Frequently Asked Questions
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to find answers to the most common TOGA and oyster gardening questions.
Human Health and Personal Safety
Where can I get spat and how much do they cost?
Is spring or fall better for buying spat?
Are the larger spat worth the additional cost?
Should I buy fertile (diploid) or sterile (triploid) animals?
For a list of spat/seed providers - Spat Center. 1000 spat will sell from $30 up, dpending on size and vendor.
Spat purchased in fall will have been produced earlier the same year and might escape infection by either MSX or Dermo during their first summer. Spat purchased in spring will likely have been over-wintered and will need to survive two summer’s potential exposure to disease before reaching market size. If you can get the hatchery-produced strains that have some disease resistance, it probably doesn’t matter.
Larger spat suffer less mortality, will reach market size sooner, and can be kept in coarser mesh, resulting in more circulation and less maintenance.
If you intend to eat oysters in summer, sterile animals are better because they do not “waste” energy making eggs/sperm, so they are “meatier.” Fertile animals are just as good to eat during winter months and provide an important ecological service by releasing eggs and sperm for re-colonization.
When do oysters spawn?
Can you tell a male from a female?
How are oyster spat produced?
How are triploid (sterile) oysters produced?
What is so special about a triploid?
Are triploids considered genetically modified organisms? (GMO’s)
How long does it take to get spat to edible size (~3 inches)?
Oysters can spawn at any time during the growing season, but most spawning takes place in July, plus or minus a week. See the Fall 2010 and Spring 2013 TOGA newsletters.
Not unless it is shucked open and a sample of the reproductive tissue is examined under a microscope. Eggs are fairly obvious - round and large, sperm are non-distinct wiggly particles
Quick answer – the lifecycle of the oyster is manipulated inside a land-based hatchery using highly filtered river water and providing high quality food (also grown in the hatchery).
Long(er) answer – Hatchery components:
Parent animals, selected for desirable traits like disease resistance and longevity, are “tricked” into ripening out of the normal season by the manipulation of temperature and food. Batches of broodstock are kept ripe from March until September - the hatchery “season”. Oysters in the wild have a much more limited season and spawn once, and in some cases, twice in the summer.
(2) Food Production (algae)
Large volumes of algae species are cultured to provide the best nutrition for growing oyster larvae
Typically done by shucking open the broodstock and scraping the egg and sperm into containers through a process known as “strip spawning”. Eggs and sperm are mixed in the right dose and fertilization takes place in a beaker or bucket
(4) Larval culture
The free-swimming oyster larvae grow for about two weeks in large tanks of highly filtered river water until they reach their terminal life stage. The development of an “eye spot” indicates the larvae are ready for settlement and metamorphosis. These “eyed larvae” are harvested and transitioned to either downwelling systems where they settle on microcultch (ground shell particles) and become single oysters or they are transported to remote setting facilities and provided with clean oyster shell to settle and become spat-on-shell.
Triploid oysters are produced by mating. Sperm from specially-bred male oysters, called tetraploids (4 set of chromosomes), are combined with eggs from fertile females and the progeny have three sets of chromosomes (triploids).
Triploids are sterile; they don’t expend energy to get ripe and spawn. That makes them faster-growing than fertile oysters. This also makes triploids edible year-round; with plump meats in the summer months when fertile oyster meat quality is poor because of spawning.
NO! Triploid oysters are mated (male oyster x female oyster). There are no chemicals or insertion of foreign DNA involved.
Using hatchery-derived strains, you should expect spat to begin to reach market size in 18 months. Research shows triploid oysters do grow faster than diploids in Virginia waters but much depends on husbandry and local environmental conditions. Diploid selected strains outcompete the wild oyster.
Where can I get floats/cages?
Which kind of floats/cages works best?
How can I get my heavy floats up on the dock?
How often should I clean my cages?
Several options are available:
(1) Build your own – attend TOGA’s oyster float building workshops (more info on TOGA’s website – EVENTS link)
(3) See Contact US.
Bottom cages can only be used on hard bottom, are heavy, and can result in slower growth than floats or cages suspended from a pier. Floats grow oysters efficiently, but must be tended and kept from banging into pilings or bulkhead. Many people find them unsightly. Various kinds of cages can be suspended from piers, but in order for them to be managed easily; they cannot hold as many oysters as bottom cages or large floats. Go to the TOGA Web site (www.oystergardener.org) and open “Resources (Equipment, info etc.)” at the lower right.
Some people use their boat lift whereas others devise or purchase small “cranes”.
When fouling organisms like algae, sea squirts etc. begins to restrict water circulation. Gear doesn’t need to be spotless but it needs to have adequate water flow for oysters to feed.
How can I repopulate the waters around my house with oysters?
Can an oyster gardener get shell and larvae for a spat-on-shell home project?
How can I donate my adult oysters if I don’t want to eat them?
What is the best way to dispose of oyster shell, which is becoming a limited resource?
