Taxonomy & naming
Tahuantinsuyoa macantzatza was described by the Swedish ichthyologist Sven O. Kullander in his 1986 monograph Cichlid Fishes of the Amazon River Drainage of Peru, the work that reshaped the systematics of Peruvian cichlids. He simultaneously erected the genus Tahuantinsuyoa for it, designating macantzatza as the type species by original designation; the genus was monotypic at description. The holotype (MZUSP 16212, in the Museu de Zoologia da Universidade de São Paulo) came from the Río Huacamayo in the Río Aguaytía drainage, Departamento Ucayali, Peru, with an extensive paratype series spread across the São Paulo, Stockholm (NRM), Geneva (MHNG), Chicago (FMNH) and Copenhagen (ZMK) collections. Eschmeyer's Catalog of Fishes lists no synonyms — the name has stood unchallenged since 1986 and is repeatedly confirmed as valid (Kullander 1991, Kullander in Reis et al. 2003, Meza-Vargas et al. 2021, Chuctaya et al. 2022). In 1991 Kullander described a second species, Tahuantinsuyoa chipi, from the neighbouring Pachitea drainage, so the genus is no longer monotypic; the epithet chipi is the Shipibo word for 'sister,' a deliberate nod to the close, next-river geographic relationship between the two. The genus sits in the subfamily Cichlinae, tribe Cichlasomatini, among the heroine and acara-like cichlids of South America rather than the eartheaters; its precise relationships within that group continue to be refined by molecular phylogenies. In the field the species is easily mistaken for Bujurquina, the larvophilic mouthbrooders that were themselves once lumped into Aequidens before being split out — both groups share a superficially similar slender build and a dark head stripe. The reliable field mark is the stripe's orientation: in Bujurquina it runs forward, between the eyes; in Tahuantinsuyoa macantzatza it starts at the eye and runs backward, toward the dorsal fin — the character a field party used, working from Kullander's 1986 key, to identify their first Aguaytía-drainage catch of this species as Tahuantinsuyoa rather than a Bujurquina (Cichlids Yearbook, Vol. 1).
Morphology
The Inca stone cichlid is a moderately sized, elongate, ovate and laterally compressed cichlid. FishBase gives a maximum length of about 4.5 in total length, drawn from the original description, and hobbyist accounts put well-kept males at roughly 5 in or a touch more; the largest measured type specimen is a 3 in SL female, so females clearly run smaller than males. Base coloration is a pale, silvery grey overlain by a dense scatter of golden and bluish-opalescent dots arranged in irregular longitudinal rows, with a dark blotch (the 'midlateral spot' typical of many cichlasomatines) on the flank. In display the fish is a genuine riot of colour — the well-developed dorsal fin flushes with blue and azure, and patches of red develop on the fins and body. Like discus and many other cichlids it can throw a pattern of dark vertical bars across the body when stressed or sparring — six of them, running the length of the flank, sharpest when the fish is excited. The head carries a rather heavy, thick-lipped profile for so slender a body, and the unpaired fins are rounded in both sexes, not a dimorphic trait. Sexual dimorphism is modest but real: males grow slightly longer, carry more massive heads, and are the more vividly coloured sex, while ripe females are deeper-bodied and plainer. The species' alert, almost nervous bearing — it is a near-constant swimmer that holds to the lower and middle water levels — is as diagnostic in life as any single fin or marking.
Habitat
Tahuantinsuyoa macantzatza is endemic to the Río Aguaytía system, a tributary of the Río Ucayali in the upper Amazon basin of east-central Peru (Departamento Ucayali), on the Andean piedmont. The IUCN puts its extent of occurrence at under 20,000 square kilometres, making this a genuinely range-restricted, single-drainage fish (its sister species Tahuantinsuyoa chipi replaces it one drainage over, in the Pachitea). The epithet itself records the biotope: the bed of the type-locality stream, the Río Huacamayo, is predominantly stony, and the fish is characteristically found in well-oxygenated, briskly flowing foothill waters over substrates of gravel, stone and sand. The IUCN assessment describes it living in rivers and streams of black and mixed waters. FishBase records an in-situ chemistry of pH 6.3 to 7.7 and very soft water (about 2 to 2.5 °dH) at temperatures of roughly 77–82 °F — the warm, soft, slightly acidic-to-neutral profile expected of a clearwater/blackwater piedmont stream. As a shallow-stream demersal fish it occupies the upper few metres of the water column; no precise depth range has been published, so a habitat band on the order of 0–10 ft is a reasonable inference rather than a measured figure.
Feeding
The Inca stone cichlid is an omnivore. The IUCN assessment, summarising the available natural-history information, records a diet of fruit, submerged plants and aquatic invertebrates — a generalist's mix of plant and animal material worked from the stony stream bed and the water column above it. FishBase places it at a trophic level of about 3.2, consistent with an omnivore tilted modestly toward animal prey rather than a dedicated piscivore or strict herbivore. In captivity the species confirms this opportunism: it accepts essentially any food offered, from live and frozen invertebrates (glassworms, mosquito larvae, whiteworms) to vegetable matter such as spirulina and to prepared dry foods. Notably, despite holding to the lower levels of the tank it feeds readily at the surface, darting up in a shoal to snatch floating items — a flexibility in foraging height that matches its restless, active habits in flowing water.
