Taxonomy & naming
The species was described by the American ichthyologist Robert Rush Miller in 1974 as Cichlasoma regani, in a paper in the Proceedings of the Biological Society of Washington titled 'Cichlasoma regani, a new species of cichlid fish from the Río Coatzacoalcos basin, México.' The holotype (UMMZ 184756, in the University of Michigan Museum of Zoology) came from the Río Almoloya where it is crossed by the Trans-Isthmian Highway, about 21 mi north of the road's southern terminus, in northeastern Oaxaca — a small tributary feeding the larger Coatzacoalcos drainage. Like most New-World cichlids of its era, the fish spent decades parked in the vast wastebasket genus Cichlasoma. As that genus was dismantled it was shuffled first toward Vieja and Paraneetroplus, the deep-bodied 'mojarra' genera, but molecular work showed those groupings to be artificial. In 2015 McMahan, Matamoros, Piller and Chakrabarty (Zootaxa 3999) revised the herichthyine cichlids and erected the genus Maskaheros for regani and its close relative argentea; the comprehensive ddRAD and mitochondrial phylogeny of Říčan, Piálek, Dragová and Novák (2016) recovered the same lineage as a distinct evolutionary unit within the Middle American heroines. Maskaheros today is monotypic in everyday usage but holds two species, Maskaheros regani and Maskaheros argentea, both confined to the rivers of the Isthmus of Tehuantepec. The older combinations Vieja regani and Paraneetroplus regani are still seen in hobby and trade literature and remain valid synonyms of the same fish.
Morphology
Maskaheros regani is a large, tall, strongly laterally compressed cichlid built on the classic deep-bodied 'mojarra' plan of its genus. FishBase gives a maximum of 9 in standard length, which with the tail makes a fish of roughly a foot in total length; aquarists routinely report mature males somewhat larger, and old dominant males develop the heavy nuchal hump typical of the group. The body is silvery to pearly grey-green, frequently overlaid with iridescent blue-green flecking and a variable pattern of broken vertical bars on the flanks. The diagnostic feature — and the source of the genus name — is the set of broad, dark, mask-like bars that cross the head between and below the eyes; against the pale face these read almost like war-paint and immediately separate Maskaheros from the plainer-headed Vieja. Sexual dimorphism is modest and develops slowly: males grow larger, build the steeper forehead and nuchal hump, and may carry slightly more produced dorsal- and anal-fin tips, while ripe females are deeper-bellied and, in spawning condition, drop a visible ovipositor. Colour intensifies markedly in breeding adults. Keepers consistently note that the species is a notably slow grower, often lagging behind even the famously slow-growing congener Maskaheros argentea — a juvenile may take well over a year to reach a few inches.
Habitat
The species is endemic to the Atlantic (Gulf of Mexico) slope of southern Mexico, centred on the Río Coatzacoalcos basin in northeastern Oaxaca and eastern Veracruz, at the northern end of the Isthmus of Tehuantepec — the narrow neck of land where the Gulf and the Pacific come closest together. It is one of the cichlids that the Freshwater Ecoregions of the World project lists as endemic to the Coatzacoalcos ecoregion, a basin noted for a high proportion of strictly local fishes; the genus as a whole also reaches the small adjacent Tonalá drainage to the east. These are warm lowland-to-foothill rivers draining the Petén-Veracruz moist forest and the flanks of the Sierra Madre de Oaxaca, ranging from clear upland creeks to meandering coastal-plain rivers, side lagoons and backwaters. FishBase classes the fish as freshwater and benthopelagic and gives a preferred temperature band of roughly 75–79 °F; the trade and hobby experience broadly supports warm, near-neutral to mildly alkaline water (about pH 7.0–8.0) over the harder, more acidic extremes. Quantitative in-situ chemistry and a published depth range for this specific species are sparse, as is true for many narrowly-distributed Mexican cichlids; the figures here lean on FishBase's environmental envelope rather than a dedicated field-limnology study.
Feeding
Maskaheros regani sits low on the food web. FishBase records its diet as mainly vegetable bottom debris and aufwuchs — the carpet of algae, biofilm, detritus and associated micro-invertebrates that coats submerged rock and wood — and assigns it a trophic level near 2.0, the value expected of a committed herbivore-detritivore rather than a predator. This fits the genus: Maskaheros belongs to the lineage of deep-bodied Middle American cichlids that graze and browse low-energy plant and detrital food, and Říčan et al. (2016) note the genus expresses both the still-water (lentic) and flowing-water (lotic) body forms of its clade. In practice the fish works the substrate and hard surfaces, taking mouthfuls of sediment and aufwuchs and combing the bottom for what small animal life comes with it. Because so much of its energy comes from bulky, fibre-rich plant and detrital matter, it has the long gut and the patient, near-continuous feeding style of a grazer rather than the lunge-and-gulp habit of a piscivore — a distinction that matters in the aquarium, where an over-rich, protein-heavy diet does not suit it.
