Crassostrea Virginica“Eastern oyster”,”American cupped oyster”, “Atlantic

oyster”, “Virginia oyster”

most closely related to the Eastern oyster

Economic Importance, Market Price, Market Locations, Country

• important both economically and ecologically. – filter estuarine waters– most economically important group of molluscs in the U.S.

• Last year market price avg was 8.50-10 per shucked lb

• The 5-year average price of Gulf Coast oysters (from 2006-2010) was $3.17/pound (in shell) (on bottom)• versus the same 5-year average price of New England oysters of $33.67/pound. (off-bottom)

• Harvests are a fraction of those of a century ago because of over-fishing, habitat destruction, pollution, and disease. • Naturally

– Gulf of St. Lawrence in Canada– Gulf of Mexico– Caribbean– Brazil – Argentina

• Introduced – on the west coast of North America– other areas of the world

• In recent years the total US harvest of oysters has been 30 million pounds of meatsabout 75% of the total is the eastern oyster. About 18 million pounds of total oyster production (all species) is by cultivation https://srac.tamu.edu/index.cfm/getFactSheet/whichfactsheet/92/)

Life Cycle and Larval Stages• Many bivalves will mature in their first year of life as

males. As they age, year by year, an increasing percentage may switch sex and become females.(Most oysters less than one year old are male, while most older oysters are female ) While some females can change back to males. This is known as protandric hermaphroditism.

• Spawns in early summer when water temperatures rise

• Adults simultaneously release eggs and sperm into the water column where fertilization occurs. (rising temps trigger sperm release from the first oyster which triggers those next to it and so on) Females can produce about 100 million eggs each year

• After spawning, oysters are thin because they have used up their stored food reserves. Adults grow larger and stronger as the weather cools

• In less than 24 hours, fertilized eggs develop into free-swimming larvae. Over the next two to three weeks, oyster larvae grow a "foot," which is used to crawl over and explore a surface before settling

• Once larvae find a suitable surface (cultch) to settle on, they secrete a cement-like substance, which fixes the left valve into place. Settled juvenile oysters are called "spat”

non-feeding microscopic swimming

Released simultaneouslyTo be fertilized in water column

24 to 48 hours

Growth to harvestable size (3 inches, 75mm) can take 12 to 36 months, depending on temperature, water salinity and food supply

Thin shellFeeding on tiny algae

develops a foot and eye spots cements itself to a “cultch-” (usually oyster shells)

metamorphoses into a tiny oyster

mostly male and grow rapidly

THE MATURATION TECHNIQUE IS WHERE THE CULTIVATION METHOD CHOICE IS MADE.

12 to 20 days

Sexual maturity can occur within 4 months in southern waters

“Seed” oyster

Reproductivity in Captivity• Oyster Farming Grows Market• http://youtu.be/MXyGad22cx8

• Broodstock is conditioned with high water flow, at low density, in well maintained growout equipment

• Algae is cultured for food• Hatcheries induce spawning by means of thermal shock • Spawning animals will be placed in separate containers

• Hatchery spawned tiny oysters are called “oyster seed”

• Because these have been spawn in a hatchery, they all are large (uniform size), and have the perfect shape,

• The spawn coould have been chosen for disease resistance and tripoidy• Which can be marketed to upscale restaurants for a larger profit.• ONE larvae cements itself on a SINGLE piece of microcultch.

• Growing off-bottom has many benefits• -single set oysters instead of clumps of oysters found in the wild • (Improve shell shape and appearance and Increase product consistency.)• -oysters suspended in the water column have an increased water flow• -availability of food (single cell algae called phytoplankton) throughout the

water column• -container provides protection from predators and eliminates burial in

sediment.• -Allow control of fouling (e.g., barnacles, overset oysters, mud worms);

Production Methods used (hatchery, nursery, growout)Seed is produced by hatcheries, young oysters ('spat' or 'seed') are moved to nurseries, then to growout sites, until oysters are mature and ready for market.

-Hatchery -In the hatchery phase, oyster brood stock is conditioned and spawned. The larvae are cared for until they become eyed and are ready to set

-Remote Setting- process in which larvae are set in a location away from the hatchery to make seed (reproduce). Adding this process allows the hatcheries to specialize in larval growth and the oyster farmer to specialize in oyster growth, improving production volume, and decreasing cost of production.Typically uses large tanks filled with oyster shells as cultch. This cultch can be sprayed onto large open-water leases and the oysters grown out on the bottom

-Nursery operations -In the nursery phase, small spat are protected from predators while growing them at high density to a size at which they can be transferred to sea-based growout. Key features of outdoor nurseries are that they operate on the flow-through principle, utilizing natural phytoplankton productivity to provide the food supply-Upweller

Upwellers are a common nursery approach, because they help the young oysters to grow quickly, and they are relatively easy to maintain, making them efficient and cost-effective.

