Taxonomy & naming
Heros sp. "Red Shoulders" is not a described species. It has no scientific name, no describing author, no year of publication, and no entry in Eschmeyer's Catalog of Fishes, because no taxonomist has published a description of it. It exists in the aquarium literature as an informal taxon, named in the standard convention for undescribed cichlids — the genus Heros, the abbreviation "sp.", and a trade name in quotation marks, here the English "Red Shoulders" (equivalent to the older German trade name Rotkeil, "red wedge," for the red shoulder blaze). It belongs unambiguously to Heros, the round, deep-bodied severum genus of the heroine cichlid radiation, and within that genus it is allied to the severus/efasciatus complex — the green, banded severums of the Amazon and Orinoco. Hobby specialists and several aquarium-trade references treat the Red Shoulder fish as either an undescribed Heros species or a distinct, geographically restricted colour population within that complex; it has been variously associated in the trade with Heros efasciatus and with the true Heros severus of the Rio Negro/Orinoco blackwaters. The honest position, pending a formal revision of the genus, is that this is a recognised severum-group form of the upper Rio Negro and Orinoco whose exact rank is unresolved, and that no authority or date should be attached to it. (Affinity to described severums is inferred from morphology and provenance; no invented authority should ever be applied.)
Morphology
In overall build this is a classic severum: a tall, strongly laterally compressed, almost disc-shaped cichlid, with the rounded outline and high dorsal and anal fins of the genus. Aquarium references put the maximum size in the region of 8–10 in total length, in line with other Heros of the severus/efasciatus group; most home-aquarium fish settle somewhat smaller. The diagnostic feature, and the source of every trade name, is colour. The ground is a greenish to silvery-gold, and across the shoulder and lower head a broad wash of orange to brick-red develops — strongest and most saturated in mature, well-conditioned males. The forehead and cheeks of males are typically dotted and vermiculated with dark spots and worm-lines; females tend to be paler, with the head markings reduced or absent. As in other severums, a series of dark vertical bars can flush across the flanks in display or stress, and a dark blotch sits near the caudal peduncle. Sexual dimorphism is the usual severum pattern: males grow larger, carry the more intense red and heavier facial vermiculation, and develop somewhat more extended dorsal- and anal-fin tips, while ripe females are rounder-bodied and plainer-headed.
Habitat
The Red Shoulder severum comes from the soft, acidic blackwater systems of the upper Rio Negro and the upper Orinoco, including the Casiquiare corridor that joins the two — the heartland of the true Heros severus and of several of the genus's most distinctive colour populations. Trade fish are typically exported from the Brazil–Colombia–Venezuela border region of the upper Rio Negro, around São Gabriel da Cachoeira and upstream. These are tannin-stained waters of very low conductivity and acidic pH, draining nutrient-poor white-sand (podzol) catchments, with submerged wood, leaf litter, and root tangles along the margins as the dominant structure. Like other severums, the fish is a quiet-water, structure-associated cichlid of the river margins, flooded forest, and slow side-channels rather than the open main channel or fast water. The genus as a whole spans the lowland Amazon and Orinoco basins; this particular form is tied specifically to the upper Negro/Orinoco blackwater province.
Feeding
Severums are omnivores with a strong herbivorous and frugivorous leaning, and the Red Shoulder form is no exception. In the wild, Heros of this group feed heavily on plant matter, fallen fruit and seeds, algae and detritus, supplemented by aquatic invertebrates and small benthic prey — the flooded-forest diet of a deep-bodied browser working the root tangles and leaf litter of blackwater margins. The genus sits at a relatively low trophic level for a cichlid, reflecting that vegetable bias. There is nothing predatory about its feeding; it is a generalist browser and picker rather than a hunter of other fishes. In captivity this translates directly into a need for a vegetable-forward diet, as described below.
