) oyster nursery system, in which seawater and algae food are pumped up through cylinders fitted with mesh bases and containing
the seed.
Fig. 7 The traditional bag and trestle method for on-growing Pacific oysters.
6Oysters: Shellfish Farming

In all of the above systems, the mesh size can be increased as the oysters grow, to improve the flow of water and food through the
animals.
Holding seed oysters in trays or attached to the cultch material onto which they were settled, and suspended from rafts,
pontoons, or long lines is an alternative method in locations where current speed will allow. The oysters should grow more quickly
because they are permanently submerged but the shell may be thinner and therefore more susceptible to damage. Early stages of
predator species such as crabs and starfish can settle inside containers, where they can cause significant damage unless containers are
opened and checked on a regular basis. In the longer term the oysters will perform better on the seabed, although they can be reared
to market size in the containers.
Protective fences can be put up around ground plots to give some degree of protection to smaller oysters from shore crabs.
Potting crabs in the area of the lays is another method of control. The steps in the oyster cultivation process are shown as a diagram
in Fig. 9.
The correct stocking density is important so as not to exceed the carrying capacity of a body of water. When carrying capacity is
exceeded, the algal population in the water is insufficient and growth declines. Mortalities also sometimes occur. Yields in
extensively cultivated areas are usually about 25 ton per hectare per year but this can increase to 70 ton where individual plots
are well separated.
In France, premium quality oysters are sometimes finished by holding them in fattening ponds known as claires (see Fig. 10), in
which a certain type of algae is encouraged to bloom, giving a distinctive green color to the flesh.
In the UK, part-grown native flat oysters from a wild fishery are relayed in spring into areas in which conditions are favorable to
give an increase in meat yield over a period of a few months, prior to marketing in the winter.
Standards
The FAO published guidelines for aquaculture certification in 2011. Standards for organic certification of mollusk cultivation have
been developed by the Aquaculture Stewardship Council and general aquaculture standards by Global G.A.P. Many oyster growers
consider that the process is intrinsically organic.
Pearl Oysters
There is an important component of the oyster farming industry, located in various countries in the Pacific region, including Japan,
Australia, Vietnam, Indonesia and the Philippines, devoted to the production of pearls. The process involves inserting into the oyster
a nucleus, made with shell taken from a North American mussel, and a tiny piece of mantle cut from another oyster. The oysters are
cultivated in carefully tended suspended systems while pearls develop around the nucleus. Once the pearls have been taken out of
the oysters, they are seeded anew. A healthy oyster can be reseeded as many as four times with a new nucleus. As the oyster grows, it
can accommodate progressively bigger pearl nuclei. Therefore, the biggest pearls are most likely to come from the oldest oysters.
Fig. 8 Open baskets for on-growing, as developed in Tasmania for Pacific oysters.
Oysters: Shellfish Farming 7

Adult oysters in the sea
Immature Mature
Brood stock
conditioning
Hatchery
Larvae
Spat
Spat
Spawn
in wild
Larvae
Spat
Ponds
On-growing
in the sea
(spat to
adults)
On cultch
In trays
On-bottom
Adult oysters for
the market
Remove
from
cultch
Adult oysters for
the market
Collect spat
on
settlement
material
(cultch)
Nursery
Spat
Fig. 9 The steps and processes of oyster farming.
Fig. 10 Oyster fattening ponds, or Claires, in France.
8Oysters: Shellfish Farming

Site Selection for On-Growing
A range of physical, biological, and chemical factors will influence survival and growth of oysters. Many of these factors are subject
to seasonal and annual variation and prospective oyster farmers are usually advised to monitor the conditions and to see how well
oysters grow and survive at their chosen site for at least a year before any commercial culture begins.
Seawater temperature has a major effect on seasonal growth and may be largely responsible for any differences in growth
between sites. Changes in salinity do not affect the growth of bivalves by as much as variation in temperature. However, most
bivalves will usually only feed at higher salinities. Pacific oysters prefer salinity levels nearer to 25 psu, conditions typical of many
estuaries and inshore waters.
