Taxonomy & naming
Australoheros angiru was described in 2011 by Oldřich Říčan and Lubomír Piálek of the University of South Bohemia together with Adriana Almirón and Jorge Casciotta of the Universidad Nacional de La Plata, in a Zootaxa paper (2982: 1–26) that erected two new species — Australoheros angiru and Australoheros ykeregua — and reassessed the diversity of the whole genus across the Río de la Plata basin. (Note: this corrects a common misattribution to Říčan & Kullander 2008 or to Ottoni; those authors named other Australoheros, but angiru is a 2011 Říčan, Piálek, Almirón & Casciotta species.) The holotype, MCP 13937, is a 3 in SL fish from the rio Jacutinga in the rio Uruguai drainage of Santa Catarina, Brazil, taken along highway BR-283 between Ceará (Itá) and Concórdia; it is held, with the paratype series of thirteen specimens (1–3 in SL), in the fish collection of the Pontifícia Universidade Católica do Rio Grande do Sul in Porto Alegre (acronym MCP). Additional, non-type material extends the species west into the rio Iguaçu drainage of Paraná state. The genus Australoheros was itself created by Říčan & Kullander in 2006 to receive the southern, temperate-to-subtropical 'chanchitos' long dumped into the wastebasket genus Cichlasoma; the name joins Latin australis, 'southern', to Heros, the type genus of the tribe Heroini. The describers place angiru as the sister species of Australoheros minuano on DNA evidence, even though it had previously been lumped with the superficially similar Australoheros kaaygua — the confusion that gives the fish its name. Part of the type-era material (lot MCP 6262) had earlier been misidentified, in Říčan & Kullander (2008), partly as Australoheros kaaygua and partly as Australoheros forquilha, which is why untangling angiru required both fresh collecting and molecular work.
Morphology
Australoheros angiru is a small, notably deep-bodied cichlid. The type series runs from about 1–3 in in standard length, and FishBase lists a maximum of 3 in SL drawn directly from that material — so this is a palm-sized fish, smaller than the better-known chanchitos, with no evidence yet of much larger wild adults. Its single most diagnostic proportion is depth: at a mean body depth of 49.6% of standard length it is one of the deepest-bodied species in the genus, a build it shares only with Australoheros guarani and Australoheros facetus. The snout is short and straight in profile, the jaws isognathous (upper and lower meeting evenly), and the mouth small and terminal to slightly subterminal — a feature that separates it from the large, supraterminal mouth of its sister species Australoheros minuano. Fin and scale counts from the description and FishBase give sixteen to seventeen dorsal spines, eight to ten soft dorsal rays, six to eight anal spines, six to eight anal soft rays, and 26–27 vertebrae. Live colour is best documented from the rio Iguaçu populations photographed by Wolfgang Staeck: a clean yellow ground crossed by dark vertical bars and a dark horizontal stripe, with the genus's typical large, dominant midlateral blotch but only a very narrow or absent spot at the caudal base. The iris is yellow — unusually so, and a useful field mark against the dark-green eye of Australoheros kaaygua — and the caudal fin carries red dorsal and ventral margins and corners. In breeding dress the fish takes on the standard Australoheros pattern, in which the dark vertical bars are interrupted in their upper portion between the gill cover and the midlateral blotch; ripe, breeding females additionally develop a black blotch in the dorsal fin. Sexual dimorphism otherwise follows the genus: males grow somewhat larger and longer-finned, females become rounder-bodied when in spawning condition.
Habitat
Australoheros angiru has a curiously disjunct distribution that the describers read as a fingerprint of river-capture history. It occurs in two separated areas: the middle rio Iguaçu drainage of Paraná, southern Brazil (with collections from the rio São Pedro and rio Iratim near Pinhão and Palmas, on the Paraná plateau), and the upper rio Uruguai drainage of Santa Catarina, where the type locality on the rio Jacutinga lies; a single locality is also known from the middle río Uruguay in Misiones province, Argentina. These two clusters bracket the divide between the Iguaçu and upper Uruguai basins, and Australoheros distributions across exactly this boundary are part of the biogeographic argument the paper builds for former connections between today's isolated drainages. This is upland, subtropical southern South America — the Brazilian-shield headwaters above the great Iguaçu and Salto Caxias falls — not the tropical Amazon: the fish belongs to clear, often cool plateau streams rather than warm lowland rivers. The IUCN assessment records it from inland wetlands and permanent rivers, streams and creeks, with the type material from the rio Jacutinga. No in-situ water chemistry, depth profile or temperature has been formally published for the species; FishBase tabulates it simply as a tropical, freshwater, benthopelagic fish without a depth range. The temperature, pH and depth values in the fact boxes here are therefore flagged genus-typical estimates rather than measured field data — drawn from the documented husbandry envelope of the southern, cold-tolerant chanchitos (roughly 64–82 °F, pH about 6.5–7.5) and from a shallow plateau-stream depth band (about 0–7 ft), consistent with a small subtropical-upland cichlid that experiences a real seasonal cool-down rather than constant tropical warmth. Where a number is an inference of this kind it is called out as such; nothing here is presented as a measurement that does not exist.
