ADVANCES IN C. virginica BREEDING IN CHESAPEAKE BAY, USA:  FROM MASS TO FAMILY-BASED SELECTION

Beginning in 2004, ABC has been developing genetically distinct lines of oysters resistant to to the protozoan parasite Haplosporidium nelsoni (causing MSX disease) and to Dermo, caused by the protozoan Perkinsus marinus.  ABC's lines, initially derived from Mid-Atlantic and Louisina stocks, were subjected to mass selection for fast growth until 2012.  Data clearly showed the improvement of ABC lines over wild stocks both for survival and growth traits, especially in locations where disease was present.  Today, these lines are the basis of 95% of total production in the Chesapeake, almost 90% of that is used for triploid oyster production.  

Family-based breeding approaches began in paralell to ABC's mass selection program in 2004 with the spawning and testing of full-sib families at two field locations.  In 2011-2013, a collaborative project with CSIRO in Australia established a bioeconomic model and associated weights of the traits most desirable to the Virginia industry.  Data from 2004-2010 year class families were analyzed to calculate heritabilities and genetic correlations for those traits.  Genetic variation for survival, total weight, width index (roundness), cup index (shell depth) and meat yield were found to be sufficiently high to warrant inclusion of all as part of the breeding objective, and the data suggests that substantial improvement in C. virginica is likely using family selection.

ABC has moved from an era of mass selection to a more refined, multi-trait, family-based breeding approach.  Progeny testing of 130 full-sib families produced each year occurs at four field locations (two low salinity/low disease, two moderate salinity/high disease), spanning 8-24ppt.  After completion of field testing, estimated breeding values (EBVs) of those traits described above are calculated using morphometric and pedigree data from the extant populations and past relatives.  Traits are weighted according to the economic value of each trait and an overall index value is calculated for each family. The top-ranked families are used as brood stock both for the creation of new families the following year with the goal of maximizing genetic merit while keeping the rate of inbreeding within defined limits. Additionally, the very best families are crossed to produce terminal lines as a source of commercial brood stock for industry.