Taxonomy & naming
Pterophyllum altum was described by the French ichthyologist Jacques Pellegrin in 1903, in the Bulletin du Muséum National d'Histoire Naturelle, from material in the Paris museum's collection. The type locality is given as the Río Atabapo, a tributary of the upper Orinoco in Venezuela; a syntype is registered in the Natural History Museum, London (NHMUK 1904.6.28.2-3). The genus name combines the Greek pteron ('fin' or 'sail') and phyllon ('leaf'), an allusion to the broad, leaf-like dorsal fin shared across the genus; the specific epithet altum is Latin for 'tall' or 'high,' which is exactly the point of the fish.
The family placement is uncontroversial — it is a Neotropical cichlid (Cichlidae) — but the finer position is rendered differently by different authorities. FishBase, following Kullander's 2003 checklist, lists it in subfamily Cichlasomatinae, while the Cichlid Room Companion places it in subfamily Cichlinae, tribe Therapsini (now usually written Heroini). Either way it sits among the heroine cichlids of South America, alongside discus (Symphysodon) with which it shares both habitat and water chemistry. The trade knows it as the altum angel, deep angel, or Orinoco angelfish. A persistent source of confusion is the so-called 'Peruvian altum,' which is in fact a tall-finned form of Pterophyllum scalare from the upper Amazon and carries none of true altum's ancestry — a marketing label, not a taxon. The genus Pterophyllum holds just three valid species: Pterophyllum scalare, the much more difficult altum, and the less common Leopold's or roman-nose angelfish, Pterophyllum leopoldi (AMAZONAS, Nov/Dec 2021).
Morphology
Altum is built like a coin stood on edge and then stretched skyward. FishBase records a maximum body length of about 7 in and a height of roughly 8 in, but those figures measure the body alone. With the dorsal, anal, and trailing ventral fins fully developed, mature wild fish commonly reach 12–15.5 in from tip to tip; long-term keepers describe adults whose fin span approaches the length of the tank they are standing in. The body is silver to brownish-gold, crossed by three to four dark vertical bars that the fish can darken to jet black or fade to pale cream within seconds depending on mood — a faster and more dramatic shift than scalare manages. All Pterophyllum share the highly laterally compressed, disk-shaped body with wide, tall, sail-like dorsal and anal fins and a large fan-shaped tail (AMAZONAS, Nov/Dec 2021).
The single most reliable feature separating altum from scalare is a deep, pronounced indentation of the snout above the eye (the predorsal notch), which becomes more exaggerated with age. Keepers also point to fin geometry: the trailing edge of the tail in altum is essentially straight to concave with long upper and lower extensions and no barring, whereas scalare shows a more convex tail margin, often barred. Sexes are very hard to tell apart; males may develop a slight nuchal hump around breeding time, but there is no dependable external dimorphism.
Habitat
Pterophyllum altum is a narrow-range endemic of northern South America, straddling two great drainages. The core of its distribution is the upper Orinoco basin along the Colombia-Venezuela border, in tributaries such as the Río Inírida and Río Atabapo up to around Puerto Ayacucho. A second set of populations occurs in the upper Rio Negro, a tributary of the Amazon — a distribution that makes sense given the Casiquiare canal and the deep history of these basins, which were once more directly connected before Andean uplift separated them. This straddling of the Orinoco and the upper Amazon (Rio Negro) is why the species legitimately counts as an Amazon-basin fish even though most trade specimens come out of the Orinoco side. Puerto Inírida, on the Río Inírida in the western drainage of the upper Orinoco, is a major trans-shipment hub for ornamental fishes drawn from the Inírida, Atabapo, Guaviare, and Ventuari rivers (AMAZONAS, Jul/Aug 2021).
The water it lives in is the key to everything about keeping it. These are classic blackwater environments: slow-moving streams, flooded forest margins, and tannin-stained lakes where the water runs the color of strong tea, is extremely soft, and is strikingly acidic. FishBase gives an in-situ range of pH 4.8-6.2 and hardness of 1-5 dH, at tropical temperatures of 81–88 °F (81-88 °F); aquarists and exporters working the Atabapo and Rio Negro routinely report wild pH down into the 4-5 range, water so acidic it is nearly sterile to bacteria. The fish associate with submerged roots, branches, and leaf litter, hanging vertically among structure where their barred, compressed bodies vanish against a background of drowned wood. AMAZONAS field reports describe altums in these blackwater caños keeping a much greater flight distance than the other resident cichlids, and note that troops of adults retreat during the low-water period into atypical granite-rock habitats on the Atabapo, away from the flooded forest to which they are otherwise adapted (AMAZONAS, Jul/Aug 2021).
Feeding
Altum is a mid-water, structure-associated predator of small prey rather than a grazer. FishBase estimates a trophic level of about 3.3, consistent with a diet built around aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and the like — supplemented by tiny fish and whatever drifts within reach of an ambush from cover. The deep, flattened body and the habit of hanging among roots are the marks of a sit-and-wait hunter that picks prey from the water column and from submerged surfaces rather than chasing it in the open.
In the nutrient-poor blackwater it inhabits, that opportunism matters: blackwater rivers are famously low in dissolved minerals and primary productivity, and much of the food base is allochthonous — falling in from the surrounding flooded forest as insects, fruit, and detritus. Angelfish there are part of a community that includes discus, smaller characins, and dwarf cichlids, partitioning the flooded-forest edge by depth and feeding style. The aquarium correlate is well known: wild-caught altums often refuse dry food at first, are strongly drawn to live and frozen invertebrates, and only gradually accept prepared diets.
