Response to selection and estimation of heritabilities for rapid growth in eastern oysters (Crassostrea virginica, Gmelin 1791) and the use of fast growing lines to reduce susceptibility to juvenile oyster disease

As shellfish farmers become increasingly dependent upon hatchery-reared seed, the use of selected broodstock lines is becoming an important means of improving production traits such as growth rate and resistance to disease. Bivalve molluscs are well suited to selection programs due to their high fecundity, relatively short generation interval, and high phenotypic variation in wild populations.; Production performance in terms of growth and survival were assessed in three lines of eastern oysters selected fro rapid growth. Response to selection was positive in first generation selected progeny for all lines. Realized heritabilities for live weight ranged from 0.31 to 0.58. Narrow-sense estimates of heritability for growth traits were determined for both selected and control sub-lines. Sire-based estimates of heritability for larval shell length were 0.44 (+/-0.14) and 0.14 (+/-0.07) in the selected and unselected control sub-lines, respectively. Corresponding estimates for live weight at 7 months were 0.51 (+/-0.15) and 0.10 (+/-0.05), respectively. Assessment of genetic variation (using allozymes) revealed that selected sub-lines were generally less heterozygous than corresponding control sub-lines.; Recurring mortalities of hatchery-reared juvenile oysters, caused by Juvenile Oyster Disease (JOD), prompted a monitoring program to track growth and survival of juvenile eastern oysters. JOD induced cumulative mortality was highly correlated to mean cohort size (shell height). Sub-lines selected for rapid growth when challenged by the JOD pathogen, had consistently improved survivability compared to unselected controls.; Use of high performance lines will have obvious benefits to shellfish breeders and mariculturists by reducing the growing period required to reach market size and possibly improving hardiness as a correlated response.