Growth rates are strongly influenced by the length of time during which the animals are covered by the tide. Growth of oysters in
trays stops when they are exposed to air for more than about 35% of the time. However, this fact can be used to advantage by the
cultivator who may wish, for commercial reasons, to slow down or temporarily stop the growth of the stock. This can be achieved by
moving the stock higher up the beach. It is a practice that is routinely adopted in Korea and Japan for “hardening off”wild-caught
spat prior to sale.
Other considerations are related to access and harvesting. It is important to consider the type of equipment likely to be used for
planting, maintenance, and harvesting, particularly at intertidal sites. Some beaches will support wheeled or tracked vehicles, while
others are too soft and will require the use of a boat to transport equipment.
Risks
Oyster farming can be at risk from pollutants, predators, competitors, diseases, fouling organisms, and toxic algae species.
Pollutants
Some pollutants can be harmful to oysters at very low concentrations. During the 1980s, it was found that tributyl tin (TBT), a
component of marine antifouling paints, was highly toxic to bivalve mollusks at extremely low concentrations in the seawater.
Pacific oysters cultivated in areas in which large numbers of small vessels were moored showed stunted growth and thickening of the
shell, and natural populations of flat oysters failed to breed (see Fig. 11). The use of this compound on small vessels was widely
banned in the late 1980s, and since then the oyster industry has recovered. The International Maritime Organization has since
announced a ban for larger vessels as well. When marketed for consumption, oysters must meet a number of “end product”
standards. These include a requirement that the shellfish should not contain toxic or objectionable compounds such as trace metals,
organochlorine compounds, hydrocarbons, and polycyclic aromatic hydrocarbons (PAHs) in such quantities that the calculated
dietary intake exceeds the permissible daily amount.
Predators
In some areas oyster drills or tingles, which are marine snails that eat bivalves by rasping a hole through the shell to gain access to the
flesh, are a major problem.
Fig. 11 Compared with a normal shell (upper shell section), TBT from marine antifouling paints causes considerable thickening of Pacific oyster shells (lower
section). These compounds are now banned.
Oysters: Shellfish Farming 9

Competitors
Competitors include organisms such as slipper limpets (Crepidula fornicata), which compete for food and space. In silt laden waters,
they also produce a muddy substrate, which is unsuitable for cultivation. They can be a significant problem. An example is around
the coast of Brittany, where slipper limpets have proliferated in the native flat oyster areas during the last 30 years. In order to try to
control this problem, approximately 40,000–50,000 ton of slipper limpets are harvested per year. These are taken to a factory where
they are converted to a calcareous fertilizer.
Diseases
The World Organisation for Animal Health (OIE) lists seven notifiable diseases of mollusks and six of these can infect at least one of
the cultivated oyster species. Some of these diseases, often spread through national and international trade, have had a devastating
effect on oyster stocks worldwide. For example, Bonamia, a disease caused by the protist parasitic organism Bonamia ostreae, has had
a significant negative impact on Ostrea edulis production throughout its distribution range in Europe. Mortality rates in excess of
80% have been noted. The effect this can have on yields can be seen in the drastic (93%) drop in recorded production in France,
from 20,000 ton per year in the early 1970s to 1400 ton in 1982. A major factor in the introduction and success of the Pacific oyster
as a cultivated species has been that it is resistant to major diseases, although it is not completely immune to all problems.
There are reports of summer mortality episodes, especially in Europe and the USA, and infections by a herpes-like virus have
been implicated in some of these. Vibrio bacteria are also associated with larval mortality in hatcheries.
The Fisheries and Oceans Canada website lists 53 diseases and pathogens of oysters. Juvenile oyster disease is a significant
problem in cultivated Crassostrea virginica in the Northeastern United States. It is thought to be caused by a bacterium (Roseovarius
crassostreae).
Fouling
Typical fouling organisms include various seaweeds, sea squirts, tubeworms, and barnacles. The type and degree of fouling varies
with locality. The main effect is to reduce the flow of water and therefore the supply of food to bivalves cultivated in trays or on ropes
and to increase the weight and drag on floating installations. Fouling organisms grow in response to the same environmental factors
as are desirable for good growth and survival of the cultivated stock, so this is a problem that must be controlled rather than
avoided.
