Host recognition and possible imprinting in the anemonefish Amphiprion melanopus (Pisces: Pomacentridae)

Many reef fish have strong microhabitat preferences when they settle to the juvenile population, and choices at this time may influence fish survival. This is exemplified in anemonefishes (Family: Pomacentridae) that exhibit obligate symbiotic relationships with a restricted range of sea anemone species. This study examined how juvenile anemonefish Amphiprion melanopus select their host, and whether recognition and selection are mediated by an imprinting-like mechanism. Specifically, we experimentally examined the host-selection made by A. melanopus that had been reared under constant conditions, but whose embryos had received 1 of 3 treatments: (1) in contact with a known natural host sea anemone, Entacmaea quadricolor; (2) in contact with the sea anemone Heteractis malu, which is not a host for A. melanopus in nature, but is a host for anemonefish of other species; and (3) without a sea anemone (or chemical cues released from sea anemones) at any life stage. Our study shows that olfaction, not vision, is used by juvenile A. melanopus to recognize host anemones. Furthermore, the choice of a settlement site for juvenile A. melanopus is strongly influenced by events that occur early in development, prior to the dispersal of larvae from their natal site; We suggest that juvenile A. melanopus possess an innate preference for E. quadricolor, a preference that is enhanced by imprinting. Interestingly, it was not possible to imprint A. melanopus larvae to the non-host sea anemone H. malu, which suggests that anemonefish host-imprinting may be rather restricted.