Pseudexostoma
Encyclopedia
Pseudexostoma is a genus
of catfish
es (order
Siluriformes) of the family
Sisoridae
. It includes three species
, P. brachysoma, P. longipterus, and P. yunnanensis.
(Nujiang River) and one upper branch of the Irrawaddy
(Dayinjiang) in China
. P. brachysoma is known only from the middle and lower Nujiang River. P. longipterus is known only from the middle Nujiang River. P. yunnanensis is only known from the upper Dayinjiang (an upper branch of the Irrawaddy River. These rivers were once connected, but are now separated. Also, the environment and temperature of the Nujiang River became greatly different between the northern and southern areas, leading to speciation.
openings not extending onto the underside (venter), heterodont
dentition in both jaws with outer teeth shovel-shaped and sparsely arranged in one or two rows and inner teeth conical and numerous, the tooth patches separated in upper jaw, and 16–18 branched pectoral rays. The lips are thick, fleshy, and papilla
ted. The paired fins are plait
ed to form an adhesive apparatus.
Pseudexostoma species have a moderately compressed body. The head is depressed and broad; it appears triangular from the side and with a rounded snout from above. The eyes are small and ovoid, located at the middle of the dorsal surface of the head. The mouth is transverse and inferior, with the teeth exposed when the mouth is closed. The teeth are embedded in the skin, shovel-shaped, with the tips exposed and arranged in irregular rows. The gill openings are narrow. The dorsal surface is smooth without tubercle
s. There are four pairs of barbels
. The adipose fin base is not connected to the caudal fin. The caudal fin is emarginate with the upper lobe smaller than the lower lobe. The lateral line
is midlateral and complete.
Pseudexostoma species are grey black on the dorsal surface and grey yellow on the ventral region; the caudal fin is grey black with an irregular, small, yellow patch in the middle, and the other fins are grey yellow along the distal edge. Pseudexostoma grow to about 9.9–15.3 centimetres (3.9–6.0 in) SL
.
Pseudexostoma species have three notches on the posterior margin of the lower lip. However, in P. yunnanensis, the notches are all the same depth, while in the other two species the middle notch is shallower in depth than the lateral notches. The two median lobes formed by these notches are the same length of the lateral lobes of the lips in P. yunnanensis, but they are longer in the other two species. P. yunnanensis also has more pelvic fin rays (5 vs. 3–4), a shorter adipose fin base, a deeper and longer caudal peduncle, more teeth in the premaxilla
ry tooth band (18–22 vs. 16–18) that are divided into two partially connected patches instead of two isolated patches. Between P. brachysoma and P. longipterus, P. longipterus has longer pectoral fins, pelvic fins, and caudal fins as well as large eyes that are farther apart than in P. brachysoma.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of catfish
Catfish
Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
es (order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Siluriformes) of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Sisoridae
Sisoridae
Sisoridae is a family of catfishes . These Asian catfish live in fast-moving waters and often have adaptations that allow them to adhere to objects in their habitat.-Taxonomy:...
. It includes three species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, P. brachysoma, P. longipterus, and P. yunnanensis.
Taxonomy
Glyptosternum yunnanesis was first described in 1935. However, due to its unique teeth, a separate genus Pseudexostoma was erected in 1979 for this species. The same year, a subspecies of P. yunnanensis was described, P. y. brachysoma. However, it has become apparent that these two groups represent different species. Also, a third species, P. longipterus, was described in 2007.Distribution
Pseudexostoma species are restricted to the upper SalweenSalween River
The Salween is a river, about long, that flows from the Tibetan Plateau into the Andaman Sea in Southeast Asia. It drains a narrow and mountainous watershed of that extends into the countries China, Burma and Thailand. Steep canyon walls line the swift, powerful and undammed Salween, one of the...
(Nujiang River) and one upper branch of the Irrawaddy
Ayeyarwady River
The Irrawaddy River or Ayeyarwady River is a river that flows from north to south through Burma . It is the country's largest river and most important commercial waterway. Originating from the confluence of the N'mai and Mali rivers, it flows relatively straight North-South before emptying through...
(Dayinjiang) in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. P. brachysoma is known only from the middle and lower Nujiang River. P. longipterus is known only from the middle Nujiang River. P. yunnanensis is only known from the upper Dayinjiang (an upper branch of the Irrawaddy River. These rivers were once connected, but are now separated. Also, the environment and temperature of the Nujiang River became greatly different between the northern and southern areas, leading to speciation.
Description
Pseudexostoma species have a continuous groove behind the lip (post-labial groove), gillGill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
openings not extending onto the underside (venter), heterodont
Heterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...
dentition in both jaws with outer teeth shovel-shaped and sparsely arranged in one or two rows and inner teeth conical and numerous, the tooth patches separated in upper jaw, and 16–18 branched pectoral rays. The lips are thick, fleshy, and papilla
Papilla (fish mouth structure)
The papilla, in certain kinds of fish, particularly rays, sharks, and catfish, are small lumps of dermal tissue found in the mouth, where they are "distributed uniformly on the tongue, palate, and pharynx"...
ted. The paired fins are plait
Plait
A plait may refer to:* Plait, also called a braid, intertwined strands of, for example, textile or hair* Plait, now called a pleat, a fold of fabric, used in clothing and upholstery* Plait , a fold in the columella of a gastropod mollusc...
ed to form an adhesive apparatus.
Pseudexostoma species have a moderately compressed body. The head is depressed and broad; it appears triangular from the side and with a rounded snout from above. The eyes are small and ovoid, located at the middle of the dorsal surface of the head. The mouth is transverse and inferior, with the teeth exposed when the mouth is closed. The teeth are embedded in the skin, shovel-shaped, with the tips exposed and arranged in irregular rows. The gill openings are narrow. The dorsal surface is smooth without tubercle
Tubercle
A tubercle is generally a wart-like projection, but it has slightly different meaning depending on which family of plants or animals it is used to refer to....
s. There are four pairs of barbels
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
. The adipose fin base is not connected to the caudal fin. The caudal fin is emarginate with the upper lobe smaller than the lower lobe. The lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
is midlateral and complete.
Pseudexostoma species are grey black on the dorsal surface and grey yellow on the ventral region; the caudal fin is grey black with an irregular, small, yellow patch in the middle, and the other fins are grey yellow along the distal edge. Pseudexostoma grow to about 9.9–15.3 centimetres (3.9–6.0 in) SL
Fish measurement
Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...
.
Pseudexostoma species have three notches on the posterior margin of the lower lip. However, in P. yunnanensis, the notches are all the same depth, while in the other two species the middle notch is shallower in depth than the lateral notches. The two median lobes formed by these notches are the same length of the lateral lobes of the lips in P. yunnanensis, but they are longer in the other two species. P. yunnanensis also has more pelvic fin rays (5 vs. 3–4), a shorter adipose fin base, a deeper and longer caudal peduncle, more teeth in the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
ry tooth band (18–22 vs. 16–18) that are divided into two partially connected patches instead of two isolated patches. Between P. brachysoma and P. longipterus, P. longipterus has longer pectoral fins, pelvic fins, and caudal fins as well as large eyes that are farther apart than in P. brachysoma.