Taxonomy & naming
The chocolate cichlid was described by the German-British ichthyologist Albert Günther in 1862, in the fourth volume of his Catalogue of the Fishes in the British Museum, as Heros temporalis. The description was based on a single specimen of Brazilian origin with no more precise locality recorded; that fish, register BMNH 1855.12.26.638 (received from the Zoological Society), survives as the unique holotype. Like many names of its era the binomial then drifted through a succession of catch-all genera. For much of the twentieth century the fish and its relatives were lumped into the vast wastebasket genus Cichlasoma, and the so-called 'chocolate cichlids' accumulated a tangle of competing names in the hobby literature — goeldii, crassa, hellabrunni among them — that made identification a genuine headache. The Swedish ichthyologist Sven O. Kullander resolved the muddle in his 1986 monograph on the cichlids of the Peruvian Amazon, erecting the new genus Hypselecara for the group and recognizing just two valid species: Hypselecara temporalis and the more elongate Hypselecara coryphaenoides (Heckel, 1840). Kullander placed goeldii, crassa and hellabrunni in the synonymy of temporalis, and niger, arnoldi and axelrodi in that of coryphaenoides. The fish had briefly been treated as Cichlasoma temporale by Ortega and Vari (1986) before Kullander's generic split took hold; the current combination, Hypselecara temporalis, has been stable and uncontested in the modern checklists (Kullander in Reis et al. 2003; Meza-Vargas et al. 2021) ever since. The genus sits in the subfamily Cichlinae, among the large-bodied Neotropical heroine cichlids.
Morphology
Hypselecara temporalis is a deep-bodied, strongly laterally compressed cichlid whose overall silhouette is almost circular — a steeply rising, slightly convex forehead and a tall disc of a body that recalls a heavy-built severum or a small uaru. It is this elevated head profile that gives the genus its name. Reported size varies with how it is measured: FishBase lists a maximum of about 6.5 in standard length, a common length around 8.5 in total length, and a maximum reported length of roughly 12 in TL, and well-grown aquarium fish do reach ten to twelve inches. Mature males develop a pronounced nuchal (frontal) hump and tend to grow larger, with somewhat more produced dorsal and anal fins; females stay a little smaller and keep a smoother head — the hump is the single most useful sexing cue once the fish are adult. The species' signature is its remarkable, fast colour change. The ground colour can swing within minutes between chocolate-brown, olive, golden-yellow, reddish and a striking emerald or sea-green, driven by mood, social context, light and breeding state — a flat brown fish in the morning may be glowing green by afternoon. Against that shifting background two dark markings are usually visible: a blotch on the mid-flank and a second dark mark on the upper part of the gill cover, behind and below the eye. The reddish-orange eye stands out against whatever colour the body happens to be wearing. Juveniles are comparatively drab — olive-brown with dark barring — and the full colour-shifting repertoire develops only as the fish matures past about 4 in.
Habitat
The chocolate cichlid is broadly distributed through the lowland Amazon basin. FishBase and the Catalog of Fishes record it from the Ucayali and Amazon drainages of Peru, the Amazonas (Amazon) drainage of Colombia, and the Solimões–Amazon mainstem of Brazil eastward to Cametá near the river mouth, together with rivers of Amapá and the Oyapock (Oiapoque) basin on the Brazil–French Guiana border; Ecuador is included in the IUCN range. This is a fish of slow-moving, often turbid waters rather than clear or strongly blackwater habitats. In the wild it favours sluggish river margins, floodplain lakes, backwaters and flooded forest over muddy and sandy bottoms, using fallen timber, root tangles and submerged structure as cover and as territory markers. Its preferred water is warm and chemically forgiving: FishBase gives a pH range of about 5.0–7.5, a hardness range from very soft (around 0.3 dH) up to roughly 20 dH, and temperatures of about 77–86 °F — soft and acidic to near-neutral, but tolerant of a wide envelope, which is part of why the species adapts so readily to tap water in captivity. As a benthopelagic floodplain fish it occupies the shallow, seasonally inundated waters of the basin; no firm maximum depth has been published, and it is most associated with the upper few metres of slow lowland channels and lagoons. Seasonal flood-pulse expansion and contraction of habitat, and the gradual chemical shifts that accompany it, are the normal backdrop of its life.
Feeding
Hypselecara temporalis is an opportunistic omnivore that forages low in the water column over soft bottoms and around submerged wood. FishBase places it at a low trophic level of about 2.4, consistent with a diet weighted toward small invertebrates, aquatic insect larvae, algae, detritus and plant material gleaned from the substrate and the surfaces of flooded timber. Its broad, deep body and unspecialised dentition suit a generalist that takes whatever the floodplain offers rather than a dietary specialist; in captivity this translates into a famously unfussy feeder that accepts almost anything. Vegetable matter appears to be a genuine part of the natural diet, not an afterthought, and the species does best on a mix of animal and plant foods. In the lowland community it functions as a mid-to-large generalist of the slow, turbid backwaters, neither a dedicated piscivore nor a substrate-sifting eartheater, but a deliberate, broadly foraging omnivore.
Mating
Chocolate cichlids are gregarious and relatively peaceful outside of reproduction, but pair formation reorganises their behaviour around a defended territory. They are not reliably sexed as juveniles, so keepers typically grow out a group of six or so and let pairs sort themselves out naturally — a slow, self-selecting process that is the usual route to a stable, compatible bond. Once a pair forms it tends to be durable, and both partners take an active role: a ready pair intensifies dramatically in colour, with the two fish often showing their most vivid emerald, gold and red tones simultaneously as they court. They clean a chosen spawning surface together, circle one another, and jointly defend the area around it. For a fish of its size the species is strikingly restrained — it will squabble with large tankmates over prime real estate and will defend a brood vigorously, but it lacks the relentless aggression of an oscar or a green terror. The main difficulty in breeding it is social rather than environmental: getting two fish that genuinely accept one another, after which the pair bond and the shared territorial defence fall into place readily.