-Production (growout phase) -The final phase is grower, where oysters bags are placed in the area in which they will grow to market size.Bottom seeding- majority of aquaculture oysters come from this method Off-bottom seeding-increasing in numbers in America because of many benefits

Adjustable Long-LineBottom CagesFloating BagsFloating Cage System

-Harvest- currently regulated the same way as wild harvest using the volume of oysters contained in a sack. Oyster farmers will likely want to sell by the piece (e.g., 200 oysters per sack). Note that each sack will require a harvest tag with appropriate records kept of harvest (temperature, salinity, etc.), transport and sales.

Hatchery-In the hatchery phase, oyster brood stock is conditioned and spawned. The larvae are cared for until they become eyed

and are ready to set.Hatchery • Broodstock conditioning are much the same for all bivalves. It is usual for a hatchery to

maintain its own stocks for production purposes in local, sea-based growout . These stocks are kept in the best possible conditions of high water flow and at low density in well maintained growout equipment. They are often the offspring of previous hatchery-reared generations, selected for desirable characteristics such as growth rate, shell shape and colouration.

– Water flow rate through conditioning tanks should exceed 25 ml per minute per adult and Density should be no more than 5 kg live weight biomass of stock should be held in a tank of 120 to 150 l volume. (or no more than 3 g adults per liter of water)

– For example, a tank of 150 l volume stocked with 50 oysters or scallops of 75 to 100 g live weight requires a flow of 1.25 l per minute at 25 ml per minute per adult.

• The most intensive culture methods involve spawning oysters in a hatchery and growing free-swimming larvae in large tanks supplied with specific algae (e.g., Isochrysis, Chaetoceros, or Tetraselmis) that are known to be nutritious for Larvae.

• Much of the effort and space in an oyster hatchery is devoted to producing the algae. Algal culture is very expensive in equipment and labor, and oysters eat a lot of algae, so hatcheries try hard to get their oysters out of the hatchery and into the natural environment as quickly as possible. (Photo 1)

• provide conditions of high food availability for 4-6 weeks in winter, just before thermal shock• The oysters are placed in tanks of shallow cold water at about 10 *C for four weeks. The

temperature is then raised two degrees per week to 24* C to mimic a springtime temperature increase, which induces spawning. (Photo 2)

• Spawning animals will be separated into Individual containers, so that eggs and sperm can be mixed in the correct ratio; to avoid over-fertilization, leading to deformed larvae. (Photo 3)

• Once larvae becomes eyed, is able to cement itself to a substrate.• As the larvae grow they are washed every few days through a series of graded sieves that

capture different size classes. The larger, faster-growing larvae may be separated from slower growing larvae

• ONE larvae cements itself on a SINGLE piece of microcultch. (Cultch-the hard substrate for which the pediveliger attaches to, in this case usually ground up oyster shells). Once attached, this larva will metamorphosis to become spat which will be marketed as “oyster seed” (Photo 4) . This technique produces a crop of single oysters which are desirable for the oysters-on-the-half-shell market.

• Example of oyster aquaculture improvement created by hatchery operations– Hatchery technology along with remote setting techniques have been instrumental in

freeing growers from unpredictable natural fluctuations in seed supply. – The division of labor has allowed commercial hatchery to focus on other areas of

interest, such as the improvement of oyster stocks through genetic manipulation.• Triploid Oysters• The development of the tetraploid technology revolutionized the oyster industry,

and many oyster hatcheries now offer triploid oysters.• Diploid oysters (left) and triploid oysters (right) showing differences in

summertime marketability. (Photo 5)• Oyster aquaculture is similar to traditional agriculture in that seed is selected for

improved survival and performance. • Two forms of improvements have been used extensively in the oyster industry:

disease resistance and polyploidy. • Research has developed disease-resistant strains of oysters through the process of

selective breeding. Triploid offspring have become available through the fertilization of diploid oyster eggs with sperm from a tetraploid male.

– Triploid-Sterile-Do NOT energy into reproduction-Faster growth rates-Improved meat quality (sterility>no

spawning>remain firm&full)-Available in summer (when diploids are

spawning>watery meat)

Upwelling basics for Nursery• When you are trying to set spat on microculch (tiny pieces of oyster shell) to get single oysters a method known as

downwelling is used and is most frequently a closed system (recirculating water). Once the spat are set upwelling is used and it can be an open or closed system but the methods we will refer to are all open systems or flow through.

