The mutualism between Euprymna scolopes and Vibrio fischeri presents a model through which host-microbe interactions can be studied to provide insight into mechanisms that microbes utilize to colonize the host. In this investigation, the phenotypes of two co-isolated V. fischeri strains were determined using bioluminescence and motility assays. Novel V. fischeri strains, RB003 and JDS004, showed dissimilar phenotypes when compared to wild-type ES114, suggesting certain strains have a greater capability to colonize the host.