Taxonomy & naming
Cichla kelberi was described by Swedish ichthyologist Sven O. Kullander and Brazilian colleague Efrem J. G. Ferreira in their 2006 revision of the genus Cichla (Ichthyological Exploration of Freshwaters 17(4):289–398), the monograph that lifted the recognized peacock basses from a handful of confused names to fifteen species and added nine new ones in a single stroke. The holotype (MZUSP 92397, in the Museu de Zoologia da Universidade de São Paulo) came from Tucuruí, on the lower Tocantins in Pará, Brazil, with 52 paratypes split between MZUSP and the Swedish Museum of Natural History (NRM).
The genus name Cichla is an old Greek word (kichle) for a wrasse, recycled by early naturalists for these chunky predators; the species honors Dieter Kelber, a German recreational angler who promoted Cichla as sportfishes and supplied Kullander and Ferreira with information and images of peacock basses. The fish sits in the Neotropical subfamily Cichlinae, family Cichlidae. Its status is not entirely settled: Eschmeyer's Catalog of Fishes lists it as valid as Cichla kelberi, and most recent Brazilian checklists agree, but a minority of workers (Willis et al. 2012; Sabaj et al. 2020) have folded it into the older, broadly defined Cichla ocellaris Bloch & Schneider, 1801. We follow the Catalog of Fishes and the bulk of the post-2017 literature in treating kelberi as a distinct species.
Morphology
This is a classic peacock-bass shape — fusiform, deep-bodied, big-mouthed — built for short, explosive pursuit. FishBase records a maximum of 23 in standard length and 4.9 kg (10.8 lb), though most fish encountered are well under that.
Kullander and Ferreira's diagnosis is the cleanest way to separate it from its near-twins. Adult Cichla kelberi carry small light (often yellowish) spots on the pelvic and anal fins and on the lower lobe of the caudal fin — the feature hobbyists fixate on and the reason the fish is sold as the "yellow" peacock bass. Like its close relatives Cichla monoculus and Cichla pleiozona, it shows three dark vertical bars on the flank, a pronounced occipital bar that strengthens with age, no black or ocellated markings on the head, and irregular dark blotches along the front of the belly. It is told from Cichla pleiozona by having fewer scales in a lateral row (76–83 versus 84–93) and by typically lacking a fourth bar. As in most Cichla, breeding and dominant fish intensify in color, and large males develop the nuchal hump typical of the genus.
Habitat
Cichla kelberi is native to the Araguaia and lower Tocantins river drainages of eastern Brazil — the FEOW Lower Tocantins–Araguaia freshwater ecoregion. That system drains north into the Atlantic and is often treated as part of the greater Amazonian fauna, even though it is geographically a basin adjacent to the Amazon proper — a distinction worth keeping straight, because much of what people call this fish's "Amazon" range is actually introduced.
Within its native rivers it favors lentic and slow water: lagoons, backwaters, and the still margins of channels, where clear water lets a sight-hunting predator work. FishBase classifies the species as benthopelagic and freshwater, in the tropical band; no species-specific depth range has been published. The genus as a whole is strongly associated with transparent and clear-to-blackwater conditions rather than heavily silted whitewater, and field studies of Cichla consistently tie feeding success to water clarity. Beyond its homeland, kelberi has been stocked or has escaped into reservoir after reservoir across southeastern Brazil (the upper Paraná basin, the Rio Grande and Paranaíba systems), into the Pantanal, and even — as a single documented specimen — into Lake Kinneret in Israel. Reservoirs suit it: warm, clear, structurally simple lakes with no co-evolved predators are close to ideal.
Feeding
Cichla kelberi is an apex-level, diurnal, sight-feeding piscivore — FishBase places it at trophic level 4.4. A 2011 study of its digestive-tract morphology in an oligotrophic Brazilian reservoir (dos Santos, dos Santos & Araújo 2011) confirmed the short gut and other features expected of a dedicated fish-eater. Adults take mostly fish; smaller individuals broaden the diet with insects and microcrustaceans before converting fully to piscivory as they grow.
Its ecological signature is what makes it notorious. In Brazilian reservoirs the species frequently preys heavily on introduced tilapia and on small native characins and other cichlids, and cannibalism on its own juveniles is well documented in the genus. Because these are diurnal, visually oriented hunters, they thrive in the clear, still water that impoundments create — and because the reservoirs they invade usually hold no fish capable of eating an adult peacock bass, the species sits at the top of a simplified food web with little to check it.
