''Sewellia'' is a
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
fish
A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
in the family
Gastromyzontidae
The Gastromyzontidae are a family of loaches native to China and Southeast Asia, where typically found in streams and rivers with a fast current. The family includes about 137 species in eighteen genera
Genus (; : genera ) is a taxonomic ran ...
. They are commonly called hillstream loaches (a common name shared with family
Balitoridae
Balitoridae, the hillstream loaches or river loaches, is a family, of small fish from South, Southeast and East Asia. The family includes about 202 species. They are sometimes sold as "lizardfish" or (in Germany) "flossensaugers". Many of the spe ...
) and are found in
Laos
Laos, officially the Lao People's Democratic Republic (LPDR), is the only landlocked country in Southeast Asia. It is bordered by Myanmar and China to the northwest, Vietnam to the east, Cambodia to the southeast, and Thailand to the west and ...
and
Vietnam
Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about and a population of over 100 million, making it the world's List of countries and depende ...
.
[Kottelat, M. (2012)]
Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei).
''Raffles Bulletin of Zoology, Suppl. No. 26: 1-199.'' According to Roberts (1998) a possible defining characteristic of the genus ''Sewellia'' is their posterior pelvic valve is highly complex and different from other rheophilic loaches (loaches adapted to fast flowing water), their posterior pelvic valve involves the overlapping of the second to last ventrally exposed rays.
Adapted to high velocity streams, ''Sewellia'' have depressed body shapes that are laterally expanded, thus increasing their hydrodynamical properties and allowing them to better stay attached to rocks in swift current.
''Sewellia'' also have paired fins with a single simple ray and numerous branched rays allowing them to grip rocks in swift current.
Distribution
Fish in the genus ''Sewellia'' occur in the Sekong River, a tributary of the Mekong river. The Sekong river drains large parts of central and southeast Laos as well as southern Vietnam.
Habitat and ecology
''Sewellia'' are found in the rapids and riffles of steep gradient 'hill streams', hence the common name
Hillstream Loach
Balitoridae, the hillstream loaches or river loaches, is a family, of small fish from South, Southeast and East Asia. The family includes about 202 species. They are sometimes sold as "lizardfish" or (in Germany) "flossensaugers". Many of the spe ...
.
Due to their steep gradients these streams have high current velocities, ''Sewellia'' are known to inhabit streams with current velocities exceeding m/s in some habitats.
Sewellia feed mainly on micro to macro sized aquatic invertebrates that inhabit the
periphyton
Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs ( German "surface growth" or "overgrowth", ) refers to the ...
attached to submerged rocks.
Sexual dimorphism
''Sewellia'' are sexually dimorphic, males have soft elevated patches of fine tubercles on the anterior part of pectoral-fin rays 1-6, females do not.
''
Sewellia lineolata'' are common in the
aquaria trade, they are sexed based on differences in shape, at sexual maturity males tend to be more streamlined while females are somewhat broad; the beginning of the pectoral fins occurs at a much sharper angle in the male than females, females have pectoral fins that begin in a more rounded fashion (softer angle).
Species
There are currently 13 recognized species in this genus:
* ''
Sewellia albisuera''
Freyhof, 2003
* ''
Sewellia analis''
H. D. Nguyễn & V. H. Nguyễn, 2005
* ''
Sewellia breviventralis''
Freyhof & Serov, 2000
* ''
Sewellia diardi
''Sewellia diardi'' is a species of fish belonging in the Gastromyzontidae
The Gastromyzontidae are a family of loaches native to China and Southeast Asia, where typically found in streams and rivers with a fast current. The family includes a ...
''
T. R. Roberts, 1998
* ''
Sewellia elongata''
T. R. Roberts, 1998
* ''
Sewellia hypsicrateae''
Endruweit & T. D. P. Nguyễn, 2016 [Endruweit, M. & Nguyen, T.D.P. (2016)]
''Sewellia hypsicrateae'', a new species of loach from central Vietnam (Teleostei: Balitoridae).
''Ichthyological Exploration of Freshwaters, 27 (4): 297-301.''
* ''
Sewellia lineolata''
(Valenciennes
Valenciennes (, also , , ; ; or ; ) is a communes of France, commune in the Nord (French department), Nord Departments of France, department, Hauts-de-France, France.
It lies on the Scheldt () river. Although the city and region experienced ...
, 1846)
* ''
Sewellia marmorata''
Serov, 1996
* ''
Sewellia media''
H. D. Nguyễn & V. H. Nguyễn, 2005
* ''
Sewellia monolobata''
(H. D. Nguyễn & V. H. Nguyễn, 2006)
* ''
Sewellia patella''
Freyhof & Serov, 2000
* ''
Sewellia pterolineata''
T. R. Roberts, 1998
* ''
Sewellia speciosa
''Sewellia'' is a genus of fish in the family Gastromyzontidae. They are commonly called hillstream loaches (a common name shared with family Hillstream loach, Balitoridae) and are found in Laos and Vietnam.Kottelat, M. (2012)Conspectus cobitidum ...
''
T. R. Roberts, 1998
* ''
Sewellia trakhucensis''
H. D. Nguyễn & V. H. Nguyễn, 2005
Conservation status
*''Sewellia albisuera'' - IUCN Critically Endangered
*''Sewellia analis'' - IUCN Not Evaluated
*''Sewellia breviventralis'' - IUCN Critically Endangered
*''Sewellia diardi'' - IUCN Data Deficient
*''Sewellia elongata'' - IUCN Near Threatened
*''Sewellia hypsicrateae'' - IUCN Not Evaluated
*''Sewellia lineolata'' - IUCN Vulnerable
*''Sewellia marmorata'' - IUCN Endangered
*''Sewellia medius'' - IUCN Not Evaluated
*''Sewellia patella'' - IUCN Endangered
*''Sewellia pterolineata'' - IUCN Endangered
*''Sewellia speciosa'' - IUCN Least Concern
*''Sewellia trakhucensis'' - IUCN Not Evaluated
References
{{Taxonbar, from=Q11949615
Freshwater fish genera
Gastromyzontidae
Taxa named by Sunder Lal Hora