First record of a pearlfish, <I>Carapus mourlani</I>, inhabiting the Aplysiid Opisthobranch mollusc <I>Dolabella auricularia</I>

Abstract

Adult individuals of the pearlfish <I>Carapus mourlani</I> (Petit, 1934) occur commonly in the mantle cavity of the opisthobranch mollusc <I>Dolabella auricularia</I> (Lightfoot, 1786) in shallow marine waters of the Gulf of Chiriquí, Pacific Panamá. Nearly 30% of the molluscan hosts collected during the day on a coral reef contained one or two fish. Feeding observations of a captive fish as well as the intact condition of the host&#39;s ctenidium and other internal organs suggest that <I>C. mourlani</I> is an inquiline commensal and not parasitic. Fish curl around the ctenidium during the day and capture microcrustaceans when the fish emerge from their host at night to feed. From low-light infrared video recordings, <I>Carapus</I> was observed to accurately grasp rapidly swimming amphipods in nearly total darkness and ingest them. This symbiotic relationship appears to benefit <I>Carapus</I> by allowing the fish to avoid predators during the day and to forage at night.