Mating
Like all Cichla, kelberi is a substrate-spawning, biparental cichlid rather than a mouthbrooder, and pair formation precedes any spawning. Ahead of breeding, mature fish pair off and establish a defended patch of shallow, often muddy-bottomed shoreline in standing water; in introduced populations this courtship season runs long, with Gomiero and co-workers (2009) documenting a prolonged spawning period through spring and summer in a São Paulo lake. The pair excavates a nest at this site before spawning externally. In novel habitats without predators or competitors, these fish mature small — first maturity at roughly 7.5–9.5 in in the São Paulo study, near 8–8.5 in in the reservoir Souza et al. (2008) examined, and FishBase records a length at first maturity of about 8 in — and they pair and breed continuously, sometimes showing a kind of stunting (nanism) under crowding, which is precisely the combination that drives population explosions.
Breeding
Once the pair has spawned over its cleaned substrate, both parents guard the clutch intensively: in the typical division of labor the female tends the eggs and larvae while the male patrols the territory and drives off intruders, and the parents continue to shepherd the resulting school of free-swimming fry. The young require abundant zooplankton, which is part of why the genus prefers lentic environments for breeding. Reproductive studies of introduced populations paint a picture of a fast, flexible breeder: Gomiero et al. (2009) found parceled (batch) spawning, with mean fecundity around 12,000 oocytes and batches near 4,900. In reservoirs without predators or competitors the species breeds repeatedly through the warm season, and the combination of guarded fry schools and continuous batch spawning lets a founding population build quickly — the reproductive engine behind kelberi's success as an invader.
In the aquarium
Peacock bass are sold small and stunning, and that is the trap. Cichla kelberi is among the smaller members of the genus, but "smaller" still means a large predator that pushes 18–20 in (17.5–19.5 in) and carries a heavy bioload. Experienced keepers on cichlid-forum.com and MonsterFishKeepers are blunt: an 8-foot tank is not enough, with a 10-foot (3-meter) tank roughly 36 in wide treated as a practical minimum, and an indoor pond better still. Care-sheet figures of "180 gallons" describe a grow-out, not a permanent home.
The harder problem is water quality. Multiple long-time keepers report that these fish are intolerant of hard, alkaline water and especially of nitrate, with anecdotal targets of pH near 6.0 and nitrate kept below about 5 ppm through aggressive water changes; neglect that and they slide into hole-in-the-head, fin and skin problems, and slow decline. Temperament is the final surprise: a fearsome predator to anything bite-sized, kelberi is often a coward among other large cichlids and can be bullied by far smaller, scrappier tankmates. The honest verdict is that this is not a beginner fish and not really a glass-aquarium fish at all — it is a specialist's project that rewards huge water volume, pristine chemistry, and restraint in stocking.
Conservation
On its own account Cichla kelberi is secure: the IUCN Red List assesses it as Least Concern (assessed 7 November 2018, by the Instituto Chico Mendes de Conservação da Biodiversidade, ICMBio), it is not listed by CITES, and within its native Araguaia–Tocantins range it is a common, widely distributed fish that also supports valued sport and food fisheries (the "tucunaré amarela"). There is no evidence of population collapse in its homeland; the pressures it faces there are the general ones bearing on Neotropical rivers — damming, deforestation, and changing flow — rather than targeted overexploitation.
The more important conservation story runs the other way. Across the wider Amazonian and Paraná basins — whose freshwater fish diversity is catalogued in works such as Kullander's treatment in the Check List of the Freshwater Fishes of South and Central America (Reis, Kullander & Ferraris, 2003) and described by Lowe-McConnell's classic ecological studies — most native cichlids are Least Concern or simply unevaluated, and the headline threats are habitat change and the ornamental and sport-fish trades rather than wholesale collapse. Cichla kelberi is itself one of those threats. Pelicice and Agostinho (2009, Biological Invasions 11:1789–1801) documented the destruction of a reservoir's fish assemblage after kelberi was introduced, and a broader literature on introduced Cichla treats the genus as an emerging menace to Neotropical and tropical fish communities worldwide. So the accurate framing is two-sided: the species is in no danger, but the basins it has been carried into are under real strain, and kelberi is frequently part of the strain rather than a victim of it.