Ninety-nine strains of attached bacteria were isolated from settlem-ent substratum of larvae of Argopecten irradians L. in hatchery tanks. The bacteriawere identified and classified into nine genera, including Vibrio, Pseudomonas,Achromobacter, Bacillus, Aeromonas, Staphalococcus, Micrococcus, Corynebacterium and Flavobacterium. After the settlement of larvae, the bacteria isolated from subs- tratum were all Gram's negative rods. The settlement of larvae need certain amountof attached bacteria on the surface of substratum. Experiments with single-species'films indicated that individual bacteria strain varied in their capacity in inducingsettlement of larvae. Some bacteria strains could induce seventy-six percent morelarvae to settle than none film's control, while others failed to induce settlementof Larvae, or even inhibited the process