Breeding
Hypselecara temporalis is a biparental substrate spawner with attentive shared brood care. FishBase notes that spawning occurs in holes dug in the substrate and that both parents watch over the eggs and alevins, and mature males are flagged by their well-developed frontal hump. In practice the pair cleans a firm vertical or sloping surface — a flat rock, a slab of slate, or a smooth piece of driftwood — onto which the female lays neat rows of adhesive eggs that the male then fertilises. Reported clutch sizes are large and scale with the female, commonly cited in the range of roughly 200–600 eggs. Both parents guard and fan the clutch and pick off any eggs that fungus over; the eggs hatch in about three to four days, after which the wrigglers are moved into shallow pits excavated in the sand and become free-swimming roughly five to seven days post-hatch. The free-swimming fry are herded, led around the tank and aggressively defended by both parents, who may remain attentive for several weeks to a month or more. First foods are the usual small fare — newly hatched brine shrimp, microworms and finely powdered prepared food. A modest, slightly cooler water change, soft and warm conditions (around pH 6.0–6.5 and 81–84 °F), and conditioning on rich live and frozen foods are the standard triggers; the fry themselves are not difficult to raise once a compatible pair commits.
In the aquarium
The chocolate cichlid has a long history in the hobby and is frequently held up as one of the best large cichlids for a community of medium-to-large South Americans — but it asks for real space and a long-term commitment, and it is routinely under-housed. Adults reach ten to twelve inches and live ten to fifteen years, so plan for the adult, not the four-inch juvenile in the dealer's tank. A single adult wants a 75-US-gallon (about 280-litre) tank as an absolute floor; a pair, or a pair with community fish, is far better served by 125 gallons (around 125 US gal) or more, both for swimming room and for the sight-line breaks that keep a large cichlid calm. The most common ways keepers lose or spoil these fish are chronic under-stocking of tank size — a stunted chocolate cichlid is a stressed, dull-brown shadow of a healthy one — and neglected water quality, which, as with most big heroine cichlids, invites head-and-lateral-line erosion (hole-in-the-head).
Give them a mature, well-filtered tank with a strong canister or sump turning over the volume several times an hour, but keep the flow moderate: these are fish of slow, turbid floodplain water, not fast rivers, and a stiff current across the whole tank stresses them. Weekly water changes of a quarter to a third of the volume are not optional for a fish of this bioload. A sand or fine-gravel substrate matters, because spawning pairs excavate pits and will rearrange the bottom; coarse, sharp gravel is unkind to a digging fish. Furnish with substantial driftwood and smooth boulders for cover and sight-breaks, and add a flat rock or vertical slate or two if breeding is the goal. Planted aquascapes and chocolate cichlids have an uneasy relationship — plants anchored to wood or rock (anubias, java fern, bolbitis) survive, but rooted plants are at risk, especially around spawning.
Water chemistry is one of the species' easier aspects: its broad tolerance (pH roughly 5.0–7.5, soft to moderately hard) accommodates most tap water without RO or elaborate softening, though soft, slightly acidic water and warm temperatures (about 75–84 °F, the upper part of the range preferred) bring out the best colour and the readiness to breed. Consistency matters more than hitting a precise target; avoid sharp swings. Feeding is undemanding — a quality cichlid pellet as the base, supplemented with frozen krill, mysis, bloodworm and brine shrimp, and genuine vegetable matter (spirulina foods, blanched zucchini, spinach, peas), which this omnivore needs for proper health and colour. They will happily overeat, so portion accordingly.
On compatibility, the chocolate cichlid earns its 'gentle giant' reputation: it coexists with severums, peaceful Geophagus eartheaters, uaru, large peaceful tetras and silver dollars, and mid-to-large plecos and catfish far more gracefully than most cichlids its size. Two cautions apply. Anything small enough to fit in its mouth is food, so keep tankmates to a sensible minimum size; and genuinely aggressive cichlids — red devils, jaguars and the like — will simply dominate this retiring fish. A breeding pair will, predictably, hold and defend a territory, but even then the aggression is moderate by big-cichlid standards. Watch the colour: a healthy chocolate cichlid changes shade constantly, and a fish locked into flat dark brown is telling you something is wrong before any other symptom appears.
Conservation
The IUCN Red List assesses Hypselecara temporalis as Least Concern (assessed 19 November 2020 by R.G. Frederico, published 2023), citing a very wide distribution across the Amazon basin spanning Brazil, Colombia, Ecuador and Peru, and a population judged to be stable. It carries no CITES listing and is rated harmless to humans. The species supports a minor commercial food fishery and a steady ornamental trade — it is sold both as the 'chocolate' and the 'emerald' cichlid, and occasionally still under the old name Cichlasoma temporale — but neither is flagged as a population-level threat, and FishBase scores its intrinsic fishing vulnerability as low with a high resilience (a population doubling time under fifteen months). As a widely distributed, chemically tolerant habitat generalist, it is far less exposed than the basin's many narrow-range endemics. The broader pressures on Amazonian freshwaters — dam construction, deforestation, mining and altered flood-pulse regimes — form the backdrop against which any Amazon species should be read, but none is documented as a present danger to this adaptable and abundant cichlid.