Taxonomy & naming
Apistogramma caudomaculata was described by Luz Marina Mesa Salazar and Carlos A. Lasso in 2011, in the third installment of their revision of the genus Apistogramma (Regan, 1913) in the Orinoco basin, published through the Humboldt Institute in Biota Colombiana. It was one of several new Orinoco species named in that work, alongside Apistogramma pedunculata, Apistogramma megaptera, and Apistogramma lineata among others.
Eschmeyer's Catalog of Fishes records the type locality as 'Maripa, río Caura, morichal Pozo Vagabundo, Estado Bolívar, Venezuela.' The holotype is held at the Museo de Historia Natural La Salle, Caracas (MHNLS 13413), with three paratypes (MHNLS 10986, 13922, 13934). The hobby authority Mike Wise has noted that the species probably corresponds to the fish illustrated by Staeck (1991) as an undescribed species from the río Caura, so it may have been on record informally well before it was named. No synonyms are in use, and the species is recognized as valid by the Catalog of Fishes and FishBase.
Morphology
This is a small dwarf cichlid, and the only published measurements are those of the type series in the 2011 revision: the holotype and paratypes span roughly 1–1.5 in in standard length — about 1–1.5 in from snout to tail base — placing it among the smaller Orinoco Apistogramma. FishBase carries no maximum-length entry, so those description figures are the sole reference.
The single feature that defines the species, and gives it its name, is the caudal blotch: a dark spot at the base of the tail fin, enlarged transversely so that it stands taller than it is long, more conspicuous and differently shaped than the caudal markings of its Orinoco relatives. Detailed coloration, fin-ray counts, and live-pattern descriptions stay confined to the 2011 revision and have not been widely reproduced. Mesa Salazar and Lasso describe the sexual dimorphism as present but not strongly marked — males run a little larger, with a more elongate body and longer dorsal-fin extensions, the genus-typical pattern, though the difference is subtle in this species.
Habitat
Apistogramma caudomaculata is a Guiana-Shield endemic of the lower río Orinoco system in Venezuela. Its type locality is a morichal — a clear-to-blackwater creek shaded and fed by stands of moriche palm (Mauritia flexuosa) — at Pozo Vagabundo near Maripa, on the río Caura, a major right-bank Orinoco tributary in Bolívar State. Its described range extends from the Caura into delta-Orinoco tributaries draining the Serranía de Imataca.
Two contrasting water types are on record, and the fish evidently spans both. The original description sampled it in strongly acidic, very poorly mineralized blackwater morichales — pH about 5.3 to 5.7, conductivity below 10 µS/cm, the soft, tannin-stained, leaf-littered biotope characteristic of the genus. The IUCN account, by contrast, reports it from floodplain lakes and Moriche-palm flooded areas with near-neutral to basic water (pH 6.92, conductivity 60 µS/cm) as well as from acidic blackwater streams and creeks, so the stored pH band of about 4.5 to 6.9 brackets both habitats rather than a single envelope. It is a fish of shallow, still or slow water: the assessment classes its habitat as permanent rivers, streams and creeks plus freshwater marshes and pools under 8 hectares, and notes it at high density in small patches along river littorals. No in-situ depth or temperature figures are published, so the stored depth (0–3 ft) is the habitat-typical shallow littoral and marsh band, and the temperature (about 77–84 °F) is the basin-typical lowland-Orinoco envelope — both inferred rather than measured. The type-locality coordinates given by the Catalog of Fishes (approximately 7.40° N, 65.16° W) should be treated as approximate; the listed longitude contains a transcription artifact, and the curated map point is the corrected type-locality estimate, flagged as approximate.
Feeding
No feeding study exists for Apistogramma caudomaculata. FishBase carries only an estimated trophic level of about 3.3, derived from the size and diet of close relatives rather than from any gut-content analysis of this species. Like other small Apistogramma, it is expected to be a micropredator of the substrate and leaf litter — picking small benthic invertebrates, crustaceans and insect larvae, and sifting fine sediment — but that is a genus-level expectation, not a documented diet for this fish.