Mating
As with most large heroine cichlids, reproduction in Maskaheros regani is organised around a monogamous pair that forms a bond and then jointly holds a territory. Detailed field observations of courtship in this particular species have not been published, so the picture is assembled from the genus's biology and from aquarium reports. Pairs form within a group as fish mature, and pairing is best achieved by raising a cohort together and letting a bond develop rather than forcing two adults together. Courtship involves the usual cichlid repertoire of lateral displays, fin-spreading, jaw-locking and substrate cleaning, with both sexes intensifying in colour and the female dropping her ovipositor as she ripens; one aquarist documented a 9-inch female in full ovipositor display being 'gently attentive' to by a 12-inch male in the days before spawning. The species carries the reputation, shared with Maskaheros argentea, of being among the harder Central Americans to bring to a successful spawn — partly a function of its very slow growth, which makes it easy to lose fish before they ever mature, and partly the unpredictable intraspecific aggression that can flare as a pair claims and defends its patch.
Breeding
Maskaheros regani is a biparental substrate (open) spawner, the standard mode for its genus and for the deep-bodied Middle American cichlids generally. The pair selects and meticulously cleans a hard surface — a flat rock, a broad leaf, a slab of wood or, when nothing better is offered, the tank bottom — and the female lays an adhesive sheet of eggs over it while the male follows to fertilise. A precise wild clutch count has not been published for the species; large heroine cichlids of this body size typically lay on the order of several hundred eggs, and a productive pair can be expected to fall in that range. Both parents share the brood: the female fans and tends the eggs while the male patrols and defends the perimeter, and after the eggs hatch the wrigglers are moved to pre-dug pits before the free-swimming fry are shepherded as a tight school by both adults. The young feed initially on infusoria and fine prepared foods and, like the adults, grow slowly. Aquarium spawnings have been recorded but are not common; keepers report that early spawns from a young pair often fail before the pair settles into reliable parenthood, and that the fish may simply deposit eggs on the glass bottom rather than use a provided rock.
In the aquarium
Maskaheros regani is a fish for the experienced large-cichlid keeper rather than the beginner — not because it is delicate, but because of its eventual size, its slow maturation, and the management that large heroine cichlids demand. A foot-long, deep-bodied grazer needs real volume: a single adult or a pair is best in a tank of at least 75 US gallons (roughly 75 US gal), and a longer 100-gallon-plus footprint makes managing the fish, and any tankmates, considerably easier. The species is often described in the trade as relatively peaceful for its group, and outside of spawning it can be among the more manageable big Central Americans — but it is still a territorial cichlid that becomes markedly more aggressive in breeding condition, and pairs will claim and defend a substantial area. The most successful approach is to grow a group of six or more juveniles together, both to allow a natural pair to form and to spread aggression, accepting that you will need the space for several large fish along the way.
Water should be warm and stable, around 75–82 °F, with a near-neutral to mildly alkaline pH (about 7.0–8.0) and moderate hardness; the fish is hardy across this range but, like all big cichlids, is intolerant of accumulated dissolved waste, so generous filtration and large regular water changes are essential. A substrate of sand or fine gravel suits its bottom-grazing, sediment-mouthing habits; like its relatives it will rearrange décor and uproot rooted plants, so robust or potted plants, smooth water-worn rock, and driftwood that create broken sightlines and defensible territories are the sensible furnishings. Because the fish is naturally a herbivore-detritivore feeding on aufwuchs and plant debris, its diet should be built around quality vegetable- and spirulina-based prepared foods, supplemented sparingly with frozen or live items; an over-rich, meat-heavy diet is a poor match for its biology and is implicated in the bloat that plagues over-fed Central American grazers.
Tankmates should be similarly sized, robust cichlids and large, fast dither fish that can hold their own; very small or slow fish will be outcompeted or, during spawning, harassed. The two practical frustrations keepers report are the same two raised throughout: the fish grows agonisingly slowly, so patience is mandatory, and it is one of the harder Central Americans to spawn reliably, with young pairs often failing several times before they settle. Given space, clean warm water, a vegetable-leaning diet and time, it is a rewarding and strikingly marked aquarium fish; rushed or crowded, it disappoints.
Conservation
The IUCN Red List assesses Maskaheros regani as Data Deficient (DD), in an assessment by T.J. Lyons dated 29 November 2018. The Data Deficient listing reflects exactly what its biology suggests: a fish restricted to a single small Mexican basin for which there is not enough information on population size, trend or specific threats to place it confidently in a threatened or non-threatened category. It carries no CITES listing and is not evaluated under the CMS. That narrow, single-basin endemism is itself the heart of the conservation concern — a species confined to the Coatzacoalcos drainage (and the immediately adjacent Tonalá) has nowhere else to go, and the Coatzacoalcos basin is a heavily industrialised lowland region subject to the familiar pressures on Mexican Atlantic-slope rivers: habitat alteration, pollution, deforestation in the catchment, and introduced species. None of these is documented as a population-level threat to this particular cichlid, but for a Data Deficient single-basin endemic the appropriate posture is caution and a call for the basic distribution and population surveys the Red List flags as missing.