Oyster Farming is an economical and beneficial way of not overfishing the natural supply. Oyster farming in the United States has grown massively over the past few decades. As a result, it has a promising future in food sustainably. But how do you farm Oysters?
Oysters are farmed using the bottom or off-bottom culturing methods. The bottom culture is when the oysters are placed on the ocean floor to grow naturally. Off-bottom culture keeps the oysters off the ocean floor using various cultures such as cage, bag and rack, floating, and the suspended method.
Read on to discover the oyster's journey from tiny larvae to adulthood and some interesting facts about these tasty mollusks.
How To Farm Oysters?
Farming oysters can be a very satisfying way of making money. These fantastic tiny mollusks clean up the environment while they grow, adding to the fulfillment of the Farmer. The first choice to be made is where the oyster is coming from. Will the oyster seeds come from a reputable hatchery, or will it be done at the farm?
This can be a difficult choice as the financial impact is strenuous at the beginning of any business, and minimizing costs is essential. Either way, as a Grower, knowing how an oyster starts its journey is vital.
The hatchery is where it all begins. Seven stages must be accomplished in the hatchery to successfully hatch oysters.
Stage 1: Selecting The Best Site For The Hatchery
The location is vitally important in setting up a hatchery for the oysters. The site must have good water quality with a constant salinity range needed for quality oysters. A stable salinity range between 25-31ppt is vital in the hatchery. A lower salinity level will kill off the algae; thus, the salinity levels should not fluctuate. The water temperature should range between 68°F and 90°F.
Stage 2: The Algae Culture
Algae must be grown or readily available for the remainder of the oyster hatchery cycle. This is because algae feed the oyster larvae. The common cultured algae to use are:
- Isochrysis Galbana – a naked Flagellate that has a cell wall with Seta scales.
- Chaetoceros Muelleri is a Diatom rich in lipids or fats needed for the larvae during metamorphoses.
Algae are best grown in clear containers, cylinders, or large tanks to monitor the color and pH levels. When the algae become darker green, this is a good sign that the algae is growing and is healthy. The pH level for the seawater should be kept at a constant pH of 8 during the growing period.
The fast-growing algae will require lots of carbon dioxide for growth and photosynthesis. Therefore, the algae culture should be kept in a sunlit area but not in direct sunlight, as this will kill the algae.
Stage 3: The Broodstock
It is now time to prepare the Broodstock for production. The male and female oysters are fed the rich algae to prepare them for spawning during this stage. The oyster should be kept in 50°F (10°C) water for a period of four weeks. Every week, the temperature should be raised by 35°F - 37°F (2-3°C), mimicking the seasonal change.
When the water is at 75°F (24°C), the oyster will take roughly four weeks to change from an unripe (dormant) state to a spawning (ripe) state. When the oyster is ready to spawn, they will release eggs and sperm, spawning the next generation of oysters.
State 4: Spawning
During spawning, the male oysters will release their sperm into the water, stimulating the females to release their eggs. A female oyster can release 1 to ten million eggs during spawning. When the water in the tanks becomes cloudy, this is a sign that the spawning process has begun. Therefore, it is essential that the male and female oysters stay near one another, ensuring fertilization.
Stage 5: Larval Rearing
The embryo's development occurs immediately after the egg is fertilized, initiating the larval stage. After 48 hours, the free-swimming (trochophore) larvae will swim with the aid of tiny hair-like tentacles (cilia).
The larvae are filter feeders and feed on phytoplankton. It is essential to ensure that the salinity of the water temperature stays constant at 75°F (24°C) during this period, as the larvae will die if there are any drastic changes.
The larvae will enter a state of metamorphosis within 2 to 3 days to become Veliger larvae. A noticeable feature of the Veliger larva is its feeding organ or velum. After 14 days, the Veliger larva will have grown a foot. The foot will aid the larva to attach or cultch to a suitable substrate.
Stage 6: Setting The Larva
During the setting stage, the larva will use its foot to attach itself to a substrate. The ideal substrates (cultch) to use are dolomite, oyster shells, and other shell fragments. The containers used for setting should be stored in a low-light environment, as the larva will swim away from sunlight.
Once the larva has established a suitable site, it will attach itself to the cultch and enter another state of metamorphosis. The larvae will lose their foot and velum during this stage, becoming a spat.
Spats start off tiny and can only be felt as sandy grains on the cultch. During this time, the spat will start developing its shell. The spat will grow rapidly and is visible to the naked eye within ten to 14 days.
Once the spats are visible, they can be filtered through a 225-micron screen to produce single larval oysters. The spats are then collected and placed in moist paper towels, ready to be transported to a nursery or oyster farm.
Stage 7: The Nursery
At the nursery, the spats are placed in an upwelling tank and will be fed with unaltered seawater. The spat will feed and grow their shells for two to four weeks. At this time, the spats will resemble small oysters roughly 6mm (1/4") in size.
