User:Jdx84/Symphurus thermophilus

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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 to inhabit several widely dispersed locations in the western Pacific Ocean and occurs in great numbers. These flatfish are distinguished by the prominent dark crossbands on their brown eyed side, black abdominal cavity membrane lining known as the peritoneum, and white blind side. 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.

Taxonomy

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.

A cryptic species of Symphurus in the southern Tonga and Kermadec Arcs was previously described as S. thermophilus, however, recent research has suggested that it has a distinct genetic makeup compared to that of the S. thermophilus in the northern Mariana Arc, despite exhibiting comparable morphology and behavior.

Anatomy and morphology

Like other tonguefishes, S. thermophilus has a laterally flattened body with united dorsal, caudal, and anal fins. Two fairly large and rounded eyes are located on the left side of the head in adults. The pectoral fins and lateral line are absent, and there is only a single, right-side pelvic fin. The head is moderately long, with a blunt snout and long, broadly arched jaws. There are 4-5 rows of teeth on the upper and lower jaws of the blind side, and 2-3 and 1 rows on upper and lower jaws respectively of the eyed side. The teeth are sharp and recurved, and better developed on the blind-side jaws.

The body is notably deep compared to other Symphurus species. The origin of the dorsal fin is located above the eyes and contains 88-94 rays. The dorsal fin pterygiophores and neural spines have a 1-2-2-2-2 interdigitation pattern. The pelvic fin is moderately long, contains 4 rays, and is connected to the body by a delicate membrane. The anal fin contains 74-80 fin rays. The caudal fin is relatively long and contains 14 rays. The scales are small and strongly ctenoid in shape, numbering 47-56 rows transversely and 100-112 rows longitudinally.

Both adults and juveniles typically exhibit similar body coloration. The eyed side of the body is medium to dark chocolate brown in color, mottled with numerous dark, irregularly shaped blotches and white speckles, along with five to eight darker, complete or incomplete crossbands. Some individuals have a white patch over two-thirds of the abdominal cavity, sometimes exhibiting bluish-green tints and bordered posteriorly by a black blotch. The abdominal area posterior to the gill opening is blackish brown and much darker than the rest of the body. A conspicuous black membrane lining of the abdominal cavity, known as the peritoneum, is visible through its abdominal wall. Occasionally, there are one or two irregular to nearly circular white spots along the body midline. The fin rays are dark at the base and lighter towards the tips, and there is an irregular dark spot at the base of the caudal fin. The blind side of the body is white, with scattered dark melanophores.

The maximum known length is 8.7 cm for a male and 11.2 cm for a female. The fish from the Nikko Seamount are nearly twice as large as those from the Kasuga-2 and Daikoku Seamounts. This may be because of the higher biological productivity at Nikko, or because Kasuga-2 and Daikoku were recently colonized.

Biology and ecology

Feeding

S. thermophilus are particularly active in their search for infaunal prey on sediments. To create space in their stomachs for additional food intake, they expel any ingested sediment either via their gills or gut upon spotting their prey.

Based on the fatty acid composition and stable carbon isotope ratios in tissues of S. thermophilus found on the Mariana Arc, there is evidence that the fish ingest material that originated in the photic zone. At Daikoku seamounts, fatty acid composition of S. thermophilus suggest that food webs were more based on chemosynthesis than at other seamounts in the Mariana Arc.

Distribution and habitat

S. thermophilus surrounded by hydrothermally related bacterial mats taken during Leg 3 of the NOAA Okeanos Explorer Program's 2016 Deepwater Exploration of the Marianas.

Tonguefish were associated with three different substrata across the Daikoku, Kasuga-2, and Nikko seamounts. On the Daikoku and Kasuga-2 vents, the tonguefish were found on volcanoclastic and sulfuric sediments. In the Nikko vents, they were found among dense colonies of tubeworms. The fish were also associated with sheeted sulfur flows and conglomerates that were found near high temperature vents and sulfur. On outcrops of andesite and basalt that were untouched of venting, there were no tonguefish found. Of surfaces with dense microbial mats, tonguefish populations were noticably reduced.

The overall distribution of S. thermophilus are relatively dispersed. The highest abundances were found in pits of granular sulphur or volcanoclastic sediments. On the Daikoku vents, the abundance of fish was found to be 80 fish/m², which was calculated from around 150 non-overlapping images collected through remotely operated vehicles (ROVs) from 2005-2006.