A Brief Explanation About Triploid Oysters

A Brief Explanation About Triploid Oysters

When you sit down and enjoy some fresh, farmed oysters during the summer, you might notice that the oyster is not watery but yet plump and full of meat, unlike the usual wild oysters. These farmed oysters are very special and are called “triploid oysters.” What makes an oyster a triploid? Well, it all starts in the oyster hatchery and involves using tetraploid male oysters to breed with diploid female “wild” oysters.

Before we dive into triploids, let’s go over some definitions. A diploid organism contains two sets of chromosomes. As humans, we have two sets of chromosomes, and the pair is formed by a chromosome from the mother and a chromosome from the father. Triploid organisms contain three sets of chromosomes and while very rare, triploidy does happen in the wild. Tetraploid organisms have four sets of chromosomes and are usually only formed in a laboratory setting using pressure or other means to cause tetraploidy. When you breed a tetraploid oyster with a diploid oyster, the result is a triploid oyster.

Spawning Chamber
A hatchery worker keeping an eye on spawning chambers with diploid oysters – Thomas Derbes II

Inside of an oyster hatchery, you will see many small breeding chambers for the oysters. When a hatchery decides to spawn oysters, they place a single wild diploid oyster in each chamber. During spawning, the hatchery will introduce a cycle of cold then warm water and this cycle is repeated until a spawn is triggered. Hatchery workers will closely watch the oysters and will shut off the water supply to any oyster that has spawned so they can trap the gametes in the chamber. You can determine the sex of an oyster by watching it spawn; a female oyster “claps” out her eggs while a male opens slightly and releases sperm into the water. When spawning for triploid oysters, the hatchery workers will only obtain the eggs from female diploid oysters and discard any diploid sperm to avoid cross contamination. During the spawn, a worker will strip the sperm from male tetraploid oysters and once all female diploids are done spawning, they will introduce the tetraploid sperm to the diploid eggs. After 30 minutes, fertilization rates are calculated and stocking densities are formed.

Tub of Triploid Oyster Seed
3-month-old triploid seed – Thomas Derbes II

Why Would a Farmer Want to Grow a Triploid Oyster?

There are many benefits for a farmer to raise triploid oysters. First and foremost, triploid oysters are sterile. This is a major benefit for the farmers during the summer months. During the summer, wild diploid oysters spawn, and when they spawn, the meat turns very thin and watery. In the Panhandle of Florida, the harvest of wild oysters is prohibited in the summer and only farmed oysters can be harvested.

Another added benefit is the increased growth rate of a triploid oyster compared to a diploid oyster. As mentioned above, triploid oysters lack the ability to spawn. Since a triploid oyster does not have to spend energy producing gametes, it puts all of its energy into growing its shell and meat. A typical diploid oyster could take more than two years to reach harvest size, where a triploid oyster can reach harvest size within 8 months (commonly 12-24 months but there are usually some fast growers in a batch).

There are more benefits of triploid oysters including selective breeding for disease resistance and environmental sustainability. With the use of triploid oysters for oyster farming, wild stocks go relatively unaffected and help contribute to more sustainable aquaculture practices. I hope this brief explanation of triploid oysters will help you understand more about the somewhat unknown world of oyster aquaculture. With demand for oysters on the rise, triploid oysters hold great promise in meeting the needs of an ever-growing oyster aquaculture industry.

From Seed to Shuck – More Oyster 101

From Seed to Shuck – More Oyster 101

When you hear about oyster farming, you typically hear the word “seed” and how it is highly important to the future of the farm. While it might not be a typical seed that produces agricultural crops like corn, this seed is a living, breathing (albeit in the water) organism that produces a beautiful, cupped oyster. Depending on market size demand and requirements, it could take anywhere from 8 to 24 months to reach “shucking ready” size. Let’s take a dive into the timeline of an oyster, from seed to shuck.

Cooler Full of Seed Headed To Farm
A cooler full of R6 oyster seed headed out to the farm – Grayson Bay Oyster Company

Oyster farmers typically buy seed from an oyster nursery or hatchery, where they carefully spawn male and female oysters together in individual spawning chambers. Depending on the farmer’s needs, they can produce either diploid or triploid oyster larvae (more on triploids next week). These larvae are free-swimming for the first 2-3 weeks of their life until they develop into pediveligers (Oyster 101). Hatcheries will, for lack of better terms, mix the pediveligers with very tiny grains of ground-up oyster shells. These pediveligers will then attach to a single grain and begin to form into a “seed” oyster. Seed costs range and vary from year to year, and this cost is usually one of the biggest financial purchases oyster farmers can make. Seed is sold by size, starting at 6 millimeters (typically called size R6), and by increments of 1,000. Hatcheries and nurseries are located all along the Gulf Coast, but Florida law requires seed put in the Gulf of Mexico waters and estuaries must come from Gulf of Mexico hatcheries, and the same rules apply to Atlantic waters.