Toxic Algae
Mortalities of some marine invertebrates, including bivalves, have been associated with blooms of some alga species, including
Gyrodinium aureolum and Karenia mikimoto. These so-called red tides cause seawater discoloration and mortalities of marine
organisms. They have no impact on human health.
Stock Enhancement
If we accept the FAO definition of aquaculture as “The farming of aquatic organisms in inland and coastal areas, involving
intervention in the rearing process to enhance production and the individual or corporate ownership of the stock being
cultivated,”then in many cases stock enhancement can be included as a type of oyster farming.
Natural beds can be managed to encourage the settlement of juvenile oysters and sustain a fishery. Beds can be raked and tilled
on a regular basis to remove silt and ensure that suitable substrates are available for the attachment of the juvenile stages. Adding
settlement material (cultch) is also beneficial.
In some areas of the world, there has been a dramatic reduction in stocks of the native oyster species. This is attributed mainly to
overexploitation, although disease is also implicated. Native oyster beds form a biotope, with many associated epifaunal and
infaunal species. Loss of this habitat has resulted in a major decline in species richness in the coastal environment.
Considerable effort has been put into restoring these beds, using techniques that might fall under the definition of oyster
farming. A good example is the Chesapeake Bay Program for the native American oyster Crassostrea virginica. Overfishing followed
by the introduction of two protozoan diseases, believed to be inadvertently introduced to the Chesapeake through the importation
of a non-native oyster, Crassostrea gigas, in the 1930s, has combined to reduce oyster populations throughout Chesapeake Bay to
about 1% of historical levels. The Chesapeake Bay Program is committed to the restoration and creation of aquatic reefs. A key
component of the strategy to restore oysters is to designate sanctuaries, that is, areas where shellfish cannot be harvested. It is often
necessary within a sanctuary to rehabilitate the bottom to make it a suitable oyster habitat. Within sanctuaries aquatic reefs are
created primarily with oyster shell, the preferred substrate of spat. Alternative materials including concrete and porcelain are also
used. These permanent sanctuaries will allow for the development and protection of large oysters and therefore more fecund and
potentially disease-resistant oysters. Furthermore, attempts have been made at seeding with disease-free hatchery oysters.
10 Oysters: Shellfish Farming

Nonnative Species
The International Council for the Exploration of the Sea (ICES) Code of Practice sets forth recommended procedures and practices
to diminish the risks of detrimental effects from the intentional introduction and transfer of marine organisms. The Pacific oyster,
originally from Asia, has been introduced around the world and has become invasive in parts of Australia and New Zealand,
displacing the native rock oyster in some areas. It is also increasingly becoming a problem in northern European coastal regions. In
parts of France naturally recruited stock is competing with cultivated stock and has to be controlled.
The possibility of farming the nonnative Suminoe oyster (Crassostrea ariakensis) to restore oyster stocks in Chesapeake Bay was
thoroughly examined and eventually rejected due to concerns of potential harmful effects on the local ecology.
It should also be noted that aquaculture has been responsible for the introduction of a whole range of passenger species,
including pest species such as the slipper limpet and oyster drills, throughout the world.
Food Safety
Bivalve mollusks filter phytoplankton from the seawater during feeding; they also take in other small particles, such as organic
detritus, bacteria, and viruses. Some of these bacteria and viruses, especially those originating from sewage outfalls, can cause
serious illnesses in human consumers if they remain in the bivalve when it is eaten. The stock must be purified of any fecal bacterial
content in cleansing (depuration) tanks (Fig. 12) before sale for consumption. There are regulations governing this, which are based
on the level of contamination of the mollusks.
Viruses are not all removed by normal depuration processes and they can cause illness if the bivalves are eaten raw or only lightly
cooked, as oysters often are. These viruses can only be detected by using sophisticated equipment and techniques, although research
is being carried out to develop simpler methods.