Mating
Outside of reproduction Tahuantinsuyoa macantzatza is a sociable, shoaling fish and broadly peaceful, though mature males will skirmish over territory and these squabbles intensify as breeding approaches. Pairs form from within a group as fish reach maturity; a forming pair stakes out and defends a territory, repeatedly driving the rest of the shoal away. Courtship is the classic cichlid sequence of reciprocal display — the male leads, tautening his body and intensifying into spawning colour, and both fish perform a prolonged 'dance,' shivering obliquely with heads down and fins spread, that can last several hours. Hobbyist observation suggests this species spawns in calm rather than fast water: although it lives in briskly flowing streams, breeding is reported to take place in standing or slack-water pockets, and reducing flow and the frequency of water changes is a recognised trigger. The pair bond is cooperative through spawning and the early care of young, with both parents taking active roles.
Breeding
Tahuantinsuyoa macantzatza is a larvophilic biparental mouthbrooder — an unusual mode that blends substrate spawning with mouthbrooding. The pair first cleans and tests a movable substrate: in the wild this is typically a fallen leaf or a piece of wood, and in aquaria the fish will use submerged leaves (catappa, beech, oak), thin chips of coconut shell, or, failing those, a stone or root. Eggs roughly 0.5 in in diameter are laid a few at a time and fertilised by the male over the course of up to an hour; clutches are small, generally only a few dozen eggs, which also approximates the eventual brood size. Crucially, once spawning is complete a parent takes the egg-laden leaf or chip in its mouth and carries it to a secluded, hidden location — sometimes dusting it with sand for camouflage or turning it over. After a few days the larvae hatch and are taken into the parents' mouths; FishBase records that both parents guard the eggs and take the larvae in the mouth, though hobbyist accounts note that sometimes only one parent incubates. The free-swimming fry begin foraging within days and can be raised on microworms and baby brine shrimp; at any threat the parents scoop them back up. Diligent biparental care continues for roughly a month before the young become fully independent.
In the aquarium
The Inca stone cichlid is a rewarding but uncommon aquarium fish, traded sporadically and usually as captive-bred stock a generation or two from the wild rather than as wild imports. It is an energetic, almost restless cichlid that swims constantly, so footprint matters more than height: a tank of at least about 35.5 in long, and ideally longer, suits a pair or small group, with the emphasis on length and width over depth. Because the fish naturally pairs out of a shoal, many keepers start with a group of young and let a pair form, accepting that mature males will spar over territory.
Water chemistry is forgiving within the species' warm, soft envelope. It does well across soft to moderately hard water at pH 6.3 to 7.7 and temperatures of roughly 75–84 °F (75–85 °F), which makes it more adaptable than many specialist Amazonians. Even so, it rewards a biotope-style setup that mirrors its piedmont-stream origins: a substrate of sand and gravel with smooth stones, driftwood and rock hideouts to define territories, efficient filtration and aeration to keep metabolites low, and regular partial water changes. Keepers commonly soften and gently acidify the water with peat or botanicals (Indian almond/catappa leaves), which also supply tannins and humic compounds useful at breeding time. Avoid heavy overfeeding — the species is greedy and prone to it.
Temperament is community-compatible with sensible stocking. Inca stone cichlids are peaceful toward tankmates large enough not to be eaten, and have been kept successfully alongside larger Apistogramma and similar mid-sized South Americans; the main caveats are occasional male-on-male territoriality, which sharpens during breeding, and the risk that very small fish or shrimp will be treated as food. For breeding, provide several movable spawning substrates — catappa or other sturdy leaves are ideal — so the pair can select and relocate one; reduce flow and stretch out water changes to simulate the slack water in which they prefer to spawn. Watching the leaf-carrying, larvae-mouthing reproductive ritual is, for many keepers, the whole point of the species.
Conservation
The IUCN Red List assesses Tahuantinsuyoa macantzatza as Data Deficient (assessed 21 April 2014, published 2016; assessors Velasquez, Hidalgo del Aguila & Chocano), reflecting the absence of sufficient information on its extent of occurrence, natural history, threats and conservation status. The single-drainage range is small — an extent of occurrence under 20,0 mi² — and the species reassuringly occurs within at least one protected area, Parque Nacional Cordillera Azul. The chief documented pressure is in the Río Aguaytía itself, where deforestation for timber and agriculture drives erosion, sedimentation and elevated nutrient loads, degrading water quality at one or more of the fish's localities; the assessment notes a corresponding continuing decline in habitat quality there. Locally the species is taken in small numbers as a protein source, and it appears occasionally in the ornamental trade, but neither is flagged as a population-level threat. It carries no CITES listing. The assessment is annotated as needing updating, and explicitly calls for further study of the species' distribution, abundance, breeding biology, ecology and threats — the kind of targeted work that would let a future assessor move it off the Data Deficient list.