• Upwelling brings a constant supply of nutrient rich water past your animals. Water is brought into the tank from a pump (low pressure high flow) which fills the tank and the only way for the water to escape is to pass up through the buckets, taking the algae rich water passed the young oysters. All they need to do is open up and feed, which they do constantly as long as the food is in the water. This method produces hearty oysters in short order that continue to feed at a rapid pace when placed out on the farm.

Nursery (Upweller-designed to protect small spat from predators while growing them at high density to a size at

which they can be transferred to sea-based growout)The basic idea for an upweller is to build a container('silo') having a mesh bottom; theoyster seed On the mesh, and water is directed up through the container. This allowsEach oyster to have Access to a lot of food, and wastes are carried up and away. Upwellerscome in many shapes and sizes, but they should be placed in an are with good feed (algae)in the water,and they should be easily accessed for maintenance.

Developing an shellfish nursery• Upweller design strategies – 4 options• Onshore within a structure• Onshore exposed to weather • Floating with shore power • Floating without shore power

• 1)Onshore within a structure• building next to the water• Protected from the elements • Reduces biofouling • Utilities nearby • User friendly

• But....! • Limited availability • VERY expensive!!! • Hard to justify for seasonal use • Need to lift water

• 2)Onshore exposed to the elements• Land /dock space next to the water • Less expensive than a building • Somewhat protected • Utilities nearby • User friendly

• But....! • Limited availability • Moderately expensive• Mother Nature • Exposed to outside tampering • Need to lift water

•3)Floating with shore power•On the water, frequently associated w/• a marina FLUPSY - FLoating UPweller SYsyem •At a water source • Lower operating costs •Utilities nearby •User friendly

•But...! •Limited access • Mother Nature! •Exposed to outside interference •Water quality

•4)Floating without shore power•On the water, frequently at a mooring. •At a water source • Mobile •Not dependent on shoreside utilities •Minimal operating costs

•But… • Limited access •Unprotected from nature and man• Utilities not nearby •Not user friendly

Production-Growout Methods

Bottom seeding-Bottom planting is one method used by many oyster growers, mostly because of low cost, and higher efficiency.-Oysters generally should be at least 1.5" in size before planting to the seabed. -Stocking densities are usually between 8-15 oysters per square foot-Benefit of low visual impact.

Off-bottom seeding (4 methods)-Growing off-bottom has many benefits-single set oysters instead of clumps of oysters found in the wild (Improve shell shape and appearance and Increase product consistency.)-suspending oysters in the water column leads to increased water flow-availability of food (single cell algae called phytoplankton) throughout the water column-container provides protection from predators and eliminates burial in sediment.-Allow control of fouling (e.g., barnacles, overset oysters, mud worms);

• 1) Adjustable Long-Line Systems– Mesh backets are 28’’ long with a grow-out capacity of approx 75 oysters. Baskets can be strung parallel to the

line or cross-wise. To control fouling of the baskets and oysters, baskets are routinely (e.g. weekly) lifted out of the water for approx 24 hours by placing line on the top riser clip. Baskets are easily handled and have a life span of 5 years.

•

• 2) Bottom Cages– Bottom cages measure 48”x36”x16” and are held off the substrate by two heavy gauge vinyl coated wire mesh

legs spanning the cage’s width. Each cage has two 5’ deep levels of mesh with a frame affixed to the top edge (like a picture frame). The frame supports a flat piece of mesh which serves as the top level’s lid. Cages are tethered to a long-line and their position marked with a small marker buoy.

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3) Floating Bags• The 33’’x18’’ bags of plastic mesh have floats attached to either side. The bags are

attached to tandem long lines. Each run holds approx 200 bags with grow-out capacity of 150 oysters/bag. Bags flipped over in place solves fouling on the bag, but not on the oysters. Bags are flipped on top of each other to ensure both oysters and gear receive fouling control, but this adds an extra visit to the bag to accomplish a full round of drying. When in waters of 8’+,hurricane plan calls for sinking 1 long-line to the bottom thereby suspending the bags in the water column(subsurface) where they are supported by the other two long lines

4) Floating Cage System• System consists of outer housing and interior shelves made of heavy gauge vinyl

coated wire mesh. Cages may have 4-6 compartments into which Vexar mesh bags, containing oysters, are placed. A door on one side of the housing allows for easy access. At final growout density, each bag can hold 150 oysters. Cages are tethered on each end to an anchored long-line. The FCS is supported by two air-filled pontoons. Routinely, the cage is flipped over onto the pontoons to allow for control of fouling on both gear and oysters. Before hurricanes, the system can be sunk by flooding the pontoons and refloated after storm passes.

