Abstract

BSTRACT: A Vibrio anguillarum-related (VAR)strain, isolated in pure culture from an epizootic in a commercial hatchery producing Argopecten purpuratus, was characterized, and its potential patho- genicity to veliger larvae of A. purpuratus determined. Experimental challenges indicated that the bac- terium affects larval survival at concentrations of 104 to 108 cells ml-l The effect of water quality and temperature on pathogenicity was also evaluated. Larval survival in seawater filtered through 5 pm pore-size membranes was 45.6%, whereas using seawater passed through 1 and 0.2pm filters, larval survival increased to 66.4 and 80.4% respectively. Temperature also affected pathogenicity as larval survival at 15OC for 24 h was 69.3% but decreased to 30 and 26.9% at 20 and 25°C respectively. Toxic activity was found in cell-free supernatant of bacterial culture. Larval survival was reduced to 68.9and 36.4% after 20 and 40% (v/v) of supernatant, respectively, was added to the rearing water. These results suggest that exotoxins produced by the VAR strain play an in~portantrole in its pathogenicity for scallop larvae.