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Eyed  Larva Oyster tanks. Oyster Planting spat_on_shell_plant.jpg check_cage.jpg cages.jpg harvested_clump.jpg measure_oyster.jpg

camera iconEyed Larva:  A photomicrograph of an eyed oyster larva.

Photo by Michael Congrove.

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We pursue a number of research projects that inform and thus enhance our breeding program. Many of these are accomplished through our family breeding program, whose purpose is to provide detailed estimates of genetic and environmental contributions to economically important and desirable traits.

Quantitative genetic studies of growth rate

In the absence of disease, fast growth rate is emerging as the primary breeding objective in Virginia, particularly in low-salinity areas where mortality from the diseases MSX and Dermo is low. Commercial operations aim to harvest their crop in 18 months. Can we improve this by selection? If this is the case how early in the grow-out cycle is it possible to select oysters for size? Early selection can reduce the handling of oysters in the field and perhaps shorten the generation time from 2 years to 1. Are there environmental conditions that will retard or realize this genetic potential? To answer these questions, we are using our family breeding program to estimate the heritability and genetic correlations between early and late growth. We are also growing our families under various environmental conditions (salinity, temperature, and depth) to understand and quantify non-genetic contributions.

Genetic correlations among old and new traits

For a number of generations, our principal selection trait has been resistance (tolerance) to the diseases MSX and Dermo. However, as oyster aquaculture develops, new traits of importance are coming to the fore. It is no longer sufficient for our animals just to survive until harvest. We are now incorporating other production traits such as fast growth rate and high meat yield to add more value at harvest. This begs the questions, are these new traits positively or negatively correlated with disease tolerance, and each other? Furthermore, all our emphasis has been placed on grow-out performance but there is another side to oyster aquaculture, the hatchery. Starting in 2010 we will begin a series of long-term breeding trials to define hatchery traits and determine the possibility of improving these traits by selection and the consequences these could have on previously selected field traits.

Variation in disease resistance among natural populations

Certain natural populations have been shown to harbor resistance to the diseases MSX and Dermo. For example, Louisiana oyster populations are tolerant to Dermo disease. We are systematically examining local Chesapeake Bay populations from 4 different rivers, which are believed to have developed tolerance to these diseases. Survivors from a two-year natural disease challenge will be used to develop a new line—the WTS (Wild ThingS).

Examining variation among different sets of triploid progeny

Triploids are fast becoming the animal of choice throughout Virginia. This is because of their proven superior growth and high survival, even under intense disease pressure. Can we further improve their performance by breeding? This sounds like an oxymoron because these animals are sterile, but it isn't. This is because in addition to the standard tools of selective breeding, ABC also has technology to increase chromosome numbers of oysters, so-called polyploid production and we produce triploid (3n) oysters—containing an extra set of chromosomes—by using tetraploid (4n) and diploid (2n) parents. Triploids are made by mating 4n males with 2n females. We have begun testing to see if breeding better triploids is possible. The first step in this process is to see if and how much variation exists among triploid spawns produced from same tetraploid males and different females. This will tell us if the genetic advantage from a diploid female is carried into the triploid cross and thus if selection for an improved triploid is possible. We are also making several new pure-bred tetraploid lines for an upcoming crossbreeding experiment. Managing tetraploid broodstock populations represents an extensive program, which can be considered distinct from our family and line breeding programs. To what degree will tetraploids have to be managed to optimize their use, or are triploid produced from them more or less equivalent?

Stability of polyploidy oysters over time

We have been systematically examining triploid and tetraploid populations of oysters for chromosome stability. We know that both tend to lose chromosomes over time. For triploids, this process is slower than tetraploids. Does this chromosome loss affect sterility of triploids or fertility of tetraploids? Are there implications for evolutionary processes?

Research by ABC graduate students

Stephanie Reiner—New hatchery methods will increasingly play an important role in providing high-quality larvae and seed to the industry. One of the technologies receiving more and more attention is high-density larval culture. For C. virginica, there is insufficient research and development on the promise and limitations of this type of culture. ABC has set up an experimental facility in conjunction with a local commercial hatchery to further investigate the potential of high-density culture.

Brian Callam—The production of triploids for commercial culture is an increasingly important genetic enhancement, judging from the growing popularity of triploid seed. There are many questions associated with the optimum management of the tetraploid broodstock that are used for triploid production. What role does heterosis play relative to additive gains? Brian is beginning a project to determine heritability of various characters associated with tetraploid X diploid crosses.

Erin Schramski—Brood stock that produce high-quality gametes (i.e., high fecundity and good egg quality) is paramount to high-quality larval production and volume output. Thus, conditioning oysters for spawning is a key activity for research and commercial production. There are many factors that contribute to broodstock quality, but genetics has seldom been examined. Erin seeks to determine how selection influences disease resistance (as run by ABC) on reproduction of C. virginia by comparing relative performance among families.