Location: National Cold Water Marine Aquaculture Center
Project Number: 8030-31000-005-062-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jun 1, 2024
End Date: May 31, 2025
Objective:
Dermo disease is widespread along the East and Gulf coasts of the US and thus is a significant issue for the oyster aquaculture industry. The cooperator has been operating a multi-trait family-based breeding program for eastern oyster in the Chesapeake Bay for > 10 generations, but they do not directly select for Dermo resistance. Previous collaborations between USDA ARS and the cooperator focused on the development of a disease challenge model and its utility in genetic improvement for resistance. For three consecutive year classes, USDA applied their disease challenge protocol to pedigreed families from the cooperator’s breeding program. Genetic parameter estimates suggest that survival in response to challenge is heritable; but survival in response to laboratory challenge and on-farm survival for siblings of the lab challenged animals was not highly correlated. It is unclear what factors (other parasites, environmental stressors) affect survival at the farm site.
To understand the relationship between survival in Dermo laboratory challenges and survival to Dermo exposure in a field setting, especially as it relates to breeding disease-resistant stocks, it is necessary to conduct further experiments that assess parasite prevalence in field-exposed families and closely monitor them over time for survival and Dermo infection during the seasonal window for natural parasite exposure and disease proliferation. This research will also inform how best to advance Dermo disease resistance breeding activities (lab challenges vs. field deployments) in regional eastern oyster breeding programs.
Approach:
All spawning activity will take place at the Acuff Center for Aquaculture hatchery on VIMS campus. Field deployments of families will occur in the adjacent York River on the VIMS oyster lease. The spawning design will be developed using a combination of high survival and low survival families selected from performance of laboratory challenged families. A subset of 10 new H and 10 new L families will be created while keeping inbreeding coefficients to a minimum.
For spawning, individual oysters will be shucked and a biopsy of the gonad taken to determine sex and suitability of gametes. Oysters will be stripped spawned and families will be created using single pair matings. A mantle biopsy from each parent used in the spawns will be preserved for downstream genetic analyses. Oyster larvae will be reared in 60L culture tanks at ~26°C and fed a daily ration of live microalgae. Every other day, larvae will be assessed for health and tanks will be cleaned to maintain optimal water quality. When larvae reach the pediveliger stage, they will be transferred to a downwelling system and set on 400µm cultch. When the spat are large enough to be retained on a 500µm screen, they will be transferred to a land-based upwelling system and raised in raw water until they reach 10 mm shell length. At that time, spat will be transferred to duplicate culture bags and raised as bulk deployments (~1300 seed per bag) through the fall and winter. Husbandry during the fall will eliminate fouling organisms such as macroalgae and tunicates or predators such as juvenile blue crabs.
In early March 2025, 20 individuals per family will be sacrificed and preserved for an initial assessment of disease prevalence and mean seed size per family. Size will be assessed by measuring whole weight and shell length. Mantle tissue will be collected and preserved. Then 200 oysters per family will be counted into three replicate baskets per family and deployed on the farm for progeny testing. Survival will be monitored in May, July, and September, at which time the number of live oysters per basket will be counted. A subset of oysters per replicate will be removed, measured and shucked. A piece of mantle will be preserved for downstream parasite load assessment. A final assessment will be performed in November 2025.
DNA will be extracted from all preserved tissue samples using Kurabo QuickGene Tissue DNA kits (Autogen) following manufacturer’s protocols. Post extraction, DNA quantity/quality will be determined, and DNA extracts standardized to 50ng/ul for downstream qPCR analyses. Parasite quantitation will be performed according to USDA ARS standard operating procedures.
Survival and parasite load, as detected by qPCR, will be analyzed using quantitative genetic analyses via ASReml-R to assess genetic correlations between field survival and Dermo disease acquisition.
