| Cynodon gibbus | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Cynodontidae |
| Genus: | Cynodon |
| Species: | C. gibbus |
| Binomial name | |
| Cynodon gibbus | |
| Synonyms[3] | |
| |
Cynodon gibbus, known as thedogtooth characin,snub-nosed payara, andAgassiz's payara, is aspecies offreshwater fish in theCynodontidae family of the orderCharaciformes. It is apiscivore (fish eater) that occurs in rivers, lakes, and lagoons throughout much of northern South America, including theAmazon River basin. The species isfished bysubsistence fishermen,commercial fishermen, andsport fishermen. Mostly silver-gray with a spot behind thegill opening and another at thecaudal fin, it has long, sharp teeth and reaches a maximum of 32.2 centimetres (12.7 in) instandard length and 487.66 grams (1.08 lb). The species is abundant in its range. Firstdescribed byLouis Agassiz in 1829, it is one of three species in the genusCynodon, alongsideC. septenarius andC. meionactis.
Cynodon gibbus was firstdescribed byLouis Agassiz in 1829 under thebasionym (originalscientific name)Rhaphiodon gibbus.[3] It is classified in theCynodontidae family (the dogtooth characins) in the orderCharaciformes. It is also known by thecommon names dogtooth characin,[1] snub-nosed payara,[1] and Agassiz's payara.[4] In Spanish, it is known by the common nameschambira andperro, and its Portuguese common names includeaicanga,peixe-cachorro,peixe-ripa, andzé-do-ó.[1]
Thetype specimen is MZUSP 6539, aneotype (a replacement for a lost or damagedholotype) measuring 146.0 millimetres (5.75 in) instandard length collected fromLago Manacapuru inAmazonas, Brazil. The holotype (original type specimen) is lost; it may have been among a number of biological specimens housed at theZoologische Staatssammlung München in Germany and destroyed in 1944 duringa World War II bombing raid.[5]
This fish is the largest of the three species in the genusCynodon, all of which are found in South America.[6] The genus nameCynodon comes from the Greekkyon, meaning "dog", andodous, meaning "tooth", which refers to the longcanine-like teeth found in the members of the genus.[7][8] Thespecific namegibbus is the Latin word for "humped", referring to the shape of the fish's ventral, or belly, side.[8]
The genus name is attributed toJohann Baptist von Spix, who had been studying and collecting samples of the freshwater fish of Brazil until his death in 1826. Agassiz placedC. gibbus in the genusRhaphiodon instead of Spix's suggestionCynodon because the nameCynodon had already been used fora plant genus.Georges Cuvier also introduced the nameCynodon in 1829, but conflatedC. gibbus withHydrocyon scomberoides. A 2002 decision by theInternational Code of Zoological Nomenclature (ICZN) placedC. gibbus as thetype species ofCynodon andRhaphiodon vulpinus as the type species ofRhaphiodon, and additionally suppressed uses ofCynodon before that of Spix and Agassiz, including Cuvier's.[9][10]
C. gibbus occurs in theAmazon,Tocantins-Araguaia, andOrinoco river basins of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, and Venezuela. It is also found in Guyana's coastal river drainages. It is apelagic fish (living away from the shore and near the water surface) that prefers clear water in lakes, rivers, streams, and lagoons.[1] It is tolerant ofbrackish water.[7] The fish has an estimatedextent of occurrence of 8,144,567 km2 (3,144,635 mi2).[1] It ismigratory, traveling from 500 kilometres (310 mi) to 1,500 km (930 mi), though as itsreproduction has not been extensively studied, its spawning area remains unknown.[11]
This species grows up to 32.2 cm (12.7 in) instandard length and a weight of 487.66 g (1.08 lb).[7] It has a short, deep body with smooth,cycloid scales. It is silver-gray in color with a dark spot behind thegill opening, and a second spot at the base of thecaudal fin. Thedorsal fin is parallel to the beginning of theanal fin.[11] The long anal fin is characteristic of theCynodon genus (with at least 60 rays in all members of the genus), in comparison to the otherCynodontidae family members,Rhaphiodon andHydrolycus, which have fewer than 50.[5] Theadipose fin is transparent. Its mouth is facing upwards; in side view and when closed, it forms an angle greater than 80°. It has long, sharp,canine-like teeth.[11]
When differentiatingC. gibbus from the other members of its genus, it can be contrasted withCynodon septenarius by its eightpelvic fin rays, whereasC. septenarnius has seven; additionally,C. septenarius lacks a spot on the caudal fin. The orbital diameter is slightly smaller than that ofCynodon meionactis (average of 29.2% versus 31.8% of thehead length, and even larger inC. septenarnius), and whileG. gibbus rarely has fewer than 68 anal fin rays,C. meionactis never has more than 67.[5]
C. gibbus has 54 pairs ofchromosomes.[12] In contrast with many other animals such asmammals, where females have XXsex chromosomes and males have XY sex chromosomes,[13]C. gibbus is one of several fishes that is observed to follow theZW sex-determination system, in which males have ZZ sex chromosomes and females have ZW sex chromosomes. The W chromosome contains sequences of repeatedDNA, and while these sequences are believed to play a role in chromosomaldifferentiation, their precise function is unknown.[12]
Like other members of theCynodontidae family,larvae ofC. gibbus are elongate, with small eyes and a wide mouth containing conical teeth. The larvae are distinguishable from others of similar species by the shape of theswim bladder (oval in early stages, and triangular in later stages), the number of themyomeres (blocks of muscle) around the anus, and the presence of pigments around the rectum andcaudal peduncle (the part of the tail before the caudal fin begins). The position of the dorsal fin over the anal fin, as well as the pectoral fin's length stopping short of the beginning of the swim bladder, are further identifying characteristics.[11]
This species is a predator whose diet is primarily composed of other fish. It also occasionally feeds oninvertebrates. In its larval form, the fish consumeszooplankton, includingcladocerans andcopepods. The species does not exhibitparental care.[11]
The range ofC. gibbus and itscongener (other member of its genus)C. septenarius issympatric (overlapping). Both species are found alongside one another in theAmazon tributaryUatumã River. The two species are also found in theBranco River and theTrombetas River drainage, but have not been observed inhabiting the same localities. They do not occur withC. meionactis, which appearsendemic to theMaroni River ofFrench Guiana.[5]
C. gibbus is assessed as aleast concern species on theIUCN Red List. It is abundant in its range and has few identified threats.[1] The species is a target ofsubsistence fishing,commercial fishing, andsport fishing, and the fish's long, sharp teeth make their heads of interest toartisans.[11]
