My research addresses the host-symbiont relationship between a coral reef fish, Siphamia versicolor, and the luminous bacterium, Photobacterium mandapamensis. Very little is known about the S. versicolor – P. mandapamensis association, as there is little information regarding the more than 400 other fish that form symbioses with luminous bacteria. With support from the NSF EAPSI grant, I was able to ask fundamentally important questions regarding fish harboring symbiotic luminous bacteria at the University of the Ryukyusâ€™ Sesoko Station in Okinawa, Japan during the summer months of 2011. Specifically, my research addressed whether the bacteria are essential for the survival and development of the fish, the role the bacteria play in tissue development of the fish, and how the symbiont is attained in nature. Study of the association between S. versicolor and P. mandapamensis has the potential to reveal significant insight into the mechanisms by which vertebrate animals acquire, accommodate, and function cooperatively with bacteria. Through experimental colonization of the light organs of the fish, I determined the timing and specificity of the onset of the symbiosis, as well as the mechanisms involved with acquiring the symbiont in nature by examining the homing behavior of the fish. I collected and cultured S. versicolor from reefs surrounding Sesoko Station, and cultured their larvae aposymbiotically (without their symbiont) through to juvenile stage. I also successfully experimentally colonized the light organs of the fish and determined the window of time when infection can occur. I observed fish in the wild and determined the timing of the use of their luminescence and quantified their homing behaviors using mark-recapture methods.