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

Abstract

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.