Finally, certain types of naturally occurring algae produce toxins, which can accumulate in the flesh of oysters. People eating
shellfish containing these toxins can become ill and in exceptional cases death can result. Cooking does not denature the toxins
responsible nor does cleansing the shellfish in depuration tanks eliminate them. The risks to consumers are usually minimized by a
requirement for samples to be tested regularly. If the amount of toxin exceeds a certain threshold, the marketing of shellfish for
consumption is prohibited until the amount falls to a safe level.
Fig. 12 A stacked depuration system, suitable for cleansing oysters of microbiological contaminants. The oysters are held in trays in a cascade of UV-sterilized
water.
Oysters: Shellfish Farming 11

Recent Developments
From the most recent available FAO data (2016), oysters comprised 15.1% of global shellfish production. From 2010 to 2016
alone, global oyster aquaculture production increased by 25.1% coupled with a subsequent 60% increase in market value (USD)
(FAO, 2016). As a result of the expanding oyster aquaculture market, interest for managing this mollusk group sustainably while
optimizing production capacity has increased in recent years. However, concerns around the viability of shellfish aquaculture
operations have also been raised in the face of climate change projections and the increased prevalence of densely cultivated stocks
(Holmer, 2010). Thus, the formulation of robust prediction tools that incorporate the effects of environmental conditions on oyster
physiology and reproduction is necessary to enhance future management strategies. Within the past decade, the implementation of
complex mathematical models, such as Dynamic Energy Budget (DEB) models, have increased considerably for predicting oyster
population dynamics under variable environmental conditions through space and time (Filgueira et al., 2014;Thomas et al., 2016).
DEB theory describes ecological factors influencing organism physiology, life history characteristics, and is commonly used to
quantify energy flow allocation metrics including: assimilation, metabolism, food uptake, and reproduction (Kooijman, 2010;Scott
et al., 2013).
DEB models have become quite a ubiquitous tool for predicting the oyster growth under a variety of environmental conditions
and has transcended beyond standard DEB theory approaches. Standard DEB models incorporate food availability and temperature
as forcing variables, and prior knowledge regarding the physiology is required of the organism to improve parameter accuracy
(Lavaud et al., 2017). However, the inclusion of additional ecological forcing variables has gained attention to more rigorously
understand complex environmental impacts on oyster viability, especially in dynamic regions, such as estuaries. For instance, more
complex DEB models have revealed that eastern oyster biomass loss is highly correlated with temperature, but not salinity, under
limited food provisions, presumably a function of increased energy allocation towards respiration compared to growth (Lavaud
et al., 2017). Moreover, simulations of predicted climate change impacts, such as increased phytoplankton production and sea
surface temperature, on oyster physiology has been coupled with DEB model applications to provide a generic framework that can
potentially be used by oyster aquaculture managers (Thomas et al., 2016). Overall, the versatility and capability of incorporating
multiple environmental stressors in DEB models serves as a potentially robust tool for predicting oyster performance in farming
operations (Lavaud et al., 2017).
References
FAO (2016) Food and Agriculture Organization, Fisheries and Aquaculture Information and Statistical Service. http://www.fao.org/fishery/statistics/global-pro duction/query/en.
Filgueira R, Guyondet T, Comeau LA, and Grant J (2014) A fully-spatial ecosystem-DEB model of oyster (Crassostrea virginica) carrying capacity in the Richibucto Estuary, Eastern
Canada. Journal of Marine Systems 136: 42–54.
Holmer M (2010) Environmental issues of fish farming in offshore waters: Perspectives, concerns and research needs. Aquaculture Environment Interactions 1(1): 57–70.
Kooijman SALM (2010) Dynamic energy budget theory for metabolic organisation. New York, NY: Cambridge University Press.
Lavaud R, La Peyre MK, Casas SM, Bacher C, and La Peyre JF (2017) Integrating the effects of salinity on the physiology of the eastern oyster, Crassostrea virginica, in the northern
Gulf of Mexico through a Dynamic Energy Budget model. Ecological Modelling 363: 221–233.
