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Seafood: Sex and the sinlge oyster
By Jackie R. Broach
A test group of oysters growing on Bill Chandler’s lease in Murrells Inlet — under the watchful eye of the S.C. Department of Natural Resources — seems to be growing about twice as fast as the oysters usually raised there.
“You can’t write a paper based on one sample, but we pulled a sample out and they were growing remarkably fast. It had nearly doubled in size since they put it in there three months ago,” Chandler said.
If the others in the test group on Chandler’s lease, and on six other coastal parcels from the inlet to the Coosaw River, prove to have a similar growth rate, it could mean an easier way for growers to produce single oysters.
With a higher value than cluster oysters, single oysters are a desirable crop. But they can be difficult to grow because of high levels of oyster larvae, known as spat, that exist naturally in the water, said Peter Kingsley-Smith, associate marine scientist and shellfish resource section manager for the Department of Natural Resources.
Oyster spat attach to objects in the water, such as wooden stakes, rope or shells. Once they attach, they remain there through their development.
“If you put out a piece of PVC pipe or some other material in the summer, it very quickly becomes covered in oyster spat,” Kingsley-Smith said. “With healthy, abundant populations of wild oysters, there are very high levels of natural recruitment [reproduction]. Growers put out a single oyster and that higher valued product gets settled quickly upon by wild oysters and they turn into clusters.”
Through a two-year research project funded by the S.C. Sea Grant Consortium, the department is trying to determine if a faster-growing oyster might solve the problem. Those oysters could possibly be grown later in the year, after most of the natural recruitment has finished, and be ready to go to market by spring.
The project seeks to compare the rates of survival and growth in different lines of native oysters, including triploids, which have three sets of chromosomes instead of the two normally found and are largely sterile.
“They’ve been used extensively in aquaculture for a couple of reasons,” Kingsley-Smith said. “First, sterility is advantageous if you’re using non-native species. If they escape, it’s less of a concern. The other aspect related to sterility is they have more energy to direct into growth.”
The project is the first to do a side by side comparison of triploids and diploids (oysters with the usual two sets of chromosomes) in South Carolina waters. The opportunity for such studies is limited because technology used to produce triploids is patented. The department is working closely on the project with the holder of the proprietary rights.
The project uses two diploid lines and one triploid line at the test sites. All were produced using a South Carolina female, but males from South Carolina and Virginia were used. In the diploid lines, this will help determine if there is any difference in growth or survival based on the genetic makeup of the fathers.
The females were transported to Virginia and the lines were started there in January, produced in mid-April and raised as larvae for several weeks at a lab. They were transported back to South Carolina on June 1 and carefully checked for disease, as are all shellfish coming into the state. Development continued in a nursery on Youngs Island and the oysters were placed at the seven test sites from July to September.
Monitoring of growth and development is ongoing.
“I think we’ll be able to tell at least for these three lines whether there is an advantage to using triploids,” Kingsley-Smith said. “We needed to do this as a first step. There are a lot of other steps that have to be taken if this technology is going to be pursued as the way to go.”
Chandler said it seems promising to him, so far.
“I can’t tell any difference in the taste of these and the others,” he said of the triploids. But he couldn’t resist joking that the sterile oysters might not have the reputed sexual effects of other oysters.
“Right now what I see is that they grow remarkably fast,” Chandler said. “We’re going to watch ‘em and see, and have a little oyster roast in March, toward the end of the season, if they grow the way I think they’re going to.”