Mating
Like all Heros, the Red Shoulder severum is a monogamous, biparental, pair-bonding cichlid. Pairs form out of a group as fish mature, and a bonded male and female select and clean a spawning site together, defending a territory around it. Courtship follows the standard severum repertoire of lateral displays, fin-spreading, jaw-locking trials of strength, and cooperative substrate-cleaning, with the male's intensified red shoulder and facial vermiculation serving as the principal nuptial signal. Outside of breeding the form is comparatively peaceable for its size, in keeping with the generally mild temperament of the severum group, though a spawning pair becomes territorial around the nest. As is typical of the genus, pairs are best allowed to self-select from a group rather than forced.
Breeding
The Red Shoulder severum is an open, biparental substrate spawner, in the standard Heros pattern. The adhesive eggs are laid in neat rows on a cleaned vertical or sloping hard surface — a flat stone, a broad leaf, a piece of driftwood, or the aquarium glass — and are tended by both parents, the female concentrating on fanning and direct egg-care and the male on territory defence, with the roles overlapping. After hatching the wrigglers are moved to pits and guarded; once free-swimming, the fry are herded and defended as a school by both parents, and severum fry are known to glean mucus from the parents' flanks in the early days, as in discus and other heroine cichlids. Clutch sizes in the severus/efasciatus group run to several hundred eggs in well-grown pairs. As with most heroine substrate-spawners, parental care is extended across eggs, larvae and free-swimming fry, and conditioned pairs will re-spawn at intervals. Soft, warm, acidic water of the kind the fish comes from favours fertilisation and egg development. (Specific wild clutch figures for this particular form are not separately published; the figures here are genus-typical and flagged as such.)
In the aquarium
The Red Shoulder severum is a well-established and popular ornamental, traded both as wild-caught upper-Rio-Negro fish and as captive-bred lines selected for intense red shoulders. It is among the more rewarding large-but-peaceful South American cichlids for a keeper who wants colour and presence without overt aggression.
Give it a tall tank with a generous footprint — on the order of 47 in length and a good volume for an adult or pair, more for a group — furnished to echo a blackwater margin: a soft sand substrate, plenty of driftwood and root structure, and tannin-stained, soft, warm, acidic to neutral water. Temperatures in the mid-to-high 20s Celsius (roughly 79–86 °F) and a pH on the soft, acidic side (around 5.0–7.0) match its origins; wild-caught fish in particular do best in soft, low-conductivity water, while tank-bred lines tolerate a wider range. Botanical leaf litter and good filtration with gentle flow round out the biotope.
Feed a vegetable-forward omnivore diet: a quality cichlid or herbivore pellet as the staple, generously supplemented with blanched greens, spirulina, and plant matter, plus periodic frozen or live invertebrates (bloodworm, brine shrimp) for protein. Severums are notorious for nibbling soft aquarium plants, so use tough or plastic plants if planting matters. For tankmates choose peaceful to moderate companions of similar size — other calm large characins, peaceful catfish, and mild cichlids — and avoid genuinely aggressive cichlids that will bully this mild fish, as well as anything small enough to be eaten. The common keeper mistakes are keeping it too cold, keeping wild fish in hard alkaline water, and pairing this gentle severum with belligerent tankmates.
Conservation
Heros sp. "Red Shoulders" has not been evaluated by the IUCN, and because it is an undescribed form without a formal scientific name it has no Red List assessment of any kind — no status, no category, no published criteria. As a member of the wide-ranging severum complex of the upper Rio Negro and Orinoco, it is not a narrow single-locality endemic, and the broader Heros severus/efasciatus group is common and widely traded. The general pressures on its blackwater home waters — deforestation, mining (including mercury contamination from gold extraction in the upper Negro and Orinoco), and the ornamental fishery itself — form the backdrop against which any future assessment would be read, but none is documented as a population-level threat to this particular form. No conservation status should ever be fabricated for it; the honest statement is that it is unassessed and, as part of a widespread complex, not currently considered at risk.