Cetopsidium
Encyclopedia
Cetopsidium is a genus
of catfish
es (order
Siluriformes) of the family
Cetopsidae
. It includes seven species, C. ferreirai, C. minutum, C. morenoi, C. orientale, C. pemon, C. roae, and C. soniae.
, the first described cetopsid genus, and idium which means dimunutive, in reference to the relatively small size of Cetopsidium species. Three existing species were transferred to this genus and three new species were described. In 2009 a new species, Cetopsidium soniae, was described bringing the number of species in the genus to seven.
. C. minutum occurs in the Potaro River
and middle portion of the Essequibo River
of Guyana
. C. morenoi is known from the central and western portions of the Orinoco
River basin in Venezuela
and Colombia
. C. orientale is known from the coastal rivers of Suriname and French Guiana
in the region from the Corantijn River along the border between Suriname and Guyana to the Oyapock
-Oiapoque River along the French Guiana-Brazil
border; it is likely this species is also occurs in the left bank tributaries to the Corantijn River draining from Guyana and the Oiapoque River in Brazil. C. pemon is known from the Caroni River
and the Caura River
basins, southern tributaries of the Orinoco in eastern Venezuela, the Meta River
basin of the western portions of the Orinoco system in eastern Colombia, and the upper portions of the Branco River
in northern Brazil. C. roae is only known from the Rupununi
region of southwestern Guyana
.
with an ossified spinelet and the presence of pectoral-fin and dorsal-fin
spines distinguishes the species of Cetopsidium from all other genera in the Cetopsinae. A lateral line
extending to over the posterior portion of the base of the anal fin but falling short of the caudal peduncle is also unique in this genus; the lateral line is usually longer than this, though it is shorter in two species of Denticetopsis
. Cetopsidium species have mental barbels
extending posteriorly beyond the rear margin of the opercle
and a deeply-forked, symmeterical caudal-fin margin with the tips of the lobes slightly blunt or rounded.
The body is elongate to moderately robust; anteriorly the body is not compressed much, but becomes progressively compressed posteriorly. The lateral line is incomplete, unbranched, and midlateral. In most species the dorsal profile is straight, though it may be slightly convex from the head to the dorsal fin origin in some species. The ventral profile is slightly convex at the abdomen but is straight posteriorly. The caudal peduncle depth is approximately equal to its length in most species, though the depth is less than the length in C. roae and greater in C. orientale. The eyes are placed on the sides of the head and are visible from above, but not from below. The mouth is subterminal and its width is anywhere between 40–60% of the head length. They have three pairs of barbels, one pair of maxillary barbels and two pairs of mental barbels; the medial mental barbels are slightly shorter than the lateral mental barbels, which are in turn slightly shorter than the slender maxillary barbels. The anal fin is moderately long, beginning about halfway down the body, with the posterior-most anal fin rays with a slight, membranous attachment to the body. The pelvic fins are usually small. The first pectoral fin ray is spinous and is slightly longer than one-half the length of the first branched ray; however, the spine may have a prolonged distal filament in mature males.
Sexual dimorphism
is observed in C. ferreirai, C. morenoi, C. orientale, and C. pemon, but not in C. minutum or C. roae. Presumed mature males have the first ray of the dorsal and pectoral fins extended into filaments except in C. ferreirai. Also, the anal fin has a broadly convex margin rather than a straight margin.
Cetopsidium species are smaller than Cetopsis species, growing to only 3.7–5.8 centimetres (1.5–2.3 in) SL
.
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...
Cetopsidae
Cetopsidae
Cetopsidae is a small family of catfishes , commonly called the whale catfishes.-Taxonomy:This family contains five genera. It is divided into two subfamilies, Cetopsinae and Helogeneinae. Helogeneinae was previously a family-level group, but now it has been reclassified as a subfamily of Cetopsidae...
. It includes seven species, C. ferreirai, C. minutum, C. morenoi, C. orientale, C. pemon, C. roae, and C. soniae.
Taxonomy
Cetopsidium was described in 2005, its name coming from the CetopsisCetopsis
Cetopsis is a genus of catfishes of the family Cetopsidae.-Taxonomy:Cetopsis is one of four genera in the subfamily Cetopsinae within the family Cetopsidae. Cetopsis is greatly expanded from when it only included C. coecutiens...
, the first described cetopsid genus, and idium which means dimunutive, in reference to the relatively small size of Cetopsidium species. Three existing species were transferred to this genus and three new species were described. In 2009 a new species, Cetopsidium soniae, was described bringing the number of species in the genus to seven.
Distribution
C. ferreirai is known only from the Trombetas River, a left bank tributary of the lower Amazon RiverAmazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
. C. minutum occurs in the Potaro River
Potaro River
The Potaro River is a river in Guyana in northern South America.The source of the Potaro River is in the Mount Ayanganna area of the Pakaraima Mountains in the North Rupununi Savannahs...
and middle portion of the Essequibo River
Essequibo River
The Esequibo River is the largest river in Guyana, and the largest river between the Orinoco and Amazon. Rising in the Acarai Mountains near the Brazil-Guyana border, the Essequibo flows to the north for 1,010 km through forest and savanna into the Atlantic Ocean.-Geography:There are countless...
of Guyana
Guyana
Guyana , officially the Co-operative Republic of Guyana, previously the colony of British Guiana, is a sovereign state on the northern coast of South America that is culturally part of the Anglophone Caribbean. Guyana was a former colony of the Dutch and of the British...
