Remora

Remora remora is a fish of the family Echeneidae, whose members travel attached to other marine animals by an adhesive disc derived from the dorsal fin ^[1]. Its accepted scientific name is Remora remora (Linnaeus, 1758) ^[2]. It is a pelagic specialist: it has been recorded with about 30 different hosts, mostly sharks and mobulids ^[3]. Its global IUCN category is Least Concern ^[4].

It is dark brownish grey, with no spines in the dorsal or anal fins; it has 22 to 26 dorsal soft rays and 22 to 24 anal rays, and a maximum recorded length of 86.4 cm ^[5].

The anterior dorsal fin has become a suction disc. In the remoras studied, the disc holds up to 26 pectinated lamellae arranged on both sides, and rows of thin spinules on them touch the host surface ^[6].

The fleshy rim of the disc carries putative push-rod mechanoreceptor complexes. In this species 17 to 24 per cm² were counted on the anterior part of the rim and 11 to 15 per cm² on the posterior part ^[1].

Similar species

• Echeneis naucrates: Remora remora has a deeper body than Echeneis naucrates ^[5]. Also, in the southwest Atlantic Echeneis naucrates turned up along the coast as well as at oceanic islands, whereas Remora remora was found only around offshore islands and in the open sea ^[7].

It is cosmopolitan in warm waters, between 60° N and 36° S, and is listed with a depth range of 0 to 200 m ^[5].

That depth limit falls short when the host dives. Off Santa Maria island in the Azores, a remora rode a whale shark down to 1460 m, where the water was at 3.6 °C, during a dive in August 2020. The maximum depth confirmed before was 140 m ^[3].

Records from the southwest Atlantic come only from oceanic islands and the open sea, none from the coast ^[7].

It feeds on parasitic copepods ^[5].

To attach, the fish touches the host skin and rotates the lamellae of the disc: the spinules create friction and a pressure below ambient seals the fleshy lip ^[1].

It is associated with about 30 hosts, most often sharks and mobulids ^[3]. In the Maldives, a mean of 1.5 ± 0.5 individuals per sighting was counted with the oceanic manta, and remoras were more likely to be present with females ^[8].

In the Galapagos it is seen on almost all whale sharks sighted in the islands ^[9].

It is also associated with sea turtles: in the southwest Atlantic two remora species were recorded on four sea turtle species, although the association seems rare there ^[7].

Who gains from the association remains debated: the remora saves transport energy and gets protection and food, but it can cause drag and skin abrasion on the host, so the relationship may be mutualistic, commensal or antagonistic depending on the case ^[3].

The IUCN classifies it globally as Least Concern, based on the 2012 assessment ^[4].

CITES has not evaluated it ^[5].

It is caught commercially and counted as a game fish; it is not dangerous to people ^[5].

Its attachment mechanism has driven the development of bio-inspired technological solutions ^[3].