Supply substrate, especially clean oyster shell, in July +/- one week. Larvae are free-swimming for about two weeks and it is very unlikely that the progeny of any fertile oysters will end up back where they were spawned. Don’t rely on natural strike, as there are good years and bad years – see articles in the Fall 2010 and Spring 2013 TOGA Newsletters.
It is not practical to “do-it-yourself” but one of the commercial aquaculture operations might sell them to you, or you can pay them to do a strike of at least about 30 bushels.
A bushel of shell costs about $3.00 and the larvae to strike on a bushel cost about $8 per million (must be bought by the million). A good ratio is 3 million larvae to every 100 bushels of shell.
The Chesapeake Bay Foundation conducts oyster restoration.
Don’t throw it in a landfill - find a shell-recycling center near you. TOGA is now collecting shells for a restoration project in the northern neck. Contact Us.
Can someone do a site survey or help me with a specific problem(s)?
Do oysters need to be fed?
Will oysters freeze in winter?
How fast do oysters grow?
Does run-off, fecal matter and E. coli hurt the oysters?
How can I determine my salinity?
How long can oysters stay out of the water?
How long will oysters keep in the refrigerator?
Where do oysters grow best?
What do I do with my oysters to prepare for a hurricane?
No. There are sufficient algae in the water to support their growth.
Large oysters are remarkably tolerant to the cold. Small seed oysters are not as tolerant and will likely have higher mortalities over the winter. Oysters can survive if they are under a layer of ice but they are very susceptible to sub-freezing air temperatures. You do not want your oysters exposed to wind chill. In preparation for winter: move oysters to deeper water (if possible); secure float lines; and do not sort or handle in frigid temperatures (this will induce mortality).
Growth rate is very variable. Spat should reach market size (about 3 inches) in 18 months given good circulation and salinity higher than about 8 parts per thousand.
Too much sediment can make feeding difficult but the pathogens like E. coli that affect humans do not affect oysters. (From a consumer health standpoint – you don’t want to eat oysters from your garden after a heavy rain)
You can purchase an inexpensive hydrometer at an aquarium shop because people use them to monitor salinity in salt water fish tanks. Salinity Refractometers can be purchased online for as little as $20. Check Salinity maps of the Bay. But remember, salinity can vary tremendously with heavy rainfall and it is not uncommon for the water at the surface to have a lower salinity than the water on the bottom after a heavy rain.
Small oysters will not survive more than a day or so in the shade whereas large oysters can survive for a week. You should not eat oysters that have been out of the water for more than 24 hours because any bacteria they harbor can grow exponentially.
They can survive in the fridge for about 2 weeks (and sometimes longer) BUT if eating raw, it’s best to properly refrigerate and consume within 1-3 days. To keep oysters from drying out, cover with damp paper towels. Any oysters gaping open should be discarded.
Ideal conditions are:
(1) Plenty of water flow and circulation or tidal flushing of waterway. This provides good oxygen, lots of food (plankton) and the removal of the oyster’s waste products
(2) Optimal salinity - greater than about 8 parts per thousand
If you cannot secure them against a storm surge (the hurricane of 1933 had a 8-foot surge) get them out of the water in a shaded place and keep them moist. Large oysters can survive for several days out of the water
Human Health and Personal Safety
If I get cut by an oyster how should I treat it?
How can I find out if my water is restricted for harvesting?
If my water is condemned, can I safely eat my oysters?
Is it safe to eat oysters raw?
Is it dangerous to eat oysters infected by MSX or Dermo?
Is it safe to eat oysters in summer, and why do many people only eat oysters in the “R”-months?
Any break in the skin while in the water should be thoroughly washed in warm soapy water immediately. Some people also apply an antiseptic. If you experience swelling, pain or any other symptom go to a hospital immediately and tell the physician that your wound was in contact with salt water.
Go to Shoreline Closures. This will take you to the VA Dept. of Health, Division of Shellfish Sanitation.
Eat at your own risk. First, get educated as to the particular condemnation classification of the area. (see answer above for how to do this) Thorough cooking is required to render the meat safe from bacteria.
Nobody with a compromised immune system should eat raw oysters. This includes people who take medication that lowers their immune response.
Oysters can be enjoyed safely by understanding risk factors and by using best harvest practices in the garden.
Best harvest and handling practices for gardeners: oysters for raw consumption should be refrigerated immediately after harvest and be kept under refrigeration until the moment they are consumed. Do not harvest oysters after a heavy rain – wait several days for them to purge any contaminants from runoff.
No. The two oyster diseases do not affect humans.
The idea of not eating oysters during months without an R comes from the fact that the bacteria that can affect human health is more prevalent in the summer months and fertile (diploid) oysters produce eggs and sperm in summer, making the tissue watery. With modern refrigeration, the use of sterile triploids, and safe handling practices, oysters can be enjoyed year round. However, nobody with a compromised immune system should eat raw oysters. This includes people who take medication that lowers their immune response.