Taxonomy & naming
Ancistrus greeni was described by Isbrücker in 2001 in the DATZ-Sonderheft Harnischwelse 2 (Special Issue on Armoured Catfishes No. 2), a dedicated German-language harnischwelse publication, on page 24. The Catalog of Fishes (Eschmeyer, CAS) records the valid combination as Ancistrus greeni (Isbrücker, 2001); the parenthetical authority indicates that the species was originally described under a different generic combination before being placed in Ancistrus.
Several synonyms are associated with this species: Chaetostoma greeni, Chaetostomus aculeatus maculatus, and Chaetostomus maculatus — all reflecting earlier generic placements that predate the current Ancistrus assignment formalised by Isbrücker. The species sits within the tribe Ancistrini of subfamily Hypostominae (Armbruster, 2004), the dominant lineage of armoured catfishes in Amazonian and Andean drainages.
The species epithet honours M.J. Green, an artist; no further biographical detail for this individual has been located in accessible sources. A multilocus molecular phylogenetic study of the Chaetostoma clade (Hypostominae) by Lujan, Armbruster, Lovejoy, and López-Fernández, published in Copeia in 2015 (vol. 103, no. 3, pp. 664–701), provides the most recent phylogenetic context for species in this group. No L-number designation has been applied to A. greeni.
Morphology
Ancistrus greeni is a small species, reaching approximately 2.5 in standard length (SL) based on measurements from PlanetCatfish; FishBase records the same figure as total length (TL), and the SL value from PlanetCatfish is treated as the more precise measurement. Adults are therefore compact, consistent with the generally small body size found across much of the genus.
The defining characteristic of Ancistrus males is the development of soft, fleshy tentacles — unbranched or branched filaments — on the snout and along the leading edge of the head. These tentacles, absent or greatly reduced in females and juveniles, are the most reliable external marker for the genus and distinguish Ancistrus from the largely tentacle-free Hypostomus. Male A. greeni develop extensive snout tentacles at maturity; females possess few and smaller tentacles or none.
Beyond body size and tentacle development, detailed morphological data specific to A. greeni — meristic counts, colour pattern description, and scute arrangement — are not available in sources accessible for this article. The original 2001 description in a specialist grey-literature journal has not been widely reproduced in the ichthyological literature.
Habitat
Ancistrus greeni is recorded from the Amazon basin in Peru, with a distribution spanning the Middle Amazon (Solimões), Madeira, Madre de Dios, and Inambari drainages according to PlanetCatfish records. The type locality is listed as 'Rozmaiu, Upper Peru' — a locality name that cannot be precisely geolocated; 'Upper Peru' is a broad historical designation for Amazonian Peru, and 'Rozmaiu' does not correspond to a currently identifiable place name in available geographical sources. The locality is therefore uncertain.
The river systems within the cited distribution encompass both Andean-foothill clearwater and whitewater rivers and lowland Amazonian tributaries. Specific water chemistry data for collection sites of A. greeni are not recorded in accessible sources. In Amazonian Peru broadly, rivers range from acidic, ion-poor blackwater (pH 4.5–6.0) to moderately alkaline whitewater (pH 6.5–7.5 at low water) with varying hardness and temperatures typically between 24 and 82 °F. Without site-specific data, water chemistry requirements for this species cannot be stated with confidence.
Feeding
No gut-content analysis or direct dietary data for Ancistrus greeni have been located. Diet is inferred from genus biology. Ancistrus species are primarily algae grazers and biofilm scrapers, using the ventral, disc-shaped mouth to rasp algae and organic detritus from hard surfaces — rocks, submerged wood, roots, and clay banks. Many species also opportunistically consume small invertebrates and plant matter.
In the aquarium context, Ancistrus species accept algae wafers, spirulina-based sinking foods, blanched courgette (zucchini), cucumber, and other vegetable matter. Small amounts of protein (frozen or live bloodworm, for instance) are tolerated but should not constitute the bulk of the diet. These generalisations apply across the genus and are not specific to A. greeni, for which no published dietary data exist.
Mating
Mating behaviour in Ancistrus greeni is undocumented. Across the genus Ancistrus, males are typically territorial and centre their activity on defended cavities — hollow logs, crevices, ceramic caves — which serve both as refuge and as spawning sites. The prominent snout tentacles of mature males are thought to play a role in intrasexual signalling or species recognition, though the precise function has not been experimentally confirmed for most species.
Males with more extensive tentacle development tend to be more reproductively mature. Rival male encounters in Ancistrus usually involve mutual display and occasional short physical contact; serious injury is uncommon where adequate territory is available. These details are derived from the genus-level literature and should not be read as specific observations of A. greeni.
Breeding
No breeding reports for Ancistrus greeni exist in the accessible literature or in hobbyist databases. PlanetCatfish records no breeding accounts and no hobbyist sightings for this species.
Across the genus, Ancistrus is a well-established cave spawner with paternal brood care: the male occupies and defends a cavity, courts the female into the site, and after spawning remains with the egg mass, fanning and cleaning the clutch until the fry are free-swimming. This pattern is documented in multiple Ancistrus species and underlies the genus's popularity as a manageable breeding project in the hobby. Whether A. greeni follows this pattern precisely cannot be confirmed without direct observation.
In the aquarium
Ancistrus greeni has no documented presence in the aquarium trade. No hobbyist sightings, import records, or care accounts have been located. The species therefore has no established aquarium profile.
For context: its small adult size (approximately 2.5 in SL) would in principle make it suitable for moderately sized aquaria, consistent with the broad range of small Ancistrus species that are successfully maintained in the hobby. Given the Amazonian Peruvian distribution, soft to moderately hard water with a pH in the range of 6.0–7.5 and temperatures of 75–81 °F would be a reasonable starting assumption, but these parameters are inferred from regional biogeography rather than documented collection-site data.
Any aquarium information beyond these general inferences would be speculative, and none is offered here. Should the species appear in trade in the future, care protocols appropriate to small, Amazonian Ancistrus would serve as a baseline.
Conservation
The IUCN Red List lists Ancistrus greeni as Data Deficient (DD), assessed in 2014. The DD designation indicates that insufficient information is available to make an assessment of extinction risk — not that the species is known to be secure, but that the data to evaluate its status do not exist. The combination of an uncertain type locality, a broad but poorly surveyed distributional range across Amazonian Peru, and no hobbyist or trade records means that population trends, abundance, and habitat associations are unknown.
The Amazonian drainages of Peru face ongoing pressure from deforestation, hydroelectric development, agricultural expansion, and artisanal gold mining, all of which alter riverine habitats for benthic species. Whether A. greeni is genuinely rare, locally common but overlooked, or distributed patchily across a wide range is not known. A taxonomic and distributional review, combined with field surveys in the Madre de Dios and Inambari basins, would be necessary to move this species out of the DD category.