HIGHER TAXON

Chaetobranchus is a genus of the subfamily Astronotinae, tribe Chaetobranchini, sister group of the tribe Astronotini. The most similar genus is Chaetobranchopsis

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AUTHOR

Sven O Kullander

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Chaetobranchus Heckel

Synonymy

Chaetobranchus Heckel, 1840. Annln wien. Mus. Natges. 2, p. 401 (type by subsequent designation by Eigenmann (1910, p. 469) Chaetobranchus flavescens Heckel). - Masculine.

Chaetobranchus semifasciatus. Photo © A. Kullander
Chaetobranchus semifasciatus. Photo: Anita Kullander.

Diagnosis

This genus is recognized for large (to ca 250 mm SL) South American cichlids distinguished in particular by specializations apparently associated with planktivory: gill rakers externally on first gill arch long, slender, close set (gradual size decrease towards skull and hypobranchial), 20-35 on epibranchial, ca 50-90 on cerato- and hypo-branchial, other rakers shorter and more spaced, but still relatively long and numerous. The mouth is large; jaw teeth are small, simple, pointed, in narrow bands in both jaws, running along entire upper jaw rim in adults. On the roof of the branchial chamber there is a narrow skin ridge above each first ceratobranchial. The lower pharyngeal tooth plate is long and slender, with deeply incised hind margin, and covered by numerous small pointed teeth. Both lip folds are continuous; the lower lip attaches to the hind edge of the upper lip fold well above distal tips of premaxilla and maxilla ('American type lips').

There are no gill rakers on the lower pharyngeal tooth plate, but there is a series of rudimentary microbranchiospines along the lateral edges. Microbranchiospines present also externally on the 2nd-4th arches and internally on the 4th, plate like, with rounded top and truncate bottom, and with many small teeth on exposed surface and some along lateral margins ventrally. Basibranchial 3 is usually toothed. Ceratobranchial 4 is edentulous.

The lateralis system includes 7 preopercular and 5 dentary lateralis canal openings; suborbital series consisting of lacrimal, 4 tube like infraorbitals (2nd with middle foramen); and several series of tubed scales on caudal fin: one long between rays D1-D2; on lower lobe either a few scales continuing lower lateral line plus long sequence between rays V2-3 or V3-4, or 2-3 long sequences between rays V1-2, V2-3 (variably present) and V3-4 respectively.

The predorsal squamation is irregular; anteroventrally on the cheek is a group of scales narrowly separate from the rest of the cheek squamation.

The positions of the caudal fin lateral lines is unusual among cichlids. Basibranchial tooth plates are not known from any other cichlids. They need more study with regard to possible homology with those of other percoids (e.g. in Greenwood 1976). A feature of uncertain interpretation is the shape of the microbranchiospines, shared with Astronotus and Chaetobranchopsis. The presence of microbranchiospines on the lower pharyngeal tooth plate is a feature unique to Chaetobranchus.

Only two species: Chaetobranchus flavescens Heckel (widely distributed in the Amazon basin, Guianas, and Orinoco basin) and C. semifasciatus Steindachner (central Amazon basin). They differ considerably, e.g., in colouration and squamation. Chaetobranchus semifasciatus has vertical bars and an ocellated spot on the caudal fin base, smaller scales (e.g. 20 instead of 16 circumpeduncular scale series) and narrowly scaled instead of naked vertical fins.

Chaetobranchopsis Steindachner is similar to Chaetobranchus but has extensively scaled vertical fins, 5-6 (occasionally 4) instead of 3 anal fin spines, and lacks basibranchial tooth plate.

Included species

Chaetobranchus flavescens Heckel, 1840
Chaetobranchus flavescens Heckel, 1840. Annln wien. Mus. Natges. 2, p. 402 (Fluss Guaporè und die in der Nähe seiner Ufer gelegenen Moräste, auch am Ausflusse des Rio-negro).
Chaetobranchus bruneus Heckel, 1840. Annln wien. Mus. Natges. 2, p. 405 (Rio-negro, unweit von seiner Mündung).
Centrarchus? cyanopterus Jardine, 1843. Nat. Libr. Ichthyol. 5, p. 165, Pl. 16 (Essequibo).
Chaetobranchus robustus Günther, 1862. Catal. Fish. Br. Mus. 4, p. 310 (Guiana).
Chromys ucayalensis Castelnau, 1855. Anim. nouv. rares. Poissons, p. 15, Pl. 6, fig. 2 (Sarayacu (Pérou)).
Geophagus badiipinnis Cope, 1872. Proc. Acad. nat. Sci. Philad. 23, p. 251, Pl. XI, fig. 1 (Ambyiacu River).
Chaetobranchus semifasciatus Steindachner, 1875
Chaetobranchus (Chaetobranchus) semifasciatus Steindachner, 1875. Sber. k. Akad. Wiss. Wien Math.-natw. Cl. 71, p. 130, Pl. VII (Amazonenstrom bei Obidos, Cudajas, Teffé; Rio Iça; Lago Hyanuary und Saraca bei Silva).

Key to species

Dorsal and anal fins naked; 16 circumpeduncular scale rows; no ocellated spot at caudal fin base; no vertical bars.................C. flavescens
Dorsal and anal fins scaled; 20 circumpeduncular scale rows; ocellated spot at caudal fin base; wide vertical bars on sides .....C. semifasciatus

Etymology

Chaetobranchus in allusion to the long gillrakers, from the Greek chaetos, thread, and branchia, gill.

Geographical distribution

Whereas C. semifasciatus appears limited to the Central Amazon, between about Óbidos and Tefé, C. flavescens is widely distributed in lowland Amazonia, the Guianas and the Orinoco drainage.

References

KULLANDER, S.O. 1986. Cichlid fishes of the Amazon River drainage of Peru. Stockholm, 431 pp.
KULLANDER, S.O. & H. NIJSSEN.1989. The cichlids of Surinam. E.J. Brill, Leiden and other cities, XXXIII+256 pp.