Retroculus Eigenmann & Bray

Synonymy

Retroculus Eigenmann & Bray, 1894. Ann. N.Y. Acad. Sci., 7, p. 614 (type by monotypy Retroculus boulengeri Eigenmann & Bray). Gender masculine.

Retroculus lapidifer. Freshly caught specimen from the Rio das Mortes, Brazil. Photo: U. Werner.

Diagnosis

South American cichlids with numerous plesiomorphic characters such as five dentary lateralis pores, seven preopercular lateralis pores, African type lips, numerous epibranchial gill rakers. No autapomorphies recorded in literature, but with numerous characters indicative of rheophily, especially wide, short pelvic fin with middle ray longest, and minute ventral scales. Superficially similar to Geophagus but without anteroventral expansion on the first epibranchial. Retroculus has usually been associated with geophagine cichlids, but Kullander (1998) suggested that Retroculus holds a basal position among Neotropical cichlids. Retroculus lapidifer and R. septentrionalis grow to about 20 cm SL, R. xinguensis reaches at least 140 mm SL.

See Gosse (1971) for recent revision with excellent drawings of all species included.

Included species

Retroculus lapidifer (Castelnau, 1855)

Retroculus boulengeri Eigenmann & Bray, 1894.

Retroculus septentrionalis Gosse, 1971

Retroculus xinguensis Gosse, 1971

Identification guide

Retroculus lapidifer: Dorsal fin XV-XVII.10-11, A. III.6-7. Scales in a lateral row 36-39. Gill rakers 10-13. Caudal fin without vertical stripes
Retroculus xinguensis: Dorsal fin XVI-XVII.10-12. A. III.6-7. Scales in a lateral row 37-41. Gill rakers 10-12. Caudal fin with distinct vertical stripes.
Retroculus septentrionalis: Dorsal fin XIV-XV.10-11. A. III.6-7. Scales in a lateral row 34-37. Gill rakers 13-15. Caudal fin with distinct vertical stripes.

Etymology

Retroculus, from retro, Latin adverb (re and ter), referring to position backwards, back, on the back side, behind; and oculus, Latin noun meaning eye. The name refers to the relatively posterior position of the eye in the head as compared to other cichlids.

Geographical distribution

Retroculus lapidifer is collected in the Tocantins and Capim drainages; R. xinguensis in the Xingu and Arapiuns drainages; and R. septentrionalis in the Oyapock and Araguari drainages.

Natural history

Retroculus species are restricted to rapids or running water in a few clear water rivers on the Guiana and Brazilian shielfs. Retroculus lapidifer and R. xinguensis are bottom feeders, with chironomid, trichoptera and ephemeroptera larvae dominating the diet (Moreira & Zuanon, 2002), and R. septentrionalis may be expected to have similar feeding habits. The reproductive behaviour is incompletely known. Already Castelnau (1855) observed R. lapidifer carrying pebbles in the mouth. Recent aquarium (Weidner, 1999; Lucas, 1999) and field observations confirm that at least R. lapidifer excavates bottom substrate to a pit in which eggs are deposited and then covered with sand or pebbles. Both parents guard the nest, but aquarium observations so far could not be extended beyond the first day, after which the eggs disappeared, probably eaten by the parents.

Local names

Not recorded.

References

CASTELNAU, F. de. 1855. Animaux nouveaux ou rares recueillis pendant l'expédition dans les parties centrales de l'Amérique du sud, de Rio de Janeiro a Lima, et de Lima au Para; exécutée par ordre du gouvernement francais pendant les années 1843 a 1847, sous la direction du Comte Francis de Castelnau. Poissons. Paris.
GOSSE, J.P. 1971. Révision du genre Retroculus (Castelnau, 1855), designation d'un neotype de Retroculus lapidifer (Castelnau, 1855) et description de deux espèces nouvelles. Bulletin, Institut royale des Sicences naturelles de Belgique, 47 (43): 1-13.
KULLANDER, S.O. 1998. A phylogeny and classification of the South American Cichlidae (Teleostei: Perciformes). Pp. 461-498 in Malabarba, L.R, R.E. Reis, R.P. Vari, Z.M.S. Lucena, & C.A.S. Lucena (eds), Phylogeny and Classification of Neotropical Fishes. Edipucrs, Porto Alegre.
LUCAS, P. 1999. Retroculus sp. Eine kleine Buntbarsch-Sensation aus Südamerika. Das Aquarium, (363): 8-14.
MOREIRA, S.S. & J. ZUANON, 2002. Dieta de Retroculus lapidifer (Perciformes: Cichlidae), peixe reofílico do rio Araguaia, Estado do Tocantins, Brasil. Acta Amazonica, 32: 691-705
WEIDNER, T. 1999. Retroculus lapidifer - Steinträger und Grubenlaicher. DATZ, 52 (9): 8-12.