Symbiotic cleaning relationship between a sailfish (Istiophorus platypterus) and remoras (Remora osteochir)

Abstract The symbiotic relationship between remoras and their hosts is difficult to comprehensively evaluate, as hosts may experience both benefits and disadvantages from their interaction with remoras. This study observed behaviors of sailfish ( Istiophorus platypterus ) and marlin suckers ( Remora osteochir ) in an aquarium by filming them. The marlin suckers displayed cleaning behavior, inserting their heads into small depressions along the base of the sailfish's fins and pecking at the host's injured snout. In response, the sailfish reduced its swimming speed and opened its operculum, allowing the marlin sucker to exit the gill cavity. These behaviors were consistent with the typical "cleaning–request" behavior observed in host species interacting with cleaner fish. Our observations strongly suggest a symbiotic relationship between the two species. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo250502ip07a , http://www.momo-p.com/showdetail-e.php?movieid=momo250502ip09a , and http://www.momo-p.com/showdetail-e.php?movieid=momo250502ip05a .