Wild stocks of eastern oyster Crassostrea virginica have suffered major declines in the Gulf of America during recent decades, prompting for the development of aquaculture in the region. In 2019, a breeding program was initiated to support the developing industry. The program employs a communal rearing approach where families are reared communally from fertilization to phenotyping and molecular pedigrees are used to estimate breeding values.
The first generation was produced in 2020 by crossing founders collected from 17 natural reefs across the Gulf from San Antonio Bay (Tx) to Cedar Key (FL). Each generation, family pools (60 to 102 dams and sires each generation) are generated by crossing males and females according to non-overlapping 2 x 2 minifactorial sets, and mixing the obtained families after fertilization. The pools are deployed on grow-out sites selected to represent high and low salinity conditions. Parents and offspring harvested at the end of the growout period are genotyped at a low (192 Single Nucleotide Polymorphism, SNP), or medium (5,000 SNP) density panel to infer pedigree and genomic relationships which are then applied to estimate genetic parameters and breeding values using animal mixed models.
Estimates of heritability of growth rate at low salinity ranged between 0.63 and 0.84 and were significantly higher than the estimate obtained at high salinity (0.38). Genetic correlations across environments for growth rate generated using a multi environment model were intermediate to high (range 0.62-0.99), indicating moderate genotype x environment interactions. The initial generation revealed differential survival of families at high and low salinity sites. Selection was subsequently conducted separately for performance in high and low salinity environments. Parents with highest breeding values for growth rate were bred in 2022 and 2024 to generate F2 and F3 generations. Selected offspring grew faster than controls in the high and low salinity sites during evaluation of the F2 in 2023. Selected oysters also showed higher survival than controls at the 3 (out of 4) sites where mortality occurred, indicating positive response to selection on growth and correlated increase of survival. Data obtained during field testing of the F3 (second generation of selection) are in processing. Initial results indicate that the selected F3 generation grew faster than the control line at the two high-salinity sites; Survival was higher in the selected group at one site but lower in the second. Evaluation of the low salinity F3 generation was impacted by the summer mortality events observed in 2025 across the central Gulf of America. One low salinity site experienced over 91% mortality (both control and selected). The other sites available showed either similar performance of selected and controls when overall mortality was moderate, or a better performance of the control line when mortality was higher.