Heritability estimates of disease resistance to Vibrio coralliiyticus in Pacific oyster (Crassostrea gigas) larvae from a selective broodstock program

Marine bivalves account for roughly 14% of aquaculture production worldwide and ca. 33% of this production is represented by oysters. A number of disease-causing agents of oysters have the potential to create economic loss to shellfish farmers. Disease outbreaks due to Vibrio coralliiyticus are considered to be a major problem in the hatchery production of bivalve larvae and juveniles (spat). An effective management strategy in preventing disease in bivalves is to produce genetically resistant families. Since 1996, researchers from Oregon State Uni-versity's Molluscan Broodstock Program (MBP) have bred and selected families of Pacific oysters (Crassostrea gigas) with greater growth, yield, and survival at harvest compared to wild C. gigas; however, there has been no experimental assessment of the MBP families' resistance to Vibrio coralliiyticus. The progeny of 89 MBP families were challenged with V. coralliiyticus in a microplate assay. Larval survival was assessed over a seven-day period with independent time points using image analysis, which reconstructed the contents of each well. The narrow sense (h2) heritability of disease resistance for MBP oyster larvae to V. coralliiyticus was determined with a linear mixed effects model, known as the animal model. After accounting for the influence of fixed and random effects (time point, animal, and plate well), the estimate of heritability of survival (h2) was detectable on both the latent (0.535-0.541) and observed scales (0.113-0.114). The low heritability estimates on the observed scale suggest that enhancement of MBP's oyster larvae's resistance to V. coralliiyticus through selective breeding is expected to take multiple generations. Estimating the heritability of C. gigas to V. coralliiyticus may have been complicated by the life stage examined, the dynamics of V. coralliiyticus infection, and uncontrolled environmental factors in the well plate assays.