Cues from the reef: olfactory preferences of a symbiotically luminous cardinalfish

The symbiotically luminous, reef-dwelling cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), exhibits daily site fidelity, homing behavior, and a preference for the long-spined urchin, Diadema setosum , as its daytime host. The fish acquires its symbiont during larval development and releases large numbers of the bacteria with its feces daily at a host urchin. To examine the role of olfaction in site fidelity and homing by S. tubifer , juvenile and adult fish were tested in a two-channel choice flume for their olfactory preferences. Neither juveniles nor adults showed a preference for seawater conditioned by D. setosum . Juvenile fish, but not adults, preferred seawater conditioned by conspecific fish versus unconditioned seawater. Both juveniles and adults preferred seawater conditioned by their luminous symbiont and also preferred home site water to foreign reef water. These results suggest that S. tubifer uses chemical cues for homing and possibly settlement and symbiont acquisition, but not for host urchin recognition.