The small oysters can now be placed in small hexcyl baskets. The baskets can be placed in the oyster farm to let the small oyster grow for three months or until they are roughly one inch in size. The one-inch oysters are now ready to be placed in the chosen grow-out method.
The Different Grow-Out Methods
There are two common types of grow-out methods that are used. These are bottom and off-bottom cultures. The bottom culture is precisely what it says. The juvenile oysters are placed on the seafloor and left to grow. Off-bottom is when the young oysters are placed in bags or crates and put in the ocean without touching the bottom ocean floor.
The two methods are vastly different, but each has its benefits. On many oyster farms, the farmers will use both methods to achieve the required look or size.
Bottom Culturing Oysters
Bottom culturing is similar to growing wild oysters. The oysters will spread out and grow the same as the wild oyster, as they feed on the same nutrients. These nutrients play a significant part in the shell color and strength of the oyster. Bottom cultured oysters have a robust shell due to the nutrients they receive from the mud.
The frequent tidal waters and weather cause the oyster to tumble naturally in the ocean currents, producing hardier and deeper shells. However, letting the oyster grow in a natural habitat will expose them to the dangers of Mother Nature, as many oysters can die from suffocation in the mud. In addition, these oysters will be vulnerable to predators and extreme cold conditions.
Off-Bottom Culturing Methods
There are a variety of off-bottom culturing methods that can be used. The main difference between these methods is the growing equipment. The equipment is based on the area and sea state of the farm.
The advantage of off-bottom culturing is that the oysters are protected via enclosures. The enclosures will protect the oyster from most predators and the weather. The disadvantage of this form of culture is that it costs substantially more due to the required equipment. In addition, off-bottom growing equipment is more likely to be contaminated, which will need to be cleaned regularly.
The Cage Culture
The oysters are housed in grow-out mesh bags that are secured in the cages. The cage prevents the bags from sinking or floating away. The cages must be placed on a sturdy or solid ocean floor, as the weight of the cage may cause it to sink. This method of culturing gives the oysters the protection needed for a good yield and the benefits of bottom growing.
The Bag And Rack Culture
In the bag-and-rack culture, oysters are placed into grow-out bags. The bags are tied to a steel rebar rack or frame. This method is vastly dependent on the tidal range of an area. The area would need low enough tides for growers to access the bags.
The Tray Culture
The tray culture is very similar to the bag and rack cultures, except the oyster are placed in open grow-out trays. The trays fulfill the same function as the grow-out bags but allow the oyster to tumble more with the tide. The tumbling produces a more robust shell.
The Floating Culture
With floating culture, Growers can choose between varieties of different equipment. But as the name suggests, the equipment will float on the water's surface. Typically, the oyster will be placed in grow bags and suspended in the water. This results in oysters spending a lot of time in the water and rarely getting dry.
Another advantage of floating culture is that the oysters receive lots of tumbling due to the time spent in the water. When the bags become contaminated, they are simply flipped over to expose the seaweed and other ocean organisms to the sunlight and air.
The Suspended Culture
The suspended culture uses buoys that float on the water surface, and the grow bags are vertically suspended from the buoys. The suspended culture lets the grow-bags rise and fall as the tide comes in and out. The tidal movement constantly flips and moves the grow bags resulting in a hardier oyster with a strong shell.
Caring For The Oysters
Once the grow-out culture has been chosen, the oysters will be left to grow to a marketable size. This may take between eighteen and twenty-four months. During this time, the oysters must be taken care of to increase the yield.
As the oyster grows in size, the Grower must thin out the oyster in the grow bags. The oysters must be moved into more prominent and less cramped bags. This will allow the oysters to get more nutrients and grow larger much faster. The thinning-out process should be done every three to four months to prevent the bags from becoming overcrowded.
When the oysters are moved, they should be inspected and cleaned if any ocean organisms grow on their shells. Placing the similar size oyster in the same bags will aid in the final grading process.
When the oysters have reached market size, they should be taken closer to shore. This will be to have the shell exposed for half of the day. The exposed shells will harden, making the oysters ready for the consumer.
Diseases That Affect Oysters
Farming oysters may sound like an easy occupation, but diseases can happen unexpectedly, like in all types of farming. Below are diseases that oysters are prone to developing:
Perhinsus Marinus – is a prevalent pathogen found in oysters. This pathogen causes mass mortality in oyster populations. The disease is also known as Dermo or Perkinsosis and is not harmful to humans.
Haplosporidium nelsini- is a pathogen with a high mortality rate since the 1950s, and the disease is prevalent today. The disease is also known as MSX and was introduced during an experimental transfer of the immune Pacific oyster. MSX is not considered harmful to humans.
Marteilia – is a parasite of bivalves and causes QX disease in rock oysters. After the oyster is infected, it loses pigmentation in its visceral tissue.
