Ancistrus

With 59 currently accepted species, Ancistrus is the largest genus of Ancistrini. It is readily recognized from all other loricariids by the presence of tentacles on the snout. In females and juveniles, the tentacles are short and located only along the snout margin; however, in breeding males, the tentacles are quite long and located on the top of the snout. Based on the fact that males guard their young until they are fairly large and that females of nest-building species prefer to lay eggs in the nest of males that already have eggs, Sabaj et al. (1999) suggest that female Ancistrus, given the choice, will prefer to lay eggs in nests of males that are already guarding young because that male has shown himself to be a fit parent. If such is true, it is likely that the tentacles have evolved as larval mimics to trick the female into laying eggs in the nest. Indeed, the tentacles are the size and coloration of juvenile Ancistrus ready to leave the nest. The following is an excerpt from Armbruster (1997).

GENUS SYNONYMY

Ancistrus is diagnosed by one unique characteristic: long, fleshy tentacles on the snout without basal odontodes. Other characteristics considered synapomorphic for Ancistrus are: constriction of the hypohyal anteriorly and posteriorly, a shortened anterior process of the metapterygoid, extension of the mesethmoid disk beyond the anterior margin of the main body of the metapterygoid, an enlarged, almost square, nasal, loss of the parasphenoid shelf, a widened ventral section of the sphenotic, reduction in the number of branched anal fin rays to four, and a naked snout margin.

Species of Ancistrus are small- to medium-sized loricariids that are easily recognizable by the presence of large, fleshy tentacles on the snouts of breeding males (smaller tentacles are present on the snouts of females and juveniles). Color pattern typically dark gray to black, often with white or gold spots. Abdomen naked. Caudal fin straight, angled posteroventrally, to slightly emarginate with the lower lobe longer. Snout is naked along the edge in females and juveniles and, maximally, to the nares in adult males. Usually four predorsal plates. Three rows of plates on the caudal peduncle. The nuchal plate may be exposed or covered in plates.

Males possess large, fleshy tentacles on the snout and pectoral fin spines. The cheek odontodes of males are larger and more numerous than those of females. Males have elongated odontodes on the leading edges of the pectoral fin spines.

Ancistrus can be distinguished from all loricariids except some Chaetostoma and breeding male Pareiorhaphis by a lack of plates along the snout margin. Ancistrus differs from all the above by having tentacles on the snout and from the Pareiorhaphis by having evertible cheek odontodes and no odontodes along the snout (the odontodes are not evertible in Pareiorhaphis and they proceed onto the snout margin). Among the Ancistrini, Ancistrus is most similar to Lasiancistrus which has plates on the snout margin and long, thin, whiskerlike odontodes in the cheek mass and on the opercle. Lasiancistrus also develops tentacules along the snout of breeding males; however, these tentacules are always associated with odontodes while no odontodes are present along the snout of Ancistrus.

Ancistrus is found in a wide variety of habitats from fast-flowing rivers to floodplain lakes. Ancistrus has been shown to breathe air in hypoxic conditions (Gee, 1976). Males defend nests in cavities where females lay large clumps of eggs. Males defend young after hatching and until they have pigment and have absorbed their yolk sacs (Burgess, 1989, pers. obs.). Several clutches in various states of development from eggs to free-swimming larvae can be found in one nest (Sabaj et al., 1999). Sabaj et al. (1999) suggest that the tentacles may act as larval mimics and exploit a pre-existing bias in females for the presence of larvae in the nest.

Ancistrus is one of the widest-ranging loricariids and occurs almost throughout the range of Loricariidae.

Armbruster, J.W. 1997. Phylogenetic relationships of the sucker-mouth armored catfishes (Loricariidae) with particular emphasis on the Ancistrinae, Hypostominae, and Neoplecostominae. Unpubl. Ph.D. dissertation. University of Illinois, Urbana-Champaign. 409 pp.

Burgess, W.E., 1989. An atlas of freshwater and marine catfishes, a preliminary survey of the Siluriformes. T.F.H. Publications, Neptune City, New Jersey. 784 pp.

Gee, J.H. 1976. Buoyancy and aerial respiration: factors influencing the evolution of reduced swim-bladder volume of some Central American catfishes (Trichomycteridae, Callichthyidae, Loricariidae, Astroblepidae). Can. J. Zool. 54:1030?1037.

Sabaj, M.H., J.W. Armbruster, and L.M. Page. 1999. Spawning in Ancistrus with comments on the evolution of snout tentacles as a novel reproductive strategy: larval mimicry. Ichthyological Exploration of Freshwaters 10:217-229.

Val, A.L. and V.M.F. de Almeida-Val. 1995. Fishes of the Amazon and their environment. Zoophysiology Vol. 32. Springer-Verlag, Berlin. 224 pp.