Taxonomy & naming
Australoheros sanguineus was described by the Brazilian ichthyologist Felipe P. Ottoni in 2013, in the journal Vertebrate Zoology (63(2): 161–169), on a series of eleven specimens collected in the rio Cubatão basin around Joinville. The holotype — a 3.5 in standard-length fish, register MCP 14556 in the collection of the Pontifícia Universidade Católica do Rio Grande do Sul — came from the arroio Lindo, a small tributary of the rio Cubatão near the SC-301 and BR-101 highways at Pirabeiraba, Joinville municipality, Santa Catarina state. Eschmeyer's Catalog of Fishes lists the name as valid, a status upheld by every subsequent treatment of the genus (Říčan et al. 2016; Ottoni et al. 2019; Lucena et al. 2022); it is a good species, not a synonym. The genus Australoheros was erected by Říčan & Kullander in 2006 to hold the southern, temperate-edge heroine cichlids long lumped under 'Cichlasoma' facetum, and it has since ballooned into the most species-rich genus of the tribe Heroini and one of the largest in the subfamily Cichlinae. Ottoni placed sanguineus among the coastal Atlantic-forest species of south-eastern and southern Brazil rather than with the inland Paraná–Uruguay–Paraguay groups (the facetus, scitulus, forquilha and kaaygua groups of Říčan & Kullander). The fish carries no established English or Portuguese common name; in the broader hobby the genus is loosely called 'chanchita' or 'chanchito', a River Plate vernacular borrowed from the better-known Australoheros facetus, but that name is not specific to this species and is not used as a formal alias here.
Morphology
This is a small cichlid: the type series ran from about 2.5–4 in in standard length, and FishBase rounds the maximum to roughly 4 in SL — a fish that, including the tail, sits comfortably in the palm of a hand. The body is deep and laterally compressed, the head profile gently curved, with a terminal, roughly even-jawed (isognathous) mouth set with slightly inward-curving caniniform teeth that Ottoni noted are tipped red. Live fish are a yellowish brown crossed by seven darker bars and three black blotches — one rounded spot on the caudal-fin base, one where the mid-body longitudinal stripe meets the fourth trunk bar, and one on the rear edge of the gill cover — overlaid with green-and-blue iridescence concentrated along the flank stripe. The diagnostic feature, and the source of the name, is colour at the tail: two distinct blood-red zones at the upper and lower corners of the caudal fin's trailing edge, set against a yellow-to-greenish caudal fin and a conspicuous blue iridescent bar along the dorsal-fin margin. Several congeners show reddish pigment on the tail, but in sanguineus it is a true blood red rather than a diffuse blush, and unlike the closely similar Australoheros acaroides and Australoheros facetus it lacks any red line running along the dorsal-fin edge. Beyond colour, Ottoni separated it on a suite of counts and proportions: fourteen pectoral-fin rays (more than most relatives), a comparatively long and deep caudal peduncle, a longer snout and broader interorbital than the southern Australoheros facetus, Australoheros guarani and Australoheros minuano, and details of where the scaly sheath begins along the dorsal and anal fin bases. Sexual dimorphism was not documented in the original description, which worked from preserved museum material; in Australoheros generally the sexes are similar, with males tending to grow somewhat larger and to develop more pointed, extended dorsal and anal fins, so any difference in sanguineus is expected to be modest and is noted here as genus-typical rather than measured.