Mating
The mating system of Apistogramma caudomaculata has not been observed or recorded. Most Apistogramma are cave-spawning dwarf cichlids with a polygynous-to-haremic social structure: a male holds a territory that overlaps the smaller territories of several females, and pair formation centres on females defending their spawning cavities. Whether Apistogramma caudomaculata follows that common pattern is unknown, and to assume it does is to lean on the genus rather than on any observation of this species.
Breeding
Breeding has not been documented for Apistogramma caudomaculata in the wild or in aquaria. By analogy with the genus it is presumed to be a cave-spawning substrate brooder: the female tends a small clutch inside a sheltered cavity, guarding and fanning the eggs and the wriggling fry while the male defends the wider territory. Apistogramma cave spawners typically lay somewhere in the range of about 40 to 200 eggs, though the actual figure for this species is undocumented. In the genus, fry become free-swimming after roughly a week at typical temperatures and can take newly hatched brine shrimp nauplii and microworms straight away; the female often turns aggressive toward the male once the fry are mobile, and very soft, acidic rearing water can skew sex ratios in the temperature-dependent way recorded for other Apistogramma. Every one of these expectations is inferred from typical Apistogramma biology — no clutch size, spawning behaviour, or fry development has actually been reported for Apistogramma caudomaculata.
In the aquarium
Apistogramma caudomaculata is, as far as anyone knows, absent from the mainstream hobby under its own name: no captive-breeding reports, no trade documentation, no hobbyist literature specific to it. Anyone keeping it works in a genuinely data-thin corner of the genus, where a careful observation adds to the record rather than repeats established practice. With no species-specific guidance to lean on, its blackwater-morichal origin sets the parameters.
Water: the type locality was strongly acidic (pH about 5.3–5.7) and extremely soft (conductivity below 10 µS/cm), so aim for soft, acidic water — pH around 5.5–6.5, hardness as near zero as RO or rainwater cut with a little tap will allow, and a temperature of 77–84 °F.
Tank: a single pair suits roughly 15–20 US gal if caves and sightline breaks give the female refuge; a longer 100–120-litre tank holds one male with two females. At 1.5 in standard length this is a small fish, at the smaller end of the pertensis group, yet the male still claims a territory far larger than his body and will harass females without real cover. Fine sand, a litter of dried leaves (Indian almond, oak, beech), several solid caves (ceramic tubes, coconut halves, stacked slate), subdued light and floating or fine-leaved plants rebuild the biotope. Adults sex easily — males larger, with longer dorsal extensions — juveniles do not.
Tankmates: small soft-water schoolers that settle nerves without crowding the floor — pencilfish (Nannostomus spp.), small tetras such as Hyphessobrycon or Moenkhausia species, or soft-water Corydoras at the same temperature. Avoid robust cichlids, anything big enough to eat an Apistogramma, and hard-water community fish that would force the pH up; other bottom-dwellers such as rival cave-spawners and loaches belong only where the tank is large enough for clearly separated territories.
Common mistake: hard or alkaline tap water rarely kills outright, but it drives chronic stress and washes out colour, and it is the single error most keepers make with blackwater Apistogramma.
Conservation
The IUCN Red List assesses Apistogramma caudomaculata as Least Concern (assessed 2 May 2017, published 2019 under criteria version 3.1; assessor Gabriela Echevarría of the Instituto Venezolano de Investigaciones Científicas, reviewed by C. Sayer). The assessment maps the species to the Guiana Shield in the rivers Candela, Arature, Upata and Caura, with an estimated extent of occurrence of about 30,56 mi²; the Least-Concern verdict rests on that comparatively large range and on several subpopulations facing no apparent threat, which could re-seed any that are affected. Population size is unquantified — there are no abundance estimates, though the species is reported at high density in small patches along river littorals. The one specific documented pressure is illegal gold mining: two illegal mines some 19 mi upstream of the lower-Caura subpopulation (Sanchez 2015) are driving deforestation and pollution, so that subpopulation is judged likely to be undergoing habitat loss and degradation. On the other side of the ledger, the Caura subpopulation falls inside a national park, and roughly 11 to 20 percent of the species' range is estimated to lie within protected areas. The assessment does not know whether the species enters the ornamental fish trade.