Abstract
Symbiotic relationships between fishes and other organisms are not always easily defined, and three-way symbiotic relationships are rarely reported. Here we examine the relationship between the endangered whale shark, echeneids (remoras and sharksuckers) and a symbiotic copepod. Through their symbiosis with whale sharks, sharksuckers gain one food source from the host’s parasites and energetically-free transportation to foraging areas, where they are also able to feed on the prey targeted by their hosts. The relationship between whale sharks and sharksuckers is complex, and most accurately described as mutualism. Likewise, the whale shark and copepod relationship is also complex, and could be described as a parasitic relationship with commensal or even mutualistic characteristics. Although echeneids are not considered to form host-specific relationships and can be free-ranging, the whale shark copepod occurs only on whale sharks; its survival inextricably linked to that of its host.
Highlights
Symbiosis – whereby two species live together – is common in fishes, and can include parasitism, mutualism, and commensalism (Helfman et al 2009)
Both whale shark copepods and echeneids have developed uniquely different morphologies and mechanisms to cope with the substantial drag forces associated with living in a symbiosis with the world’s largest fish
Considering that whale sharks are globally listed as endangered (Pierce and Norman 2016), it may be prudent to recognise the whale shark copepod as endangered. This highlights the need for symbiotic relationships to be considered in conservation planning to ensure the maintenance of healthy ecosystems (Lymbery et al 2020). Through their symbiosis with whale sharks, echeneids gain one food source from the host’s parasites and energetically-free transportation to areas where they can forage on another food source (Video S1)
Summary
Symbiosis – whereby two species live together – is common in fishes, and can include parasitism, mutualism, and commensalism (Helfman et al 2009). There is a general consensus that members of the Echeneidae (remoras and suckerfishes), which are recognised by having a spinous dorsal fin uniquely modified into a large anteriorlyplaced oral adhesive disc (Britz and Johnson 2012), have a mutualistic relationship with their hosts, including whale sharks (Fig. 1). Members of this family have been found to have a high proportion of parasitic (or commensal) copepods in their diet which they remove from the bodies of their hosts (Cressey and Lachner 1970). Journal compilation Ó CSIRO 2021 Open Access CC BY www.publish.csiro.au/journals/pcb
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