Habitat
Australoheros sanguineus is endemic to Brazil and, as far as is known, to a small cluster of coastal river basins in the north of Santa Catarina state. The type basin, the rio Cubatão, is an isolated coastal drainage of only about 306 mi²; it rises near 1,328 ft on the Serra Queimada in the Atlantic-forest mountains and falls to the sea at the Baía da Babitonga, the estuary fronting Joinville. Eschmeyer's Catalog of Fishes gives the range as the Cubatão together with the neighbouring rio Piraí and rio Iguaçu basins of this same coastal sector of southern Brazil — drainages that flow to the Babitonga rather than to the distant Paraná-system Iguaçu, a separate river that shares the name. The IUCN assessment adds that more recent records further south in Santa Catarina suggest the species is somewhat more widespread in the state than the type material implied, though it is hard to tell apart from its congeners and its true distribution remains poorly mapped. These are clear, often soft-water coastal streams and rivers of the Atlantic forest; FishBase classifies the fish as freshwater and benthopelagic. No in-situ water chemistry, temperature or depth has been published specifically for sanguineus — the IUCN account states plainly that there is no information on its habitat and ecology — so the figures in the fact box are drawn from its better-studied congener Australoheros facetus and from the temperate-subtropical character of these southern coastal basins: roughly 77–86 °F, near-neutral pH around 6.5–7.0, moderate hardness, and the shallow water (on the order of 0–7 ft) of small rivers and streams. They should be read as genus- and habitat-typical estimates, flagged as such, not as measurements from this species. One thing the latitude does tell us: as the southernmost heroine cichlids, Australoheros experience cooler, more strongly seasonal water than the equatorial cichlids of the Amazon, and tolerate it well.
Feeding
No diet study has been carried out on Australoheros sanguineus itself, and its trophic level on FishBase (about 3.2) is estimated from the size and relatives of the fish rather than from gut contents. Its feeding can be read off the genus, which is consistently described as omnivorous. The well-documented Australoheros facetus is an opportunistic, diurnal forager that takes detritus and plant material along with small aquatic animals, including the occasional small fish, working the bottom and the lower water column of creeks, rivers, swamps and lakes. The caniniform teeth and moderately deep body of sanguineus fit that same generalist mould: a fish that grazes and gleans benthic invertebrates and organic matter rather than a specialist sand-sifter or piscivore. In its coastal-stream community it is best thought of as a mid-level benthic omnivore.
Mating
The courtship of Australoheros sanguineus has not been observed and reported, but the genus is uniform enough in its reproductive style to sketch the likely pattern with confidence. Australoheros are substrate-spawning cichlids that form monogamous pairs at breeding time, with both sexes defending a territory. In Australoheros facetus, pair formation precedes spawning and both partners become territorial around a chosen hard surface; spawning is triggered by warming water, above roughly 82–86 °F in the populations that have been watched. The same biparental, pair-bonding territoriality should be expected here. As with most pair-spawning cichlids, the practical consequence for anyone keeping them is that aggression peaks at breeding time, when a bonded pair will drive other fish away from the nest site, while outside the breeding season the species is comparatively undemanding socially.
Breeding
Breeding has not been documented for Australoheros sanguineus in the wild or, so far as the published record shows, in aquaria, so what follows is the well-established genus pattern, flagged as such rather than observed in this species. Australoheros are open or substrate spawners: the female deposits her eggs on an exposed hard surface — a flat stone or a piece of submerged wood — rather than hiding them in a cave or carrying them in the mouth. Both parents then care for the clutch, guarding and fanning the eggs and shepherding the larvae and free-swimming fry, with parental care in Australoheros facetus lasting on the order of one to three weeks. Fecundity in that congener runs to a few hundred eggs (figures around 300–1,000 have been reported), which is a reasonable expectation for a fish of this size; sanguineus, being smaller, likely sits toward the lower end. Spawning is cued by rising temperature, mirroring the seasonal warming of its subtropical home streams. None of the egg counts, developmental timings or fry-care details has been measured for sanguineus specifically, and they are given here as genus-typical values.
In the aquarium
Australoheros sanguineus is almost unknown in the hobby — it has never been established in the aquarium trade, and any fish circulating under this name should be treated with skepticism given the difficulty of separating it from similar-looking congeners. What follows draws on the well-documented care of Australoheros generally, and of Australoheros facetus in particular, with the species-specific facts (size, temperature range, water chemistry) applied where relevant. It is accurate to the genus; keepers fortunate enough to obtain confirmed specimens should not expect much to differ.
