Commensalism between a liparid fish (Careproctus sp.) and stone crabs (Lithodidae) photographed in situ using a baited camera

Abstract

The commensal relationship between a snailfish, tentatively identified as Careproctus sp. (Osteichthyes: Liparidae), and the lithodid crab Paralomis formosa (Crustacea: Lithodidae) was photographed in situ using a baited camera vehicle, deployed at depths of 625-1525 m around Shag Rocks and South Georgia in the Southern Ocean. The series of time-lapse photographs taken clearly showed that the small liparid fish `hitched rides' on the crabs, presumably attaching to the dorsal carapace and legs of the crabs by means of their ventral sucking disk. Liparid fish of 20-90 mm total length, corresponding to juveniles and adult sizes, were observed on the crabs and indicate that Careproctus sp. is closely associated with P. formosa for the whole of the life cycle of the fish. Such an association may provide the snailfish with protection from potential predators as well as a means of transport towards food-falls but at no apparent cost to the crabs.