. C. morenoi is known from the central and western portions of the Orinoco
Orinoco
The Orinoco is one of the longest rivers in South America at . Its drainage basin, sometimes called the Orinoquia, covers , with 76.3% of it in Venezuela and the remainder in Colombia...
River basin in Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
and Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
. C. orientale is known from the coastal rivers of Suriname and French Guiana
French Guiana
French Guiana is an overseas region of France, consisting of a single overseas department located on the northern Atlantic coast of South America. It has borders with two nations, Brazil to the east and south, and Suriname to the west...
in the region from the Corantijn River along the border between Suriname and Guyana to the Oyapock
Oyapock River
The Oyapock or Oiapoque River is a 370-km long river in South America that forms most of the border between French Guiana and the Brazilian state of Amapá...
-Oiapoque River along the French Guiana-Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
border; it is likely this species is also occurs in the left bank tributaries to the Corantijn River draining from Guyana and the Oiapoque River in Brazil. C. pemon is known from the Caroni River
Caroní River
The Caroni River is the second most important river of Venezuela, the second in flow, and one of the longest, 952 km from the Tepui Kuquenan, where she originates with the same name Kuquenan, up to its confluence with the River Orinoco to which basin she belongs...
and the Caura River
Caura River
The Tacarigua River is a river on the island of Trinidad in the country of Trinidad and Tobago. It originates in the Northern Range and drains the Caura Valley. It passes through the town of Tacarigua in the East-West Corridor before joining the Caroni River. The Caura River is important both...
basins, southern tributaries of the Orinoco in eastern Venezuela, the Meta River
Meta River
The Meta River is formed in the Meta Department, Colombia by the confluence of the Humea, Guatiquía and Guayuriba rivers. It flows east-northeastward across the Llanos Orientales plains of Colombia through an ancient fault...
basin of the western portions of the Orinoco system in eastern Colombia, and the upper portions of the Branco River
Branco River
The Rio Branco is the principal affluent of the Rio Negro from the north; it is enriched by many streams from the sierras which separate Venezuela and Guyana from Brazil. Its two upper main tributaries are the Urariquira and the Takutu...
in northern Brazil. C. roae is only known from the Rupununi
Rupununi
Rupununi is a river and region in southern Guyana, South America, originating in the Kanuku Mountains. The Rupununi River runs from near the Brazilian border into the Essequibo River. The river during the flood season actually shares a watershed with the Amazon...
region of southwestern Guyana
Guyana
Guyana , officially the Co-operative Republic of Guyana, previously the colony of British Guiana, is a sovereign state on the northern coast of South America that is culturally part of the Anglophone Caribbean. Guyana was a former colony of the Dutch and of the British...
.
Description
The combination of the presence of a dorsal finDorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
with an ossified spinelet and the presence of pectoral-fin and dorsal-fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
spines distinguishes the species of Cetopsidium from all other genera in the Cetopsinae. A 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...
extending to over the posterior portion of the base of the anal fin but falling short of the caudal peduncle is also unique in this genus; the lateral line is usually longer than this, though it is shorter in two species of Denticetopsis
Denticetopsis
Denticetopsis is a genus of catfishes of the family Cetopsidae. It includes seven species, D. epa, D. iwokrama, D. macilenta, D. praecox, D. royeroi, D. sauli, and D. seducta.-Taxonomy:...
. Cetopsidium species have mental 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...
extending posteriorly beyond the rear margin of the opercle
Ichthyology terms
Ichthyology uses several terms that are unique to the science.Contents: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z- A :* Abdomen: belly* Abdominal: pertaining to the belly* Actinosts: a series of bones at the base of the pectoral rays....
and a deeply-forked, symmeterical caudal-fin margin with the tips of the lobes slightly blunt or rounded.
The body is elongate to moderately robust; anteriorly the body is not compressed much, but becomes progressively compressed posteriorly. The lateral line is incomplete, unbranched, and midlateral. In most species the dorsal profile is straight, though it may be slightly convex from the head to the dorsal fin origin in some species. The ventral profile is slightly convex at the abdomen but is straight posteriorly. The caudal peduncle depth is approximately equal to its length in most species, though the depth is less than the length in C. roae and greater in C. orientale. The eyes are placed on the sides of the head and are visible from above, but not from below. The mouth is subterminal and its width is anywhere between 40–60% of the head length. They have three pairs of barbels, one pair of maxillary barbels and two pairs of mental barbels; the medial mental barbels are slightly shorter than the lateral mental barbels, which are in turn slightly shorter than the slender maxillary barbels. The anal fin is moderately long, beginning about halfway down the body, with the posterior-most anal fin rays with a slight, membranous attachment to the body. The pelvic fins are usually small. The first pectoral fin ray is spinous and is slightly longer than one-half the length of the first branched ray; however, the spine may have a prolonged distal filament in mature males.
Sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
is observed in C. ferreirai, C. morenoi, C. orientale, and C. pemon, but not in C. minutum or C. roae. Presumed mature males have the first ray of the dorsal and pectoral fins extended into filaments except in C. ferreirai. Also, the anal fin has a broadly convex margin rather than a straight margin.
Cetopsidium species are smaller than Cetopsis species, growing to only 3.7–5.8 centimetres (1.5–2.3 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:...
.