Taxonomy & naming
Ancistrus jataiensis was formally described by Fisch-Muller, Cardoso, da Silva and Bertaco in 2005, alongside two other new Ancistrus species from the upper Tapajós and Tocantins drainages. The holotype — a male of 2 in standard length (MCP 35244) — was collected on 8 September 2002 from córrego Jataí, a small tributary of the rio Vermelho in the upper Tocantins basin, Goiás State, Brazil (14°29'S, 46°06'W). The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Ancistrus jataiensis, with no synonyms listed.
Within Loricariidae the species belongs to the tribe Ancistrini of subfamily Hypostominae. The genus Ancistrus — the bristlenoses — is one of the largest loricariid genera, with over 70 described species characterised by interopercular odontodes (the fleshy tentacles or bristles most visible on mature males) and by a generally flattened, heavily armoured profile suited to fast-flowing rocky substrates. A. jataiensis is distinguished from all known congeners by the complete absence of an adipose fin, which is replaced by a series of small unpaired platelets forming a low crest along the dorsal midline — an arrangement not recorded in any other Ancistrus at the time of description.
Morphology
The largest documented specimen reaches 2 in standard length (SL), placing A. jataiensis among the smaller members of its genus. The body follows the typical Ancistrus template: strongly depressed, broad head, ventrally positioned sucking disc, and a carapace of interlocking bony scutes that leave only the soft ventral surface unarmoured.
The defining morphological feature is the absence of an adipose fin. In the great majority of loricariids — including essentially all other Ancistrus — the adipose fin is a prominent fleshy lobe situated between the dorsal fin and the upper caudal lobe. In A. jataiensis this structure is replaced by a row of small, unpaired platelets forming a low bony crest; this character alone is sufficient to identify the species within its genus.
Additional diagnostic proportions, measured from the type series, include a relatively long predorsal length (47.5–49.3% SL) and a deeper occipital region (17.0–19.5% SL) compared to its closest relative A. reisi, and a shorter caudal peduncle (24.6–27.1% SL vs. 27.7–30.9% SL in A. reisi).
Sexual dimorphism follows the genus norm: larger males bear the characteristic branched snout tentacles (interopercular odontodes), which are absent or rudimentary in females and juveniles.
Habitat
Ancistrus jataiensis is known only from córrego Jataí, a small headwater stream draining into the rio Vermelho, itself a tributary of the upper Tocantins system in Goiás, Brazil. The collection site sits within the Cerrado biome — South America's vast tropical savannah, characterised by seasonal rainfall, lateritic soils, and gallery forests lining watercourses through open grassland.
Cerrado streams typically run clear to lightly tea-coloured over rocky or sandy substrates, with water temperatures that fluctuate markedly between wet and dry seasons. Headwater streams in this region are often shallow and swift during rains, becoming reduced, warmer, and more concentrated in dissolved minerals during the dry season. Specific water-chemistry measurements from the type locality are not available in the literature, but Cerrado gallery-stream fish generally encounter warm (72–82 °F), soft to moderately hard, mildly acidic to neutral water.
The extremely restricted range — a single small stream — makes A. jataiensis a true microendemic, an isolation likely produced by the fragmented hydrology of the upper Tocantins headwaters.
Feeding
No feeding data specific to Ancistrus jataiensis have been published. By analogy with the wider genus, it is almost certainly a periphyton scraper and biofilm grazer: the loricariid sucking disc and fine, multi-cusped teeth are well adapted to rasping algae, diatoms, and microbial mats from submerged rocks and woody debris. Organic fine particulates and the occasional invertebrate swept past in current likely supplement the diet, as is typical in Cerrado stream fishes of this guild.
In any captive context, standard Ancistrus husbandry foods — algae wafers, spirulina discs, and blanched vegetables such as courgette and cucumber — would be appropriate, alongside a stable supply of algae-covered surfaces or smooth rock for natural foraging behaviour.
Mating
Mating behaviour in A. jataiensis has not been documented in the wild or in captivity. General Ancistrus biology provides a reasonable template: males are territorial around rocky crevices and potential spawning sites, advertising fitness through the elaborate branched tentacles that distinguish mature individuals. Rival males display and may engage in physical contests mediated by their interopercular odontodes, while receptive females are coaxed into the chosen cavity.
Given the species' small adult size (under 2.5 in SL), spawning sites are likely correspondingly compact — tight rock crevices or spaces beneath boulders in the swift headwater streambed.
Breeding
No breeding accounts for Ancistrus jataiensis exist in the published literature or the hobbyist record, which is unsurprising given that the species has not been reported in the ornamental trade. The general Ancistrus breeding pattern — cave spawning with adhesive eggs and paternal brood care, the male fanning the clutch until fry emerge and disperse — would be expected here, but specifics of clutch size, incubation duration, and fry development remain undocumented.
In the aquarium
Ancistrus jataiensis has not been reported in the aquarium trade and is unlikely to be available to hobbyists. Its microendemic status — confined to a single stream — and the absence of commercial collection from its remote Cerrado habitat mean it is effectively unknown outside a small number of ichthyological collections.
Were specimens to become available, care would logically mirror that of other small Ancistrus from oxygen-rich, seasonally variable headwaters: a well-aerated tank with smooth river cobbles, moderate current, clean water, and a diet of algae-based foods and blanched vegetables. Water chemistry in the Cerrado headwater range (soft to moderately hard, pH 6.5–7.5, temperature 72–81 °F) would be a reasonable target. The distinctive absence of an adipose fin would be the immediate visual clue distinguishing this species from the many superficially similar bristlenoses in the trade.
Conservation
The IUCN Red List assessed Ancistrus jataiensis as Data Deficient (DD) in 2018, reflecting the very limited information available on population size, trends, and threats. The species is known from a single small stream within the Cerrado biome, one of the world's most threatened biodiversity hotspots. Approximately 50% of the original Cerrado has been converted to agriculture — principally soya and cattle ranching — and riparian gallery forests in Goiás State face continued clearing, increased sedimentation, and altered seasonal hydrology.
For a species with so restricted a range, any sustained degradation of córrego Jataí or its immediate catchment could constitute a severe threat. No targeted conservation measures are recorded. Its classification should be revisited with dedicated field surveys to establish population size and habitat condition.