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.
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.
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.
Red Drum are easily identified by their false eyespot located on the tail. Often, the tail and false eyespot break the water surface when red drum feed in shallow water. Shrimp and crabs are favorite food items of hungry red drum. Photo courtesy of NOAA. http://www.photolib.noaa.gov
Cool mornings this week reminded everyone fall is just around the corner. This subtle change in temperature inspires many of us to behave differently. It’s actually enjoyable to be outside again. Now, it’s easier to relax and drink a morning cup of pumpkin spice coffee on the porch or maybe take a brisk evening walk. These slightly cooler days not only announce the end of the dog days of summer but cue the natural world.
One of the most fascinating stories in nature unfolds this time of year. Red Drum or Redfish (Sciaenopsocellatus) are some of the most well-known and easily identified predators of the bay flats and marshes – But did you know these prized game fish can tell time? They don’t have calendars or watches but sense changes in water temperature and to the length of daylight : night time hours. Our calendar says September while their calendar says time to feed, migrate, and reproduce.
In the fish world, reproduction is known as spawning. It takes about three to four growing seasons for a red drum to mature and spawn. A mature four-year-old fish is about 28-inches in total length from head to tip of the tail. This size fish is critical to the continuation of the red drum population. This is one of the main reasons why fisheries managers regulate the number of 27 or 28-inch red drum caught. Limiting the number of this size redfish supports sustainable recruitment so there will be fish for years to come. Learn more about red drum fishing regulations by visiting Florida Fish and Wildlife at http://myfwc.com/fishing/saltwater/recreational/red-drum
When mature, red drum leave the nursery grounds of back bays and bayous and move to inlets and passes. This time of year, groups of spawning red drum may occur in entrances of the bay.
Notable members of Sciaenid or drum fish family include red drum, black drum, Atlantic croaker, and seatrout. Males have muscle fibers they vibrate against their swim bladder. The swim bladder is a hollow air filled sac fish use for buoyancy or depth control. When the muscle “strikes” the hollow sac a drum or drumming noise is created. The larger the fish the greater potential for noise. Male red drum often drum while spawning which generally occurs from sunset to sunrise.
In red drum hatcheries, light and temperature mimic the outside world and control spawning to support stock enhancement programs. In the hatchery, the drumming noise is loud and sounds like a bass drum being struck in rapid succession for about 10 seconds and then repeated. In the natural environment, Sciaenid drumming is so distinctive that researchers use hydrophones to locate and study fish species like seatrout and red drum.
While some fish species take care of their young and produce a few nurtured offspring, red drum overwhelm the odds of survival through shear numbers. During the two month spawning season, red drum spawning aggregations can produce millions of eggs each night. According to Louisiana Sea Grant, one female red drum can produce 1.5 million eggs in one night or 20-40 million per female each spawning season!
Spawning also occurs at the height of tropical storm season. Red drum eggs float on a tiny droplet of biologically produced oil that can be carried long distances by wind, waves, and water. In successful recruitment years, eggs and hatching red drum larvae make a journey into the most protected and productive portions of the bay or estuary in less than a week. Seagrass and submerged shoreline grass provide cover and protection. After rain and storms, adjacent land provides nutrients that naturally fertilize the bay waters. In response, algae and zooplankton bloom just in time to create the perfect first fish food for hatching red drum. The timing of red drum reproduction and survival is precise and elegant!
Juvenile red drum spend their next three to four-years growing to spawning adults, before migrating and starting the reproduction cycle over again.
Quick Facts: According to Texas Parks and Wildlife the oldest red drum ever recorded is 37 years old. The state record in Florida for red drum landed is just over 52 pounds and was caught near Cocoa in Brevard County, FL. A red drum caught in 1984 off the North Carolina coast holds the world record for largest red drum ever caught, 94 pounds!
An Equal Opportunity Institution. UF/IFAS Extension, University of Florida, Institute of Food and Agricultural Sciences, Nick T. Place, dean for UF/IFAS Extension. Single copies of UF/IFAS Extension publications (excluding 4-H and youth publications) are available free to Florida residents from county UF/IFAS Extension offices.
