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Triploid eastern oysters are an important component of the Maryland aquaculture industry because of their fast growth and sustained high meat yield. Commercially, triploids are produced by mating tetraploid oysters with normal diploid oysters. Developing tetraploid stock is crucial to meeting the growing demand for Maryland triploid oysters. However, it is challenging to produce and maintain excellent tetraploid lines for the benefit of industry. In short, there is a clear and pressing need for triploid and tetraploid lines that have region-specific beneficial characteristics, especially tolerance to low-salinity environments. In this project, we will establish the first generation of tetraploid stock derived from Maryland local oyster populations. Several intermediate triploid and diploid lines used to produce the tetraploid will be developed through mass selection and deployed at three sites for performance evaluation in different geographic areas. This tetraploid stock will enable the production of new triploid seed with improved low-salinity tolerance and rapid growth, providing a foundation that can be used for the development of additional superior lines. The tetraploid line will be produced and distributed in collaboration with the Maryland Department of Natural Resources Piney Point Aquaculture Center. This collaboration will provide new triploid seed to Maryland growers. All lines will be maintained by MSU PEARL and new lines will be developed based on these stocks to provide continued industry support. Through the development of new triploid and tetraploid lines, this project will enhance the sustainability, profitability and resilience of the Maryland aquaculture industry.
Pass the (Low) Salt: Maryland Sea Grant (MSDG)Works With Morgan State University to Produce Brood Stock in Lower Salinities.
Partners: Orchard Point Oyster Co.; Madhouse Oysters; Johnny Oyster Seed Co.
Recap: Maryland Sea Grant helped support an oyster geneticist to develop brood stock oysters that thrive in low-salinity waters and will help advance oyster aquaculture and restoration in Maryland.
Relevance: Triploid oysters, also known as seedless oysters, put all of their energy into growth and none into reproduction, and have become the industry standard for aquaculture because they can grow all year and far more quickly than wild diploid oysters. Triploid oysters have three chromosomes instead of two, and geneticists create them by crossing a wild two-chromosome oyster (diploid) with tetraploid, which has four chromosomes, to make a three-chromosome sterile oyster. Geneticists also create triploids that are resistant to oyster diseases prevalent in the Chesapeake Bay. Many of Maryland’s tributaries, and portions of its Bay, have low salinities, so oyster farmers are interested in a triploid oyster genetically bred for low salinity water. Low salinity adapted oysters are also needed to help restore the region’s wild oyster population stock.
Response: Because salinities at the Morgan State University’s Patuxent Environmental and Aquatic Research Laboratory (PEARL) in Calvert County, are low, oysters successfully bred there are likely good candidates for aquaculture production in other low salinity waters in Maryland. During the COVID pandemic, Dr. Ming Liu, an oyster geneticist, worked with PEARL hatchery manager and MDSGExtension Program’s Brittany Wolfe-Bryant and two undergraduates to create tetraploid oysters from wild stocks in the Chesapeake. To develop tetraploids, the first step is to create triploids from diploid oysters through chemical (6-DMAP) -inducing method. Liu and his team investigated several techniques that could impact successful triploid production, including the method of spawning, chemical concentration, timing of chemical adding and treatment duration. This led them to develop a protocol with maximum triploid inducing rates for future spawns. This work also ramped up algae production at PEARL and gave students and staff in the lab more experience working with higher volumes of oysters.
Results: Liu and his team produced about 150,000 spat consisting of three triploid lines and two diploid lines. These new triploid oysters are adapted to Chesapeake Bay low salinity water and some were placed at Maryland oyster farms (Orchard Point Oyster Co., Madhouse Oysters, and Johnny Oyster Seed Co.) to evaluate their performance under different environmental conditions. The new, non-sterile diploid lines could be used for oyster restoration and/or on-bottom aquaculture in Maryland’s low salinity waters. These five new lines, developed in 2020, join a low-salinity diploid line produced in 2019and together will serve as key materials to create tetraploid stock in 2022. By 2023 it is anticipated that the oyster seeds created from these lines will be used to expand Maryland’s oyster aquaculture and public wild fishery in low salinity waters.