Importance of Off-Bottom Cage CultureAdvantages in using intensive culturing methods, specifically off-bottom cage culture, include improvements in growth, reductions in predator-related mortality, &ability to control bio-fouling. Cage culture permits intertidal placement of oysters, such that oyster culture can take place in areas where the natural bottom is unsuitable for traditional, on-bottom cultivation (i.e., mud bottom and intertidal zones). Also, oysters cultured in intertidal zones, where they have been uniquely adapted to survive, have been reported to have accelerated growth, improved survival, and greater marketability through improved shell and meat quality when compared to extensively grown oysters. Furthermore, considering off-bottom cage culture methods are known decrease predator-driven mortality, higher salinity areas (>15 ppt) would become more viable areas for oyster production . Overall, intensive cage grow-out methods could increase the amount of total area for oyster production and facilitate oyster production in higher salinity areas.

Feeds and Feeding• Food supply for the first stage, which can be called the pre-conditioning stage, can be

in the form of algal pastes, bloomed natural phytoplankton• Filter feeders, oysters feed on plankton by opening their shells and pumping water

through their gills. This action traps particles of food.• Individual oysters are capable of filtering up to 50 gallons of water per day• Oysters remove particles from the water column, so they can consume and

concentrate human pathogens (e.g. bacteria and viruses that cause hepatitis-a, gastroenteritis, etc.) as well as toxins from blooms of certain microscopic algae ("red tides") that can produce paralytic shellfish poisoning in humans. Toxic hydrocarbons, pesticides, radioisotopes, and heavy metals may also be concentrated and sicken humans. Such public health issues can depress the market for oysters. North American governments have established programs to monitor shellfish growing areas for the presence of pathogens by use of indicator tests such as that for fecal coliform bacteria that may be associated with the presence of pathogens. In addition, the programs provide a sanitation guide for operating, inspecting, and certifying shellfish shippers, processors, and depuration facilities, and for controlling interstate shipments of shellfish.

Water Chemistry and environmental requirements in culture• Capable of tolerating wide temperature and salinity ranges from 0-42°C (32-107°F) and 0-42.5 ppt• Faster metabolic and growth rates are generally observed during periods of elevated water

temperatures. Salinity, however, and its synergistic effects with water temperature, ultimately determines oyster performance.

• Specifically, low salinity levels (< 3 ppt), when accompanied by high water temperatures, induce valve closure and decrease feeding rates

• Spawning of C. virginica is controlled by water temperatures and varies from north to south; northern oysters spawn at temperatures between 60 and 68°F (15.5 and 20°C), whereas southern oysters spawn at temperatures above 68°F (20°C).

• Oysters do best where salinities range from 10 to 30 ppt; the salinity range of 15 to 18 ppt is considered optimal.

• Oyster growth rates appear to thrive when the pH levels are between 6.75 to 8.75 pH with growthrates rapidly declining at either side of this range

• Oysters do best in areas where the bottom is relatively firm and stable, water flow is adequate to bring food, sediment does not smother oysters, and oxygen concentrations remain greater than 3 ppm (greater than 5 ppm most of the time)

Advantages and disadvantages of the species

• Disadvantages

• C. viginicus are much more susceptible to Perkinsus marinus (Dermo) or Haplosporidium nelsoni(MSX) infections than other species

• Predation and disease, which are mainly influenced by water temperature and salinity, are the primary contributors to natural mortality in the northern Gulf of Mexico, specifically in terms of excessive mortality due to protozoan parasite Perkinsus marinus (dermo) infections (Craig et al. 1989; Soniat 1996) and predation from southern oyster drills (Stramonita haemastoma) and black drum (Pogonias cromis) at salinities above 15 ppt (Breithaupt and Dugas 1979; George et8al. 2008). The yearly mortality rate due to P. marinus (dermo) has been estimated to be greater than 50% for market-sized oysters (La Peyre et al. 2003; Mackin 1962; Hofstetter 1977; Powell et. al 1996). While high annual mortality is generally offset by the almost continuous recruitment and rapid growth in the Gulf of Mexico, the economic impact of dermo and predation on the oyster industry has been substantial.

• Advantages

• C. virginicus Oysters are tolerant of a wide range of salinities and temperatures, and can tolerate a lot of handling; they are more 'forgiving' than many other shellfish species

• It is because of the resiliency of the species that the eastern oyster has provided a renewable resource for industry and commercial harvest worldwide.

• C. virginica dominates total oyster production in the U.S, accounting for ~68% of the total national oyster harvest.