Taxonomy & naming
Ancistomus feldbergae was formally described by de Oliveira, Rapp Py-Daniel, Zuanon, and Rocha in 2012 in Copeia (volume 2012, number 3, pp. 547, Figs. 1–3). The original combination was Peckoltia feldbergae; FishBase retains the old URL path under Peckoltia, but the Catalog of Fishes (Eschmeyer, CAS) and PlanetCatfish both recognise the current valid combination as Ancistomus feldbergae. The reassignment from Peckoltia to Ancistomus reflected morphological diagnoses that placed this species, and others sharing its key characters, outside the Peckoltia sensu stricto group.
The genus Ancistomus is distinguished from Peckoltia by a suite of characters including dark thin longitudinal stripes in the interradial membranes of the dorsal fin (parallel to the fin rays, fragmenting into dots in larger adults), an orange or reddish band on the distal margin of the caudal and dorsal fins, and dark brown spots covering the entire body. Additional characters given in the original description include a postanal length of 28.4–32.4% SL and head depth of 48.2–60.4% HL.
In the aquarium hobby the species circulates under two L-numbers — L012 and L013 — both of which were assigned before the formal description, as was common practice for Xingu plecos entering the trade before scientists had described them. L012 is the primary code; L013 also refers to this taxon and appears in some hobby sources. Both codes are retained in the common-names list for searchability.
Morphology
Ancistomus feldbergae reaches approximately 6.5 in standard length (SL) based on FishBase (Ref. 91751, the original description data). PlanetCatfish records up to 8 in SL for captive specimens, suggesting potential for somewhat larger growth in aquarium conditions, though figures from the type series are considered the baseline for the species.
The dorsal fin formula is D I,7 with 5 anal-fin rays. Ground coloration is dark brown, covered in dark brown to black spots across the entire body and fins. The key diagnostic features of the genus are present: fine longitudinal stripes in the dorsal-fin interradial membranes, which run parallel to the fin rays in juveniles and begin to fragment into dots as the fish grows. The distal margins of the caudal and dorsal fins carry an orange to reddish band — a striking accent that aids identification and makes this one of the more visually distinctive mid-sized Xingu loricariids.
Sexual dimorphism is not documented in the original description from the material examined. As a hypostominae member, modest odontode development on the pectoral spines and interopercular region would be expected in males, but specific information for this species is lacking.
Habitat
The type locality is the Rio Xingu at Ilha de Babaquara, upstream of Altamira, Pará, Brazil (3°23'45"S, 52°12'16"W). The Rio Xingu is one of the major southern tributaries of the lower Amazon, famous among loricariid researchers and hobbyists for its extraordinary diversity of armoured catfishes. The stretch upstream of Altamira — the Volta Grande do Xingu — comprises fast-flowing, oxygen-rich rapids over a rocky substrate of flat plates and boulders.
Field observations documented in the original description (FishBase Ref. 91751) note that A. feldbergae occurs in shallow rapids over small to medium flat rocks (up to approximately 19.5 in diameter), coarse sand, and pebbles. The fish hides under rocks during daylight hours and forages on the epilithon — the community of diatoms, algae, and associated microorganisms coating the rock surfaces — at night.
Water temperatures in the Xingu rapids vary seasonally but are generally warm, and PlanetCatfish records 77–86 °F (77–86 °F) as the range for this species. No pH data specific to A. feldbergae's microhabitat are recorded in the available sources.
This portion of the Xingu is the area most directly threatened by the Belo Monte hydroelectric complex, a consideration of significant conservation relevance (see Conservation section).
Feeding
Ancistomus feldbergae is principally an epilithic diatom grazer — one of the more precisely documented diets among Xingu loricariids. Stomach-content analysis from specimens in the original study (FishBase Ref. 91751) found that diatoms made up 83 percent of total stomach volume, with sponge fragments, sponge spicules, and sediment making up the remainder. This result is corroborated by gut anatomy: intestine length in this species is approximately 11 times the standard length, a ratio consistent with a high-fibre, low-nutrient food source requiring extended processing.
In the aquarium, the diet should reflect this biofilm specialisation. Surfaces colonised by algae and diatom films — mature, established rocks, driftwood, and tank glass — are the primary food source. Supplementary foods should be vegetable-based: algae wafers, spirulina tablets, blanched courgette, cucumber, and similar material. The species is listed as a commercial aquarium and fisheries species on FishBase, indicating it has been kept in captivity, though detailed keeper reports are limited.
Mating
Specific courtship observations for Ancistomus feldbergae in captivity are not on record in the available sources. PlanetCatfish records no captive breeding reports as of the time this cache was compiled. The general pattern for Hypostominae — territorial males defending spawning sites, with odontode display as a component of male competition — can be inferred but not stated as observed for this species.
Data sparse: Xingu rapids species of this type are often challenging to condition in captivity due to their specialist habitat requirements, and detailed mating observations are uncommon.
Breeding
No captive breeding of Ancistomus feldbergae has been documented in the standard hobby references. PlanetCatfish records no breeding reports. Given the species' rapids habitat and diatom-specialist diet, replicating the precise conditions — fast, highly oxygenated, warm water with abundant biofilm on flat rock surfaces — that would be needed to bring this fish into breeding condition is demanding.
Breeding mode is presumed to be typical Hypostominae cave-spawning with some form of parental guarding, but this cannot be stated as established fact for this species.
Data sparse.
In the aquarium
Ancistomus feldbergae enters the trade as L012 (and occasionally L013) and is periodically available through specialist loricariid importers. It is not a common aquarium fish, and most specimens in the hobby originate from the Xingu trade rather than captive breeding.
Keeping this species well requires attention to its natural habitat: strong water movement is essential, and filtration should create a vigorous current across a rock-heavy substrate. The temperature range of 77–86 °F should be maintained consistently. Regular, generous water changes are important, both to maintain oxygen levels and to approximate the constantly replenished water of fast-flowing rapids.
Established biological films on tank surfaces, mature rock, and driftwood provide a significant proportion of the diet. Supplementary algae wafers, spirulina foods, and blanched vegetables should be offered. Driftwood is beneficial for enrichment and hiding, though this species is not a xylophage and wood is not a dietary necessity.
At up to 6.5 in SL, adults need a reasonably large tank — 40 US gal or more is advisable, with a long footprint that allows adequate water flow. The species is not documented as aggressive, but Xingu loricariids generally show some territorial behaviour around preferred resting sites. Tankmates should be species tolerant of strong current; delicate slow-water fish are not appropriate companions.
Conservation
Ancistomus feldbergae is assessed as Least Concern on the IUCN Red List (assessed 7 November 2018). At the time of assessment, the species was considered to have a sufficient distribution within the Xingu drainage and no immediate threats qualifying it for a threatened category.
However, the Xingu drainage — and specifically the Volta Grande do Xingu upstream of Altamira where this species' type locality falls — is the region most severely affected by the Belo Monte hydroelectric dam complex, which began operation in the 2010s and has fundamentally altered river flow, temperature, and sediment dynamics in the area. The rapids habitat that A. feldbergae depends on is precisely the habitat type most vulnerable to flow reduction downstream of a large dam. A reassessment that more fully accounts for post-Belo-Monte conditions may warrant a different conclusion.
The species is listed as a fisheries and commercial aquarium species on FishBase, indicating collection pressure in addition to habitat modification. Captive breeding is not established, meaning the trade is currently dependent on wild-caught fish from an already-impacted drainage.