Oyster Crab – are a white or translucent crab that lives inside the gills of an oyster. The Oyster crab feeds off of the food that the oyster collects.
Natural Predators Of Oysters
Oysters do not have many natural enemies, but if an infestation attacks an oyster farm, it can devastate the Grower's yield. The natural predators of oysters are:
Oyster Species That Are Farmed In The US
There are five common species of oyster that are farmed in the United States. They are:
The Pacific oyster is also known as the Japanese oyster or Miyagi Oyster. This oyster is native to the pacific coastal regions of Asia. The Pacific Oyster was introduced to Australia, New Zealand, North America, and Europe.
The shell of the Pacific oyster is large and rounded. It has radial folds that are shaped and rough to the touch, but this will depend on its environment. The two valves on the shell differ in size, and the shell is an off-white color.
Kumamoto (Washington) oyster or Kumies is grown in the Pacific Northwest and is native to Japan. This oyster has a delightful fruity taste and is often referred to as the Chardonnay of Oysters. Kumamoto oysters are small but have a robust and sturdy shell that is deeply cupped with distinct ridges. The shells can be dark brown with white and often have a green tinge.
European Flat Oyster
The European flat oyster is native to Europe and is farmed in Maine and Rhode Island. This oyster has a pear-shaped shell that ranges from 1.5 to 4.3 inches in length. It has a rough exterior with a light brown color, and the right valve has blue concentric bands on it. The valves differ, with the left being slightly concave and the right almost entirely flat.
The American or Eastern oyster is native to North and South America. These oysters provide a fundamental structural element to their surrounding ecosystem. They will settle on one another and form a coral reef. If a particulate enters its shell, the American oyster can produce a pearl. But it is small in size and has no monetary value.
The American oyster can usually grow between 3 to 5 inches but can reach lengths up to 8 inches. It has two rough shells that vary from white to light tan. The right side shell is flat, and the left is cupped with a distinctive purple blemish inside.
The Olympia oyster is native to the Northern Pacific coast of North America. The Olympia oysters grow between 2.4 to 3.1 inches and have a round or elongated shell. The shell is white to purple-black and may have yellow or brown stripes. The flesh of the Olympia oyster is white to olive green.
Interesting Facts About Oysters
Below are some interesting facts about oysters and oyster farming.
Oysters Can Change Their Sex
Oysters are born with sexual organs that give them the ability to produce sperm and eggs. They can only produce one at a time, but they can change their sex if the situation requires it.
Oysters Naturally Filter Seawater
Oysters have gills that are used to draw in water. The seawater is full of particles and plankton that become trapped in the mucus of the oyster's gills, thus filtering the water. One oyster can filter up to 190 liters (50 gallons) of seawater in a day.
The Flavor Of An Oyster Is Determined By Its Location
Oysters naturally filter seawater to extract nutrient-rich plankton and particles. This is the reason why oysters from different areas taste different. The type of particles and amount of plankton will determine its final flavor.
Oysters Have Clear Organs
Oysters have three hearts, and their blood and kidneys are colorless.
Oysters Are High In Vitamins
Oysters are a great vitamin enriched food. They are rich in Zinc, calcium, magnesium, vitamin A and B12.
Oysters Can Live Outside Of The Water
Oysters have a cavity in their shell that is filled with water. This allows them to survive for extended periods without opening their shells to feed. Oysters can survive for a long time out of the water in the cooler months, but freezing temperatures will kill them.
Harvesting Oyster Is Done By Hand
No machinery is used when harvesting oysters; it is all done by hand. This is because the oyster's shells are pretty delicate when they have been in the water for a few years.
Oyster Farms Help Save The Planet
Oysters absorb carbon, which is turned into calcium carbonate to strengthen their shells. They also help with climate change as they also absorb nitrogen. A three-acre oyster farm can clean the same amount of waste that is produced by 35 people.
Oyster Farming Is Very Profitable
A three-acre oyster farm will have roughly 250 thousand oysters, which will bring in about $200,000. The only catch is that the farm will need to wait up to three years to see any cash returns.
A farmed oyster's journey starts in the hatchery when the fertilized embryo becomes larvae. Within three weeks, it cultches onto a substrate. At this time, the larvae become a tiny oyster (spat) that can not be seen with the naked eye. In a further four weeks, the spat is a ¼ inch in size and can be placed in small hexcyl baskets to grow for three more months.
When the oyster is roughly one inch in size, it is placed in the ocean to grow. This can be done by bottom culturing, where the oyster grows naturally on the ocean floor. Or off-bottom culturing, when placed in grow bags and kept off the ocean floor. It will take a further 18 to 24 months before the oyster is large enough to go to market.
Five common types of oysters are farmed in the United States, Pacific, Kumamoto, American, European, and Olympia oysters.