A total of 312 P. vannamei shrimp DNA samples were used in this study. A
description of the six populations used can be found in Table 1. The criteria used for
classifying populations as specific pathogen free (SPF) or high health is described in
Lotz et al. (1995). DNA was extracted from tail muscle or pleopods following the
procedure of Alcivar et al. (1989) with modifications by Garcia et al. (1994).