Location: National Cold Water Marine Aquaculture Center
Project Number: 8030-31000-005-015-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2020
End Date: Aug 31, 2023
Objective:
The Aquaculture Genetics and Breeding Technology Center (ABC) at the Virginia Institute of Marine Science (VIMS), is the largest Eastern oyster breeding program in the U.S. and the only one to employ a family-based approach to select for growth and survival traits. Dermo disease significantly limits aquaculture production and there is ample evidence from field performance trials that the survival response to Dermo is heritable. Yet, the unpredictability of pathogen exposure attenuates selection for disease resistance in the field. The USDA ARS Shellfish Genetics lab has developed controlled laboratory challenge protocols to specifically define and measure Dermo resistance phenotypes for the eastern oyster. In several aquaculture species (e.g. Atlantic salmon, rainbow trout), the inclusion of challenge results in the selection process has augmented genetic improvement for disease resistance.
a. The primary objective of this cooperative agreement is to test the utility of integrating Dermo challenge results obtained by USDA ARS with the family-based breeding program at ABC-VIMS to generate disease resistant germplasm for industry. USDA ARS lacks the infrastructure and staff required to run a breeding program while ABC-VIMS lacks time and resources to conduct large scale challenge experiments. It is mutually beneficial for the two entities to pool complementary resources and expertise to address industry-wide Dermo disease management issues.
i. ABC-VIMS will provide biological materials and essential hatchery and field infrastructure to support ARS-based investigations of disease resistance and other related traits.
ii. USDA ARS will perform large-scale Dermo challenge experiments using said materials and share experimental results with ABC-VIMS.
The two parties will work together to evaluate the utility of challenge data in selecting for disease resistance.
Approach:
Brood stock oysters for family spawns are conditioned in late winter to assure early spring spawning. For spawning, individual oysters are shucked and a biopsy of the gonad is taken to determine sex and suitability of gametes. Males and females are stripped spawn, gametes cleaned, and stored in separate beakers before fertilization.
Spawning design is developed every year in accordance with results of progeny tests from the field and inbreeding calculations. Eggs for each female are divided evenly prior to fertilization with sperm from a different male, creating two half-sib families. From 80 – 100 families are produced yearly in this way. Fertilized eggs are reared in 60L, aerated, larval culture tanks filled with filtered sea water at ~26°C. Larvae are fed daily a ration of microalgae, starting with Pavlova sp. at 20,000 cells/ml, gradually including Chaetocerous neogracile and then Tetraselmis sp.
When larvae reach the pediveliger stage, they are removed from the larval culture tanks and set in a downwelling system on oyster shell ground to 400mm in size. When the spat are large enough to be retained on a 500mm screen, they are transferred to a land-based upwelling system where they are fed on raw water from the York River. At 10mm, spat are transferred to culture bags and raised through the fall and winter as bulk deployments.
Field Testing: Seed from families is deployed in replicates for progeny testing during the early spring (March-April) following the year of spawn and are generally 15-30mm in length. Individual oysters from each family are hand-counted and placed in labeled bags for survival and growth replicates. Husbandry on each field site includes regular maintenance to remove fouling, eliminate predators, and re-distribute oysters to promote uniform growth. Field testing of families lasts until the seed are 1.5 years of age. Measurements of survival and growth are recorded at 1.5 years after their spawning.
Replicated family groups are deployed at sites along a salinity gradient in Chesapeake Bay (Figure). Culture method is rack and bag at Lewisetta (L – Figure) and Australian long-line systems at Horn Point (H) and York River (Y).
Survival: At 1.5 of age, replicates for each family are assessed for survival. All oysters are removed from each unit and dead and moribund oysters are discarded. Live oysters remaining are counted and the ratio of live oysters to starting count are used to calculate cumulative survival.
Morphometrics: After survival analysis, a subset of oysters from each family replicate are randomly chosen for assessment of individual weight, shell shape and meat weight. Width index (WI) are calculated as the ratio of width to length. Height index (HI) are calculated as the ratio of height to length. Whole weight is recorded to the nearest tenth of a gram using a digital scale. Once external measurements are completed, oysters are opened and all tissue removed. Individual meats are allowed to drain of liquor briefly on a screen prior to recording meat weight. Meat yield (MY) is calculated as the ratio of wet meat weight to total weight.
