Protease inhibitory activity in selectively bred families of eastern oysters

In an effort to identify potential biochemical markers for resistance to De rmo, a disease that afflicts eastern oysters Crassostrea virginica, selecte d stocks of these oysters were interbred to produce 10 families with high i nterfamily and intrafamily genetic variability; subsamples of 2-year-old oy sters from each family were then assessed for protease inhibitory (PI) acti vity against proteases of Perkinsus marinus, the causative agent of Dermo. The prevalence and intensity of the pathogen were determined via Ray's flui d thioglycollate medium test. Family survival under field challenge, diseas e intensity, and PI activity were compared to evaluate family performance. In the laboratory, three families had the highest survival rates, lowest av erage numbers of parasite cells, and highest average PI activity. In field challenges, the same three families exhibited the lowest cumulative mortali ty. Among all families, disease intensity was negatively correlated with PI activity; mortality patterns also indicated an inverse relationship betwee n disease intensity and such activity.