Oyster Seed
Oyster Seed (>R16) – Thomas Derbes II

Once purchased, these seed oysters make it to their homes in beautiful nutrient-rich waters and grow at a steady rate, and can reach an overall size of 2 inches in 4 to 9 months. During those months, the seed are filtering gallons of water per oyster per day, helping sequester carbon in their shells and consuming large amounts of plankton and algae that could contribute to the eutrophication of the bays. Oyster farmers will check on the seed almost weekly, changing bag mesh sizes and sorting the seed by size. Farmers will also take this opportunity to check for any oyster predators and swiftly evict them from their all-you-can-eat buffet. Sorting is done by using a “tumbler” that has a long drum with holes of varying sizes. This tumbler also helps clean the oyster and chip away at the lip of an oyster shell, causing the oyster to grow deeper and create a beautiful cup.

Farmed oysters do not have a size limit, but most farmers stick to a 2.5 to 3-inch size oyster. These oysters have filtered over 7,000 gallons of estuary water individually and sequestered a very generous amount of carbon, in the form of calcium carbonite (more here), in their shells in their first year of life. Once deemed ready for harvest, farmers will pull them out of the water and get them quickly in the fridge, following strict biosecurity guidelines and regulations to provide a safe product year-round.

Oysters of varying size
Some oysters are fast growers! These were apart of the same spawn. – Thomas Derbes II

And there you have it, from seed to shuck. With the holidays coming up, and seafood sometimes being a part of the holiday plans, reach out to the local oyster farmers in your area to reserve a dozen or two for your favorite uncle. You can also wow the crowd with this very fancy mignonette recipe below! 

Lemon Champagne Mignonette

Juice From 2 Local Meyer Lemons (They’re in Season!)

1 Shallot Chopped Finely

½ cup Champagne Vinegar

¼ cup Red Vinegar

1 tbsp each of Green and Pink Peppercorns 

24 Local Farm Raised Oysters (For the Environment!) 

1.       In a bowl, add the juice of Meyer lemons and shallots. Let it marinate for 10 minutes.

2.       Add champagne vinegar, red vinegar, and peppercorns to the lemons and shallots.

3.       Chill for at least 30 minutes in the fridge.

4.       Shuck oysters and top with freshly made mignonette. Enjoy!

Farmed Oysters Never Go Out Of Style

Farmed Oysters Never Go Out Of Style

Growing up in the South, I was exposed to many “Old Wives’ Tales,” ranging from not cleaning your house or clothes on New Year’s Day to the one that everyone, including the northern states, knows, “don’t consume oysters in months without an R.”  While most “tales” are full of superstition, the “R” tale was one of biosecurity, and was mainly truthful until two new types of “R” came about; Regulations and Refrigeration. The tale came about due to the rise in food poisonings from shellfish in the warmer summer months that do not contain a “R,” such as June and July. The rise in food poisoning came about from the practices used by the oyster “tongers” at the time. Commercial harvest of wild oysters is a very labor-intensive job that requires long days on the water and constant tonging, measuring, and sorting of oysters as they come off the bottom. During the summer, the oysters would sit on the deck of the boat for hours in the heat, causing microorganisms and bacteria to flourish inside the closed oyster.  Bacteria, like Vibrio, would replicate to harmful levels inside of the oysters and when consumed by a human, could cause life-threatening illnesses.

That was then, and this is now. While the consumption of wild Florida oysters during the summer is not allowed (closed harvest season for wild oysters during the summer in Florida), you can still find oysters from all over the US, and farmed oysters from Florida are still allowed to be consumed during the summer. Biosecurity is a major factor involving food production and aquaculture, and without biosecurity, the consumption of Florida-farmed oysters would be prohibited. Oyster farmers in Florida must follow a very rigorous biosecurity plan that includes State-issued harvest times, water-to-refrigeration requirements, reporting of harvest and planting, and twice-daily temperature monitoring requirements. The regulations for harvest times and refrigeration requirements have scientific backing, showing a statistical difference in Vibrio concentrations between properly handled oysters and neglected oysters, with properly handled oysters having little to no concentrations of Vibrio. For instance, during the summer months, oyster farmers must have oysters harvested and in the cooler before 11am and down to 45°F within 2 hours of storing in cooler.  

