Some bacteria have competition mechanisms used to eliminate competitors like the type VI secretion system (T6SS), a molecular needle that can inject toxins into neighboring cells. In the context of diverse bacterial symbionts, the T6SS can have potential impacts on symbiont diversity. To study how co-isolated symbionts are able to colonize one host when some encode T6SSs, we determined their colonization frequencies and their compatibility on solid media and introduced juvenile squid to co-isolated strains.