Feeding
No dedicated diet study has been published for Australoheros angiru, so its trophic role is inferred from FishBase and from the well-known ecology of the genus. FishBase places it at a trophic level near 3.2 — the band of a small omnivore that tilts toward animal prey — and rates its fishing vulnerability as low. Like the other chanchitos it is a substrate-oriented forager of small streams: a fish that grubs through soft sediment, sand and leaf litter and works the margins of submerged vegetation, taking aquatic insect larvae and other small invertebrates along with incidental algae, plant matter and detritus picked up in the process. Its small, terminal mouth and isognathous, grasping jaws suit a generalist that picks and dislodges small prey rather than a specialist that crushes shells or rasps algae from rock. In its plateau streams it functions as a mid-level benthic omnivore — neither a dedicated predator nor a herbivore — a typical role for a small heroine cichlid in a cool, clear-water headwater community.
Mating
Reproductive behaviour has not been described for Australoheros angiru in the wild, but the genus is consistent enough that the broad picture is secure, and Wolfgang Staeck (1998, 2003) documented the spawning and behaviour of Iguaçu-drainage angiru under aquarium conditions — among the few first-hand accounts of the species at all. Australoheros are pair-forming, territorial substrate spawners: a male and female establish and jointly defend a patch of bottom, and courtship is accompanied by the intensified, bar-broken breeding livery typical of the genus, with the female of this species developing a distinct black blotch in the dorsal fin. Pairs grow markedly more aggressive and site-attached as spawning nears, excluding conspecifics and other fishes from the chosen territory. As in related chanchitos, a seasonal shift — cooling through the subtropical winter followed by warming and the onset of the rains — is the natural cue that brings fish into breeding condition, which keepers reproduce with a cool rest period followed by a temperature rise and generous live feeding.
Breeding
Australoheros angiru is a biparental, open substrate spawner like the rest of its genus; Staeck's aquarium accounts confirm this for the species directly, and the finer numbers are read across from its better-documented relatives. No clutch count specific to angiru has been published — the figure given in the fact box is labelled genus-typical, drawn from congeners such as Australoheros facetus, which deposit a few hundred adhesive eggs (commonly on the order of 200–500, more in a large, well-conditioned female) on a cleaned firm surface: a flat stone, a root or the floor of a shallow pit. Care is shared. The female tends and fans the eggs while the male patrols and defends the territory, and after the eggs hatch both parents guard and shepherd the free-swimming fry, herding them between feeding pits in the substrate; the female's dark breeding pattern and dorsal-fin blotch are part of the brooding signalling. Spawning is cued by warming the water after a cooler resting period, mimicking the seasonal warming of the natural plateau streams, and because angiru is a cool-tolerant subtropical fish rather than a tropical one it can be conditioned and bred with the winter cool-down itself serving as the rest phase. The fry are not difficult to raise on small live and prepared foods once the pair has brought them up — the harder part, as with most chanchitos, is keeping a bonded pair from turning on each other or on tankmates when in spawning mood.
In the aquarium
Australoheros angiru is a rarely kept fish and practically absent from the mainstream hobby outside of a small circle of cichlid specialists who keep South American substrate spawners. Its closest analog in the trade is the much better-known chanchito, Australoheros facetus, and keepers who have experience with that species or with other southern Australoheros will find the care requirements broadly familiar. Where species-specific data are thin, the following account generalizes from congeners and says so plainly.
