NOTE Cues from the reef: olfactory preferences of a symbiotically luminous cardinalfish Alison L. Gould • Saki Harii • Paul V. Dunlap Received: 11 October 2014 / Accepted: 20 February 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract The symbiotically luminous, reef-dwelling cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), exhibits daily site fidelity, homing behavior, and a prefer- ence 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. seto- sum. Juvenile fish, but not adults, preferred seawater con- ditioned 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 set- tlement and symbiont acquisition, but not for host urchin recognition. Keywords Siphamia tubifer  Apogonidae  Olfaction  Homing  Bioluminescence  Symbiosis Introduction Cardinalfishes (Apogonidae) display strong site fidelity and homing ability through navigation using a combination of auditory, visual, and chemical cues (Marnane 2000; Kolm et al. 2005; Døving et al. 2006; Fukumori et al. 2010; Gardiner and Jones 2010; Gould et al. 2014). Olfaction, in particular, plays an important role for both larval and adult fish returning to reefs, with various chemical cues known to indicate habitat quality (Atema et al. 2002; Dixson et al. 2010, 2011, 2014; Døving et al. 2006; Gerlach et al. 2007; Coppock et al. 2013). Adult apogonids have strong olfac- tory abilities, distinguishing between the odors of con- specifics from a home reef and those from a foreign reef (Døving et al. 2006), and larval apogonids use olfactory cues for settlement, sometimes to a reef of origin (Atema et al. 2002; Gerlach et al. 2007). Analysis of the use of olfactory cues can therefore provide insight into how fish recognize and navigate to their daytime resting sites, identify suitable settlement habitat, and return to natal reefs. The sea urchin cardinalfish, Siphamia tubifer, inhabits coral reefs in the Indo-Pacific and aggregates in groups by day among the spines of sea urchins, particularly the long- spined sea urchin, Diadema setosum. Early in develop- ment, S. tubifer initiates a symbiosis with the luminous bacterium, Photobacterium mandapamensis, which it ac- quires from the environment (Dunlap et al. 2012). The bacteria establish a large, light-producing population in an abdominal light organ that connects to the intestine; the fish uses the bacterial light to illuminate its ventrum while Communicated by Biology Editor Dr. Andrew Hoey Electronic supplementary material The online version of this article (doi:10.1007/s00338-015-1278-y) contains supplementary material, which is available to authorized users. A. L. Gould (&)  P. V. Dunlap Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University Avenue, Ann Arbor, MI 48109, USA e-mail: algould@umich.edu S. Harii Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Motobu, Okinawa 905-0227, Japan 123 Coral Reefs DOI 10.1007/s00338-015-1278-y