page_title: Symphurus thermophilus
section_title: Biology and ecology
hierarchical_section_title: Symphurus thermophilus / Biology and ecology
caption_attribution_description: English: Tonguefish (Symphurus thermophilus) and crabs on the seafloor at the Daikoku Seamount. The lasers (red dots) are 10 cm apart.
context_page_description: Symphurus thermophilus is a species of tonguefish notable for being the only flatfish known to be an obligate inhabitant of hydrothermal vents. It is known from several widely dispersed locations in the western Pacific Ocean and occurs in great numbers. They are tolerant of harsh conditions and are often found in close association with elemental sulfur, including molten sulfur pools that exceed 180 °C in temperature. As they are not significantly different in appearance and feeding habits from other tonguefishes, they are thought to be relatively recent colonizers of vent ecosystems.
  These fish were first observed in nature in 1988, and were provisionally assigned to the species Symphurus orientalis before being recognized as a new species. The species name thermophilus is from the Greek thermos meaning "heat" and philos meaning "lover", referring to its association with hydrothermal vents.
context_section_description: S. thermophilus spend most of their time on the sea floor, moving forwards or backwards by undulating their bodies and sometimes burying themselves completely in the substrate. They seem to be attracted to loose sediments, probably related to the uncovering of food, and often congregate in pits. The fish frequently rest atop one another without reaction.
  The vent communities that co-occur with S. thermophilus differs greatly between seamounts. They co-occur with large numbers of the snail Oenopota ogasawaarna at the Daikoku Seamount, and with the abundant shrimp Opaepele loihi at the Nikko Seamount. They also frequently occur with the crab Austinograea yunohana, which are found at Nikko, Daikoku, and Kasuga-2. Large bythograeid crabs have been observed attempting attacks on the fish, though not successfully. S. thermophilus likely experiences little to no predation pressure, which coupled with the high food biomass available allows their high densities.
  The affinity of this species for native sulfur has yet to be explained. The morphology of S. thermophilus does not show any differences from other deepwater Symphurus species that would suggest adaptations to its unique habitat. However, S. thermophilus likely possesses extensive physiological and biochemical adaptations for coping with the harsh conditions around hydrothermal vents, such as temperature and pH fluctuations, and exposure to heavy metals. In particular, they must have high hemoglobin oxygen affinities and efficient respiratory systems to deal with the toxic hydrogen sulfide in venting fluid. S. thermophilus is also capable of tolerating pH as low as 2, akin to sulfuric acid, and can rest over pools of molten sulfur without harm. Individuals of S. thermophilus often show skeletal abnormalities such as undeveloped fin rays or fused bones, likely attributable to the vent environment.
caption: S. thermophilus with bythograeid crabs around a "sulfur cauldron" at the Daikoku Seamount.
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