Association of Aeromonas hydrophila and Vibrio alginolyticus with Larval Mortalities of Scallop (Argopecten purpuratus)

A bacteriological study was carried out in a hatchery of Argopecten purpuratus located in northern Chile which had been affected by severe larval mortalities. The phenotypic characterization of the bacterial strains revealed that Vibrio alginolyticus was the predominant species isolated in the majority of samples taken from the different units of the hatchery (microalgae, swimming larvae, seawater of larval culture tanks, and a reservoir tank of 50-μm filtered seawater). However, the bacterial population of dying larvae was composed of only Aeromonas hydrophila strains which proved to be resistant to most of the chemotherapeutic agents tested. The bioassays conducted to evaluate the effect of these bacteria on larval survival showed that all of the isolated Vibrio and Aeromonas strains possessed a high degree of pathogenicity, since they produced dying larvae on concentrations ranging from 5.5 x 10(4) to 5.5 x 10(2) cells/ml. The possible virulence mechanism of these bacteria is discussed, as well as the potential use of drugs to prevent larval mortalities.