Mating
Socially, altum is comparatively peaceable for a cichlid. In the wild and in large aquaria the fish form loose shoals, and multiple long-term keepers independently note that altums are less prone to the constant pecking and chasing seen among adult scalare — though anything small enough to fit in the mouth, down to neon tetras and fry, is still fair game. Within a group a hierarchy forms and a bonded pair will eventually break away from the shoal to claim and defend a spawning site, but the species does not show the relentless territoriality of many African cichlids.
Pairs are self-selecting: rather than being matched by the keeper, two fish from a group settle on each other over time, which is one reason a small shoal is the usual route to a pair. Courtship centers on a chosen vertical surface — a broad leaf, a root, or the aquarium glass — which the pair clean together in the run-up to spawning. Telling a forming pair apart by sex is difficult; there is no reliable external dimorphism, and the bond often becomes obvious only once the two fish begin jointly defending their patch.
Breeding
Reproduction is substrate spawning with biparental care, not mouthbrooding: a bonded pair lays a sheet of adhesive eggs on the cleaned vertical surface, and both parents fan and guard the clutch and, once they hatch, the wriggling larvae. This biparental substrate-spawning mode is shared across Pterophyllum, but in altum it is rarely seen in captivity.
Breeding in aquaria is genuinely difficult and is the chief reason true altums remain rare in the trade. The consensus across specialist and hobby sources is that successful spawning requires very soft, very acidic water; even keepers who maintain healthy adults for years often never see a pair form, and reports of captive spawns frequently involve artificially raising the fry away from the parents. Seriously Fish notes, against the grain of some care sheets, that altums have been bred without artificial fry-rearing — but it remains an achievement, not a routine outcome. Almost all altums in the hobby are therefore still wild-collected, sought out mainly by breeders and advanced aquarists chasing geographic variants (AMAZONAS, Nov/Dec 2021).
In the aquarium
This is not a beginner's fish, and honest sources are unanimous on the point. The first hurdle is the supply chain: nearly all altums in the trade are wild-caught from the Orinoco during a short collecting season — the peak low-water weeks of January and early February, when fish concentrate in the residual waters — and they pass through several hands and a long journey before export, arriving stressed and prone to bacterial infections (AMAZONAS, Jul/Aug 2021; June 2024). The practical lesson from people who have done it is to buy well-started juveniles rather than tiny or very large fish, and to prioritize a dealer who has already conditioned and acclimated the stock. There is also a useful, counterintuitive insight from the trade (notably from AMAZONAS reporting): because exporters gradually raise the pH of holding water before shipping, dropping fresh imports straight back into extremely low-pH blackwater can shock them — matching the seller's actual parameters matters more than chasing wild values, and temperatures above about 82 °F can accelerate bacterial problems in newly arrived fish.
Give them height. A tank around 6 ft (6 ft) long and at least 24 in (23.5 in) — better 30 in (29.5 in) — tall is a realistic minimum for a small group; shorter tanks damage the trailing fins and stress the fish. Water should be soft and acidic, with the strong caveat that stability beats any specific number: keepers report success anywhere from pH 5 to neutral provided the value is steady and dissolved organics are kept very low through heavy, frequent water changes and (for wild fish) RO water acidified with leaf litter. A minority of keepers report holding wild altums long-term in neutral tap water, which shows individual variation, but the dominant experience is that pH swings, high conductivity, and nitrate buildup kill them. They suit a quiet, dimly lit, planted or root-filled biotope tank, ideally alongside discus or other soft-water natives, and emphatically not boisterous tankmates.
Conservation
The IUCN Red List assessed Pterophyllum altum as Least Concern. The assessment was carried out on 28 October 2020 by Carlos Lasso and published in 2023. The justification rests on its relatively wide distribution from the upper Orinoco through the Inírida region across the Venezuela-Colombia frontier, which buffers the species against localized impacts. So the species itself is not, at present, considered threatened with extinction.
That said, the assessment and the specialist literature flag real, specific pressures rather than a clean bill of health. Because altum is a high-value ornamental species, it carries genuine collection pressure, and the IUCN account notes the threat from illegal mining in its range — gold mining in particular brings sedimentation and mercury contamination to these otherwise clear, nutrient-poor blackwaters. In response, Colombia's fisheries authority imposed a closure beginning in January 2020 that prohibits capture of the species within the country, which also blocks Colombian collectors from re-exporting Venezuelan fish. A Colombian regional red list cited through GBIF even flags the species as Vulnerable at that national scale, a reminder that a globally secure fish can be locally strained.
Placed in its wider setting, this fits the broader picture of Neotropical cichlids documented in the regional checklist literature (Kullander's 2003 Check List of the Freshwater Fishes of South and Central America; Lowe-McConnell's work on tropical river fish communities): most Amazon and Orinoco cichlids are Least Concern or Not Evaluated and face ornamental-trade collection and habitat change — deforestation, mining, sedimentation — rather than population collapse. Notably, the collection of altums by indigenous communities along the Inírida, Atabapo, and middle Orinoco is described in the field literature as a significant and largely sustainable source of livelihood (AMAZONAS, Jul/Aug 2021; June 2024). The altum's vulnerability is therefore narrower and more specific than 'endangered': it is a specialist of soft, acidic blackwater, a chemistry that mining and watershed disturbance degrade directly, and a fish whose appeal makes it a steady target for collectors. Least Concern, in other words, with watchpoints worth taking seriously.