Scott E, Hoyle A, and Shankland C (2013) PEPAd oysters: Converting dynamic energy budget models to bio-PEPA illustrated by a Pacific oyster case study. Electronic Notes in
Theoretical Computer Science 296: 211–228.
Thomas Y, Pouvreau S, Alunno-Bruscia M, Barillé L, Gohin F, Bryère P, and Gernez P (2016) Global change and climate-driven invasion of the Pacific oyster (Crassostrea gigas) along
European coasts: A bioenergetics modelling approach. Journal of Biogeography 43(3): 568–579.
Further Reading
Algal RA (2005) Algal culturing techniques. New York: Academic Press.
Austin B (2012) Infectious disease in aquaculture: prevention and control. Philadelphia: Woodhead Publishing.
P. Bueno, A. Lovatelli, H.P.C. Shetty. Pearl oyster farming and pearl culture, Regional Seafarming Development and Demonstration Project. (1991) FAO Rome FAO Project
Report No. 8.
Dore I (1991) Shellfish—A guide to oysters, mussels, scallops, clams and similar products for the commercial user. London: Springer.
Gosling E (2003) Bivalve mollusks: Biology, ecology and culture. London: Blackwell.
Helm MM, Bourne N, and Lovatelli A (2004) Hatchery culture of bivalves: A practical manual. FAO Rome FAO Fisheries Technical Paper 471.
Huguenin JE and Colt J (2002) Design and operating guide for aquaculture seawater systems, 2nd edn. Amsterdam: Elsevier.
Lavens P and Sorgeloos P (1996) Manual on the production and use of live food for aquaculture. FAO Fisheries Technical Paper 361.
Mann R (1979) Exotic species in mariculture. In: Proceedings of symposium on exotic species in mariculture: Case histories of the Japanese oyster, Crassostrea gigas (Thunberg),
with implications for other fisheries, Woods Hole, MA: Woods Hole Oceanographic Institution, Cambridge Press.
Matthiessen G (2001) Fishing news books series: Oyster culture. New York: Blackwell.
Shumway SE (2011) Shellfish aquaculture and the environment. Oxford: John Wiley & Sons.
Spencer BE (2002) Molluscan shellfish farming. New York: Blackwell.
12 Oysters: Shellfish Farming

Relevant Websites
http://www.cefas.co.uk—The online magazine “Shellfish News,”although produced primarily for the UK industry, has articles of general interest on oyster farming. It can be found on
the Publications and Data area of the Cefas web site. A booklet on site selection for bivalve cultivation is also available at this site.
http://www.crlcefas.org—Cefas is the EU community reference laboratory for bacteriological and viral contamination of oysters.
http://www.fao.org—There is a great deal of information on oyster farming throughout the world on the website of The Food and Agriculture Organization of the United Nations (FAO).
This website has statistics on oyster production, datasheets for various cultivated species, including Pacific oysters, and guidelines for aquaculture certification. The FAO also
publishes online manuals on: The production and use of live food for aquaculture (FAO Fisheries Technical Paper 361); Hatchery culture of bivalves (FAO Fisheries Technical Paper.
No. 471); Pearl oyster farming and pearl culture (FAO Project Report No. 8).
http://www.oie.int—Definitive information on oyster diseases can be found on the website of The World Organisation for Animal Health (OIE).
http://www.oysterworldcongress2012.com/—Copies of presentations at this first meeting of the Oyster World Congress in Arcachon, France are available on the web site. Included are
accounts of oyster farming in various countries.
http://www.pac.dfo-mpo.gc.ca—Further information on diseases can be found on the Fisheries and Oceans Canada website.
http://www.vims.edu—The Virginia Institute of Marine Science has information on oyster genetics and breeding programs and the background to the proposals to introduce the non-
native Crassostrea ariakensis to Chesapeake Bay.
http://www.was.org—The World Aquaculture Society website has a comprehensive set of links to other relevant web sites, including many national shellfish associations.
http://www.worldoyster.org/index_e.html—The World Oyster Society (WOS) is a membership organization established in 2005. It hosts International Symposia. There are links to the
proceedings and copies of some of the presentations from these meetings on the web site.
Oysters: Shellfish Farming 13