Boat Full of Harvest Oysters
A farmer returns early morning from the lease with harvest oysters covered by burlap. This keeps the oysters “cool.” (Photo by: Thomas Derbes)

While there is an increased concentration of harmful bacteria during these warmer months, properly cared-for oysters help limit the growth and proliferation of the bacteria. Another myth is that Vibrio doesn’t exist in cold, winter waters. Vibrio can exist year-round, and people with health risks, including immune-suppressed patients and those with diabetes, should exercise extreme caution when consuming raw seafood. When purchasing seafood for personal consumption, make sure to bring a cooler with ice and place your seafood above the ice, making sure to not allow any fresh water to touch the seafood. When storing seafood at home, make sure they are in a container that can breathe, and cover with a moist paper towel to keep their gills wet. Oysters are typically good for 10-14 days after the harvest date, so make sure you check the tags and consume within time.

Next summer, when you see farmed oysters on the menu, remember the new R’s and order a couple dozen for the table. The need for support from your local oyster farmer is most needed during those months without R, so slurp them down all summer and thank your local oystermen and women!

Oyster with French Mignonette Sauce
Locally Farmed Oyster with French Mignonette (Photo by: Kelly Derbes)

Easy French Mignonette Recipe

Recipe for 2doz Oysters

¼ cup Red Wine Vinegar

¼ cup Champagne Vinegar

1 tablespoon of Finely Chopped Shallot

1 teaspoon of Fresh Crushed Black Pepper

Juice of ½ Lemon

Combine all ingredients together. Spoon over shucked, chilled raw oysters.

Thanksgiving and the Sea…

Thanksgiving and the Sea…

I was trying to think of a topic that could connect Thanksgiving and our marine environment. Like many others, when I think of Thanksgiving images of Pilgrims and native Americans come to mind.  There is the turkey – and I wrote about “turkey fish” (another name for lionfish) last year.  So I continued to think.  One thing I do know about the native Americans who lived in this area, they liked oysters.  We find middens (piles of oyster shell) in many places around the Gulf coast.  These were discard piles from their consumption of the animal.  Lots of these indicate, at least to me, that they enjoyed them… and we do also.  Oysters are a part of Gulf coast culture and many have them with their Thanksgiving meal.

Oysters are one of the more popular shellfish along the panhandle. Photo: FreshFromFlorida

Oysters are one of the more popular shellfish along the panhandle.
Photo: FreshFromFlorida

Oysters are animals – meaning they lack cell walls and must consume their energy. The food of choice is plankton, sounds good doesn’t it!  They possess two tubes called siphons which basically filter seawater.  One brings water in, the other expels it.  As the water enters their body they filter it for food and oxygen.  As it leaves they expel waste and carbon dioxide.  At times sand is sucked in and becomes lodged – they cannot expel.  This “irritant” is covered by a material called nacre and becomes a pearl.  Most are not round nor pretty but occasionally there are nice ones…  Pacific oysters make better pearls.  Amazingly a single oyster can filter up to 20 gallons of water in a day during the warmer months.

 

They are invertebrates and belong to the phylum Mollusca – meaning they have a soft body. Many invertebrates have a soft body, but what makes mollusks different is that they have bilateral symmetry (a head and tail end), a coleomic cavity (which allows organ development and increased size), and unique to them is a tissue called a mantle (which can secrete a calcium carbonate shell – and most mollusks do this).

 

Oysters are in the class Bivalvia – meaning they have two shells connected by a hinge at a point called the umbo. Other bivalves include the clams, scallops, and mussels.  All of these are popular seafood products.  Oysters differ from other bivalves in that they are cemented to a structure and cannot move around (sessile).  Many mussels are sessile also but oysters differ in that they use calcium carbonate to literally cement themselves to the substrate, where mussels use a series of threads to do this.  Cementing to the substrate means that they are picky about their habitat – it needs to have a hard substrate, sand will not do.  We all know this.  Place a piling, clay pot, board, or boat in the water… and oysters find it.  Typically, they will attach to each other and form small clumps of oysters.  These clumps form larger structures we call oyster reefs (or oyster bars) and this is what the commercial oysterman is looking for – and the recreational boater is trying to avoid!

 

So how do these oysters, who are sessile, find these habitats? Well, when it is time to reproduce oysters (which are hermaphroditic) release their gametes into the water.  The sperm and egg that find each other form a planktonic larva called veliger.  To increase the chance of finding each other the oysters release their gametes at the same time – a mass spawn.  There are a variety of factors that trigger this but water temperature seems to be an important one.  The veliger drift in the currents, developing into juveniles, and then settling out as small oysters called spat.  If the currents have brought them to a good location, the spat settle on a hard substrate and the next generation begins.  If not, they die.  So literally millions of fertilized veliger are produced from individual adults.  In many cases the suitable substrate are other oysters.

