EFFECTS OF MARINE-BACTERIA ON THE CULTURE OF AXENIC OYSTER CRASSOSTREA-GIGAS (THUNBERG) LARVAE

Bacteria-free oyster larvae (Crassostrea gigas) were cultured under aseptic conditions; they were fed axenic algae (Isochrysis galbana), and the medium was inoculated with isolated strains of marine bacteria. Twenty-one bacterial strains were tested, and most were detrimental to larval survival and growth. However, additions of strain CA2 consistently enhanced larval survival (21-22%) and growth (16-21%) in comparison with control cultures that were fed only algae. Size-frequency distributions of populations of larvae cultured for 10 days on axenic algae were skewed due to the poor growth of many individuals; whereas size-frequencies from populations of larvae fed axenic algae supplemented with CA2 bacteria were distributed normally. Strain CA2 may therefore make a nutritional contribution to the growth of oyster larvae. I. galbana did not grow under the light intensities used for larval culture; thus the improvement in larval growth cannot be attributed to bacterial enhancement of algal growth and, consequently, food availability. Naturally occurring microflora from Yaquina Bay, Oregon, depressed survival or growth of larvae-fed live algae.