Taxonomy & naming
Dicrossus warzeli was described by Uwe Römer, Ingo J. Hahn and Pablo M. Vergara in 2010, in the journal Vertebrate Zoology, alongside its Rio Negro congener Dicrossus foirni. The two were the last of the five recognized checkerboard cichlids to receive formal names; warzeli had circulated in the hobby and the literature for nearly two decades under provisional labels including Dicrossus sp. "B" (Kullander, 1990), Crenicara or Dicrossus sp. "Tapajós" and sp. "Tapaios" (Warzel, 1996). The holotype, an adult male of 1.5 in standard length, is registered as MZUSP 106591 at the Museu de Zoologia da Universidade de São Paulo, with paratypes split between MZUSP and the Senckenberg collection in Dresden (MTD F). The description rested heavily on aquarium specimens and field observations supplied by Frank Warzel, who had collected the species himself. Within the genus, the authors diagnosed warzeli by its three longitudinal rows of horizontally elongate dash-like spots — a pattern unlike the clustered or double/triple vertical blotches of its relatives — and noted that warzeli and foirni appear to be more closely allied to one another than to the older species (maculatus, filamentosus, gladicauda), a hypothesis they flagged for genetic testing. Dicrossus belongs to the dwarf-cichlid radiation of the subfamily Cichlinae and is closely associated with the superficially similar genus Crenicara; both are commonly called checkerboard or chessboard cichlids.
Morphology
This is a small, slender, laterally compressed dwarf cichlid with pronounced sexual size dimorphism. Males are by far the larger sex, reaching about 2.5 in standard length (around 3 in including the tail in well-grown aquarium fish), while females stay markedly smaller at roughly 1.5 in SL; the IUCN account gives a mean standard length near 1.5 in. The diagnostic feature is the flank pattern: three longitudinal rows of dark grey to blackish, horizontally elongate, dash-like spots running along the body, giving the fish a far more linear, striped appearance than the blocky checkerboard of Dicrossus maculatus or filamentosus. As in other Dicrossus, this resting pattern can collapse into a single dark longitudinal band when the fish is aggressive or stressed. Mature males develop the genus's signature finnage — elongated, filamentous extensions of the anterior dorsal and ventral fin rays, light blue to metallic-green submarginal banding along the dorsal and the spade-shaped (lyre-tailed) caudal, and white-tipped ventral fins. Females are plainer and rounder-bodied, especially when ripe. The teeth are small and unicuspid, recurved, suited to picking small prey from the substrate.
Habitat
Dicrossus warzeli is endemic to Brazil, restricted to the middle and upper Rio Tapajós system on the northern slope of the Brazilian Shield — the FEOW Tapajós–Juruena freshwater ecoregion — with records concentrated in the state of Pará. The describers list collecting sites in small forest streams (igarapés) near São Luiz, the type locality, and the Igarapé Pimental, among others. The species has been found exclusively in clearwater rivers and their tributary brooks, never in black or white water. These are exceptionally soft, acidic habitats: field measurements recorded no detectable hardness and very high acidity, with pH regularly below 5 and most often below 4. The streams themselves are shallow, with sandy bottoms broken by patches of submerged leaf litter; juveniles of about 1 in SL were collected in exactly these small sandy brooks. Tapajós clearwater runs warm, broadly 79–86 °F in this part of the basin. The genus's overall biology in the wild remains thinly documented, and the original authors explicitly noted that intensive field research on the ecology of warzeli and foirni is still needed.
Feeding
Like its congeners, Dicrossus warzeli is a micro-predator and detritus-picker of the stream bottom. Frank Warzel observed wild juveniles searching the substrate for small invertebrates and detritus, actively picking up and turning over submerged leaves to expose prey beneath them — a foraging style well suited to the leaf-littered sandy brooks it inhabits. Its small, recurved unicuspid teeth fit this diet of tiny benthic animals rather than the algae-rasping or hard-shelled fare of larger cichlids. In the leaf-litter community of a Tapajós headwater it functions as one of the small, low-level invertebrate feeders, taking aquatic insect larvae, micro-crustaceans and the associated organic film.
