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Think Tank: Bigger, better oyster
Scientists put Pacific oyster hybridization to the test
March 05, 2011
Dennis Hedgecock is dreaming of bigger, better Pacific oysters, and the University of Southern California biology professor is determined to find out if it’s possible to produce them in the future. Recently, he and USC colleague Donal Manahan received a $394,000 NOAA Sea Grant that will allow the pair to determine which genes and metabolic processes are responsible for hybrid vigor in the oyster, and to develop a tag for identifying offspring with desired traits within hours of their birth.
“I’m very interested in the genetic improvement of aquaculture species,” says Hedgecock. “We have to do this, because we can’t keep returning to nature to get breed stock, which is what a lot of aquaculture does globally.”
The West Coast oyster industry is worth $72 million a year, and based on his initial, small-scale experiments funded by the U.S. Department of Agriculture in the 1990s, Hedgecock believes that growing hybrid Pacific oysters could be transformational. In those experiments, the first generation hybrid oyster grew twice as fast as the industry standard. That means West Coast oyster farm yields could potentially double.
Hedgecock and his team noticed that when you create inbred lines in Pacific oysters, they suffer from inbreeding depression. “The parent stocks of inbred oysters are small and don’t have many eggs,” he explains. “Cross those inbred lines, however, and you create a hybrid oyster that performs far better.”
Until now, translating this research into industry gains has been difficult. One challenge has been the insufficient supply of inbred broodstock required for routine commercial spawns. Hedgecock’s answer is to use large, robust, first-generation hybrids as the commercial broodstock. When two hybrid oysters are crossed, the result is a double hybrid, which should also perform better than wild oysters.
“We hope to show that the double hybrid is better,” says Hedgecock. “But we also just want to get the industry used to working with us, and to get information from the farms about the economics of oyster production in commercial farms. Without detailed data on production, it will be very difficult to say whether the double hybrids are an improvement.”
The research team has sent 100,000 double-hybrid seed oysters to three California farms: Hog Island Oyster Co. in Tomales Bay, Grassy Bar Oyster Co. in Morro Bay and Carlsbad Aquafarm in Carlsbad. The double-hybrid seed will grow alongside the same quantity of traditional seed.
By working with these oyster growers, Hedgecock’s team will be better able to assess double hybrid oyster growth — with results perhaps as soon as the end of the next growing season.
“My hope is that we’ll be happy with the double hybrids and that they will grow better than the controls,” he says. “Ideally, we’ll get some high quality information on how much it costs to grow this type of oyster, so in the future we will know if it’s worth breeding them.”
The on-farm trial, however, is the smallest part of the project. The largest component is directed at finding biomarkers or metabolic tags that will indicate when there are good hybrid combinations. “Creating the hybrid parent lines is a four-year process,” Hedgecock says. “We have to make inbred lines and then cross them to see what their combinations are. It’s very empirical and we can’t predict the outcome. This grant is about using biotechnology to say ‘this is a good cross,’ within hours of the birth of living larvae.”
In an effort to find those biomarkers, Manahan has been m easuring the
physiology of inbred and hybrid oyster larvae, noting their dramatically different growth rates within six days of birth. “One thing that’s shown up consistently is a difference in their efficiency for accumulating protein from the food they eat,” says Hedgecock.
“The inbred retains only 30 percent of the protein it consumes, while the hybrid retains 70 to 80 percent. So we’re now examining protein metabolism as a place to distinguish between various hybrids. How efficient are they at converting food into body mass? We’ll be looking for a correlation between gene expression and metabolism, as a source of predictive power about hybrids’ growth performance.”
Should the anticipated results of this research materialize and the researchers find the biomarkers they’re looking for, the West Coast shellfish industry might use exclusively hybrid seed in the future. “Were that to be achieved, this significant segment of U.S. aquaculture would have started up a path toward sustainable production of high-yielding, domesticated oysters, farmed efficiently in [coastal] waters,” Hedgecock says.
Contributing Editor Lauren Kramer lives in British Columbia