A single pair or a solo specimen can be maintained comfortably in an aquarium of about 35.5–47 in (roughly a 100–150-litre footprint), though a breeding pair with territorial ambitions will use every centimetre of that space and push smaller tankmates hard. Because angiru is a deep-bodied fish from cool plateau streams rather than from warm tropical lowlands, it handles temperatures between about 18 and 82 °F and genuinely benefits from a seasonal cool-down: dropping the heater to 64–68 °F over the autumn and winter months mimics the fish's natural environment and conditions it for spring breeding, whereas sustained tropical temperatures at the upper end of that range are probably harder on the fish over the long term than the cool end. Water chemistry in the fact box reflects the soft, near-neutral to mildly acidic conditions of the upland Paraná–Uruguay watershed (pH 6.5–7.5); the fish is tolerant rather than demanding, and ordinary conditioned tap water in that range will keep it well.
Substrate should be fine sand or fine gravel — the fish forages by sifting and rooting through the bottom, and rough gravel frustrates that behaviour. Flat stones, smooth slabs or pieces of smooth wood provide the cleaned spawning surfaces the pair will select when breeding; caves are less relevant than open surfaces. A moderate amount of cover — driftwood, a few robust plants, ceramic pipe sections — is useful for giving less dominant fish an escape from the pair when their territorial drive peaks, but the tank should not be so densely planted that the pair has nothing to defend; they need a defined open territory to be settled and secure.
Tankmate choice is the main management challenge with this species. Like most chanchitos, Australoheros angiru is peaceable for most of its life but becomes a serious aggressor around spawning time, and a breeding pair will claim the whole aquarium and pressure anything else in it relentlessly. Keeping it in a species tank or with only one or two comparably sized, robust dither species — other subtropical South American fish such as some of the larger tetras, or similar-sized cichlids that can hold their own — is safer than a community approach. Small or slow-moving tankmates, and anything that encroaches on the pair's chosen spawning site, will be chased hard and can be badly damaged. Conspecifics need to be watched: a mismatched pair where one fish has rejected the other will produce a battered victim, and two males will fight persistently.
The main mistakes keepers make with this species and its genus are keeping it too warm year-round, understocking the tank relative to the pair's territorial footprint, and misjudging how abruptly the pair's temperament shifts around breeding. The fish are not difficult to maintain or condition — Australoheros angiru is a robust, adaptable small cichlid that eats freely and takes standard foods including quality pellets, frozen bloodworm, daphnia and small live invertebrates — but their relatively low availability means that when pairs are obtained they are often housed in tanks that are too small, too densely stocked, or too warm. Breeding is achievable in captivity: Staeck documented spawning in Iguaçu-drainage angiru under aquarium conditions, the pair following the standard Australoheros pattern of biparental care in which the female fans and broods the clutch while the male holds the perimeter, and both parents herd the free-swimming fry. Fry take microworms and baby brine shrimp without difficulty once parental care is running.
Conservation
The IUCN Red List assesses Australoheros angiru as Least Concern (assessed 4 November 2020 by R.G. Frederico, reviewed by T.J. Lyons, published 2023; e.T162857505A162857512). The justification is straightforward: despite little being known about the species and the presence of potential threats within its range, it is listed as Least Concern on account of a comparatively large distribution — an estimated extent of occurrence of about 186,0 mi² spanning the Iguaçu and upper-to-middle Uruguay basins of Brazil (Paraná, Santa Catarina, Rio Grande do Sul) and Argentina. That status comes with honest caveats from the assessors themselves: population size and trend are unknown, the fish is noted as 'not very frequent or abundant', and it carries no CITES or CMS listing and no documented use or trade. (An older Cichlid Room Companion note still records the species as not evaluated; that simply pre-dates the 2020/2023 Red List assessment.) The threats the assessment flags are habitat-level rather than species-specific: the species' range is strongly impacted by dams and water management and by housing and urban development. Those pressures are real for this fish in particular. The Iguaçu and upper Uruguai are among the most heavily dammed rivers in South America — a cascade of large hydroelectric reservoirs (Salto Caxias, Salto Santiago, Foz do Areia and others on the Iguaçu; Itá, Machadinho and Foz do Chapecó on the upper Uruguai) has converted long reaches of free-flowing plateau river into still impoundments, fragmenting populations and erasing the small-stream and headwater habitats a fish like angiru depends on, while agriculture and urbanization add siltation, riparian clearing and run-off. A small, patchily distributed upland endemic with no documented abundance is exactly the kind of fish whose Least Concern listing rests on range size rather than on any evidence of security — its long-term status should be read against that heavily modified basin, and a proper population study remains an outstanding need.