A tank of at least 25–30 US gal is suitable for a pair, with a longer footprint preferred over height — these are bottom-oriented fish that spend most of their time in the lower third of the water column. The substrate should be fine to medium sand or small gravel, and the hardscape should include flat stones and pieces of smooth root or bogwood to serve as potential spawning surfaces; the fish will also appreciate scattered planting, though they will dig and may uproot soft-stemmed species around the nest site. Subdued lighting and some visual cover help the pair settle. Being from coastal Atlantic-forest streams, the species is comfortable at 77–86 °F; because its home basins sit at roughly 26° south latitude, it tolerates seasonal dips into the low 20s better than most tropical cichlids, so room-temperature keeping in a warm home is feasible for short periods. Target pH 6.5–7.0 and soft to moderately hard water (below about 12 °dH); municipal tapwater in many temperate cities falls naturally in this range, which partly explains why the broader chanchito group has long been a keeper's fish in South America and Europe.
Tankmates should be chosen carefully. Like all Australoheros, sanguineus is a pair-bonding cichlid that becomes territorial and can be aggressive when breeding, and the combination of a small tank footprint, a bonded pair, and a hard-surface nest can be dangerous for anything else in the water. Outside the breeding season the fish is reasonably tolerant, and robust, similarly sized companions — larger characins, loricariid catfish, or other temperate South American species — can coexist if the tank is adequately sized and broken up with decor. Conspecifics and close congeners should be avoided unless a significantly larger tank is used; males in particular are likely to fight. Delicate or slow-moving fish are poor choices at any time.
Spawning follows the standard Australoheros pattern: the pair cleans a flat, hard surface and the female deposits adhesive eggs in rows, with both parents immediately defending the site. Broods in the genus typically run in the hundreds; the fry are moved to a pit in the substrate after hatching and become free-swimming within a week or so, after which both parents continue to shepherd the school for another week or two. Raising fry is straightforward — newly free-swimming chanchitas take baby brine shrimp and microworms readily, and the parents generally do an efficient job of herding the school.
The most common mistakes with Australoheros in general — and sanguineus would be no exception — are housing a breeding pair in too small a tank without adequate cover for subordinate fish, and attempting to keep multiple adult males together. Water quality problems are rarely the issue: these are hardy, adaptable cichlids with a broad thermal and chemical tolerance, and they are undemanding feeders that accept most quality prepared foods alongside live or frozen invertebrates. A keeper who provides adequate space, sensible tankmates, and a clean, well-structured environment should find this an undemanding and rewarding fish — the blood-red caudal markings that give it its name are striking on a well-conditioned animal, and the parental behaviour is engaging to watch.
Conservation
The IUCN Red List assesses Australoheros sanguineus as Least Concern, in a global assessment carried out on 7 November 2018 by Brazil's Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and published in 2022 (reviewer P. Reis). The reasoning is that, although the species was described from just eleven specimens in a single small basin, more recent records in southern Santa Catarina indicate a wider state-wide distribution, and the known threats — while real — are not at present judged severe enough to endanger the population. Those threats are concrete: a substantial part of the rio Cubatão basin lies within a densely settled, rapidly urbanising region around Joinville, exposing the fish to the habitat degradation, channel modification and pollution that accompany urban growth in the coastal Atlantic forest. That backdrop matters, because the Atlantic forest is one of the most heavily cleared biomes on Earth — well under a tenth of its original cover survives — and the small, isolated coastal basins that hold endemics like this one are exactly the habitats most exposed to deforestation, urban sprawl and water-quality decline. On the positive side, the species' range overlaps protected areas, including the Área de Proteção Ambiental Serra Dona Francisca and the APA da Baleia Franca. The assessors flag no commercial or subsistence use, and call for basic work on the species' distribution limits, population trends and biology — a reminder of how little is yet known about a fish that has been formally named for barely a decade.