The squid-vibrio symbiosis exists naturally as a multi-strain symbiosis. High-throughput growth assays have been used to characterized the growth of individual strains of V. fischeri using optical density. A modified assay tracking differential fluorescence over time in mixed culture allows for the growth of individual strains to be tracked. This assay can be utilized to determine how individual strains grow in mixed culture and to identify potential synergistic or antagonistic effects of strains on growth.