An oysterman uses his 11 foot long tongs to collect oysters from the bottom of Apalachicola Bay Photo: Sea Grant

An oysterman uses his 11 foot long tongs to collect oysters from the bottom of Apalachicola Bay
Photo: Sea Grant

Today oysters seem to be in trouble. Large bars have disappeared due to dredging and over harvesting.  Hurricanes certainly do damage to some and poor water quality alters their growth and development.  Recently problems in Apalachicola include the lack of river water reaching the Gulf.  The higher salinities created by the reduction of river flow have increased the number of oyster predators (starfish and snails) as well as diseases.  All of that said, they are still a popular seafood item and enjoyed by many during the holidays.  The cooler months mean less bacteria in the water and fewer problems consuming them raw.  Cooked oysters have few problems… period.

 

I hope all have a Happy Thanksgiving and if you have not tried oyster dressing, maybe this year could be the year.

 

Happy Holidays.

Working to Restore Oyster Habitat

Working to Restore Oyster Habitat

Nature has provided us with an incredible resource in the diverse assemblage of molluscan shellfish that inhabit our coastal bays and estuaries. One bivalve species in particular provides many human benefits. The eastern oyster (Crassostrea virginica) has not only proven to be a preferred food species for people but also derives many vital ecosystem services through its existence in our near-shore estuaries.  Oysters are born as planktonic larvae that drift in the water for about 2 weeks.  They are called a spat when they settle out of the water column and glue themselves to a suitable hard surface, such as another oyster shell, and begin to grow their own shell.  Oysters feed on particulates in the water throughout their life and when mature can filter as much as 50 gallons per day.  Because of this life style they provide some degree of water purification and improvement in water clarity.  The structure of an oyster reef is also a valuable habitat component which provides shelter for a plethora of small creatures that support a vast food web in the estuary ecosystem.

 

Oystermen participate in shelling program for Apalachicola Bay

Oystermen participate in shelling program for Apalachicola Bay

Barges will also be used to relay shells for replenishing oyster habitat.

Barges will also be used to relay shells for replenishing oyster habitat.

 

 

 

 

 

 

 

 

Although we have several native species of oysters in the Gulf of Mexico the eastern oyster is the only species that supports a commercial industry.  in Florida, the bulk of that industry has traditionally been centered around Apalachicola Bay in the mid-Panhandle region of the state.  This one estuary system typically produces 90 percent of the state’s oyster crop and 10-13 percent of the nation’s harvest.  Some good harvest years have yielded 4-6 million pounds of oyster meat (shells excluded) from this single bay.  In recent years however there has been a dramatic decline in oyster abundance. The industry, along with concerned natural resource managers, is seeking to rebuild numbers to a sustainable harvest level.  The reasons for this precipitous drop in numbers is the subject of much debate but savvy natural resource professionals believe a combination of factors have been involved over several years to cause the current situation.

 

Fossil oyster shell being relayed to bay bottom.

Fossil oyster shell being relayed to bay bottom.

So, how do you bring back a thriving oyster industry from the brink of collapse?  Several factors need to be considered and addressed as part of a holistic management approach.  At the present time there are two primary mechanisms being employed to support increased oyster recruitment to Apalachicola Bay.  The first involves “planting” a suitable material on the bay bottom for oyster spat attachment and growth.  In the past this has primarily consisted of oyster shells from the shucking plants.  More recently the industry has been employing the use of fossil shell material from a local mine.  Oystermen are being employed to transfer the shell from land-based loading areas to the designated deposition sites in the bay.  Funding is also forthcoming to allow shelling by barges to cover more area.  The other strategy to assist with recovery has involved the use of regulatory authority in consultation with local experts and oystermen with decades of experience on the bay.  This approach can reduce the harvest pressure on oysters and support a more rapid recovery, given proper conditions in the estuary.  Bag limits have been reduced, enforcement has been stepped up to ensure compliance with the rules, and harvest areas have been adjusted.

 

Oystermen line up early to receive shell for relay project.

Oystermen line up early to receive shell for relay project.

There are, of course, other important aspects to the solution for bringing back the thriving industry of the past and many of them relate to natural cycles of drought and flooding.  Increasing human demands for water from the river system that feeds the bay tend to magnify the effects of natural drought cycles.  If salinity remains high for longer periods there is an increased pressure from oyster predators that typically are limited by lower salinity.  Factors related to oyster diseases and parasites are also in the mix.  To say that it is a complicated situation would be an understatement.  Researchers who have studied the system for their entire careers find it difficult to quantify the problems and solutions for this large, complex natural ecosystem that has been an important cultural and economic component of Florida’s makeup since early humans roasted or cracked open the first oyster.  Hopefully, with enough concerned partners working towards effective management strategies we can once again enjoy in abundance the wholesome, delicate morsels that have been called the food of the gods.

 

Article by: Erik Lovestrand

Franklin County Extension Director

Sea Grant Regional Agent II