Protease inhibitory activity in selectively bred families of eastern oysters.

Abstract In an effort to identify potential biochemical markers for resistance to Dermo, a disease that afflicts eastern oysters Crassostrea virginica, selected stocks of these oysters were interbred to produce 10 families with high interfamily and intrafamily genetic variability; subsamples of 2-year-old oysters from each family were then assessed for protease inhibitory (PI) activity against proteases of Perkinsus marinus, the causative agent of Dermo. The prevalence and intensity of the pathogen were determined via Ray's fluid thioglycollate medium test. Family survival under field challenge, disease intensity, and PI activity were compared to evaluate family performance. In the laboratory, three families had the highest survival rates, lowest average numbers of parasite cells, and highest average PI activity. In field challenges, the same three families exhibited the lowest cumulative mortality. Among all families, disease intensity was negatively correlated with PI activity; mortality patterns also i...