Mating
Dicrossus are open substrate spawners with female-centred brood care, and warzeli follows the genus pattern. Pairs are not strongly bonded; courtship and territory revolve around the female, who establishes and defends a small spawning site, while the male's role is comparatively peripheral. Keepers and the Aquarium Glaser breeding account both note that the female can be markedly dominant toward the male, and that males display vigorously — the same fish that drops its checkerboard pattern for a dark stripe when sparring (a male was filmed fighting its own mirror image). As with the closely related Apistogramma and the other checkerboards, a soft, warm, humic-stained environment and the presence of suitable flat or sheltered spawning surfaces are what bring fish into breeding condition; aggression in confined quarters is the main social hazard.
Breeding
Unlike the cave-spawning Apistogramma, Dicrossus are open spawners that deposit eggs on an exposed surface — a leaf, a stone, or a piece of wood — rather than inside a cavity. Brood care is primarily maternal: the female tends and defends the clutch and, after hatching, the wrigglers and free-swimming fry, while the male guards the wider territory. Clutch sizes are not precisely documented for warzeli, but congeneric checkerboards typically lay small clutches on the order of a few dozen to roughly a hundred eggs, consistent with a fish of this size. Captive breeding is notoriously difficult and was for years considered the species' great unsolved challenge. Frank Warzel succeeded in spawning his wild fish in the 1990s but could not raise the young; commercial tank-bred fish only began to appear much later, after careful attention to very soft, acidic, humic water. The extreme water chemistry of the wild habitat — pH often below 4 and essentially zero hardness — appears central to fertilization and fry survival, and replicating it is the principal obstacle to breeding the species in numbers.
In the aquarium
Dicrossus warzeli is one of the most sought-after and least available dwarf cichlids in the hobby; commercial imports have always been sporadic, and even specialist suppliers report handling it only a handful of times. It is a fish for the experienced soft-water aquarist, not a beginner's cichlid, and its demands are exacting. A pair can be housed in a modest footprint — a tank of roughly 23.5–31.5 in length (about 20 US gal) suffices for a single pair — but the water must be right: warm (about 79–86 °F), very soft, and distinctly acidic. Keepers target soft water with a pH well below 7, and breeding attempts push toward the markedly acidic conditions of the wild habitat, achieved with reverse-osmosis water re-mineralized minimally and heavily conditioned with humic substances. Alder cones, dried leaf litter (such as oak or beech) and peat-stained blackwater are repeatedly emphasized as important, both for the tannins they release and for the microfauna and biofilm the decaying leaves support. A fine sand substrate with scattered leaves and driftwood reproduces the stream floor the fish forages over, and subdued lighting suits it.
Water quality must be impeccable and stable; like many extreme soft-water specialists this species does not tolerate dissolved-waste accumulation or sudden parameter swings. Gentle filtration and current are appropriate for a fish of quiet forest brooks. Tankmates should be small, peaceful soft-water companions — pencilfish, small tetras and similar characins of the same biotope — and the species is best kept as a single pair or in a group only in a larger, well-structured tank, since females in particular can be dominant and aggression flares in cramped quarters. Diet is straightforward for a micro-predator: small live and frozen foods such as cyclops, daphnia, baby brine shrimp, micro-worm and finely chopped bloodworm are taken eagerly and bring out the best colour and condition; dry foods are accepted less reliably. The two real difficulties are simply obtaining the fish and supplying — and holding steady — the very soft, acidic water it needs to thrive and, especially, to breed.
Conservation
The IUCN Red List assesses Dicrossus warzeli as Least Concern (assessed 2018 by the Instituto Chico Mendes de Conservação da Biodiversidade, ICMBio, Brazil's federal conservation agency). The assessment notes that the species is naturally infrequent and of low abundance, and that it is endemic to the middle and upper Rio Tapajós in the state of Pará. The principal flagged pressure is the suite of proposed hydroelectric dams on the middle and upper Tapajós, which would substantially alter the river; however, because warzeli lives predominantly in small forest igarapés rather than the main channel, the assessors judged that those impacts are unlikely to constitute a significant threat to the species itself. It carries no CITES listing. Beyond dams, the wider Tapajós basin faces the familiar Amazonian pressures of deforestation and gold-mining, and the species' narrow range and specialized clearwater, soft-acid habitat mean its long-term status is best read against the health of those headwater streams rather than treated as secure indefinitely.