Taxonomy & naming
Chromidotilapia regani was described by the French ichthyologist Jacques Pellegrin in 1906, originally as Pelmatochromis regani, from material collected in Gabon. The species was later transferred to Chromidotilapia, the genus George Albert Boulenger had erected in 1898 with Chromidotilapia kingsleyae as its type species by monotypy. The genus belongs to the African cichlid subfamily Pseudocrenilabrinae and is the type genus of the chromidotilapiine lineage, a West and Central African radiation that represents one of the oldest surviving branches of the African cichlid tree. Within Chromidotilapia, the genus today holds roughly a dozen valid species spread from Liberia to the Congo, with Gabon as its centre of diversity. The most authoritative modern treatment of Chromidotilapia regani is Anton Lamboj's redescription, 'Chromidotilapia (Teleostei: Cichlidae) in Gabon, with a redescription of Chromidotilapia regani (Pellegrin, 1906)' (Verhandlungen der Gesellschaft für Ichthyologie, Band 3, 2002), part of the same body of work in which he described several of the species' Gabonese neighbours (Chromidotilapia mrac, Chromidotilapia mamonekenei, Chromidotilapia elongata, Chromidotilapia nana and Chromidotilapia melaniae). Lamboj found that Chromidotilapia regani has no especially close relative among the other Gabonese Chromidotilapia; its high gill-raker count and pigmentation pattern instead suggest an affinity with the wide-ranging Chromidotilapia guntheri of West Africa. The species also features in his comprehensive reference 'The Cichlid Fishes of Western Africa' (2004).
Morphology
Chromidotilapia regani is a small, fusiform cichlid reaching about 5 in in standard length, with the elongate, gently arched profile typical of the genus. The fin counts run to 14–17 dorsal spines and 10–12 soft rays, with three anal spines and 6–8 anal soft rays. Its single most useful diagnostic feature is internal: the first outer branchial arch carries an unusually high number of gill rakers — between roughly 23 and 31 — markedly more than its Gabonese congeners, a count that reflects the species' detritus- and aufwuchs-based diet. A second diagnostic trait lies in the dorsal fin, where the first spine measures only 70–80 percent of the length of the fifth. In life the fish is an understated brassy-olive to greyish-brown, lit on the flanks and unpaired fins with the metallic flecking the genus is named for. The clearest field mark appears under stress or in confrontation, when two continuous dark longitudinal bands run the length of the body. Sexual dimorphism in Chromidotilapia is real but subtle: as in its relatives, the female is the more colourful sex, developing a brighter belly or ventral flush in breeding condition, while males tend to grow slightly larger and to carry marginally more extended unpaired fins. The sexes are otherwise similar enough that confident pairing usually depends on watching behaviour rather than on a single external character.
Habitat
The species is endemic to Gabon, where it occupies the northern part of the Ogowe (Ogooué) river system and the smaller coastal drainages of the country's northwest, north of Libreville. The Ogowe is the dominant river of Gabon, travelling some 1,124 mi in a great forested arc from headwaters in the Republic of the Congo to the Atlantic; Chromidotilapia regani is a fish of its middle and lower forested reaches rather than its headwaters. It lives in medium-sized and large rivers, and shows a clear ontogenetic shift in where it is found: small specimens keep to shallow marginal water, occurring singly or in small groups of two to four among sunken wood and stones close to the bank, while adults move out into deeper water toward midstream. These are the soft, warm, often tea-stained forest waters characteristic of the Lower Guinean rainforest belt — low in dissolved minerals, mildly acidic to near-neutral, and warm year-round. Published in-situ chemistry specific to this species is sparse, but Gabonese Chromidotilapia habitats are consistently reported as soft and acidic to circumneutral with water temperatures in the middle-to-upper twenties Celsius, and the species is treated as a lowland-forest river fish throughout its restricted range.
Feeding
Chromidotilapia regani is a benthic omnivore that leans heavily toward plant and detrital material. Its diet is reported to consist mostly of detritus, aufwuchs (the film of algae, micro-organisms and associated tiny invertebrates that coats submerged surfaces) and other preferably vegetative components, gathered from the bottom and from sunken wood and stones along the banks. The genus as a whole is benthophagous — sediment-sifting feeders that take mouthfuls of substrate and detritus and sort the edible fraction — and the elevated gill-raker count that diagnoses Chromidotilapia regani is consistent with this fine-particle, micro-feeding habit. FishBase places it at a trophic level near 3.4, reflecting a mixed diet in which small invertebrates supplement the dominant vegetable and detrital intake. In its riverine community it functions as a low-level forager working the leaf litter, biofilm and soft sediment of the river margins and bed.
Mating
Reproduction is where Chromidotilapia is most remarkable, and Chromidotilapia regani follows the genus pattern: it is a monogamous pair-bonder. Rather than the harem or lek systems common among African cichlids, a single male and female form a lasting bond and together defend a shared territory. Courtship is mutual and drawn out, with the more brightly coloured female playing a conspicuous role in pair formation and in signalling readiness to the male. Once bonded, both partners hold and defend the spawning site against intruders. Because the bond is between two individuals of broadly similar size and temperament, pairing in confinement can be fraught — an unwilling or mismatched partner may be harried — but an established pair is cooperative and comparatively peaceful by cichlid standards, directing its aggression outward at the territory boundary rather than at each other. This monogamous, jointly territorial social structure is the behavioural foundation for the shared mouthbrooding that follows.
Breeding
Chromidotilapia is one of the very few African cichlid genera to practise biparental ovophile mouthbrooding, and Chromidotilapia regani breeds in this fashion. The pair first spawns onto a cleaned firm surface — a stone, root or pit — in the manner of a substrate spawner, the female laying a row of eggs and the male following to fertilise them. The eggs are then taken up into the mouth and carried, with both parents sharing the brooding duty rather than the female alone; in this genus the female typically takes the larger share of incubation while both partners guard the brood and may exchange or co-hold the developing young. Clutches are modest, as befits a mouthbrooder that invests heavily per egg: congeners commonly produce broods on the order of a few dozen to perhaps sixty or so comparatively large eggs, far fewer than an open substrate-spawning cichlid of similar size would lay. After the larvae hatch and absorb their yolk, the free-swimming fry continue to shelter in the parents' mouths, bolting back inside at any threat, and the pair guards the school for an extended period after release. Specific wild fecundity figures for Chromidotilapia regani itself have not been published, so clutch size here is given as genus-typical; the essential and well-documented facts are the monogamous pair bond and the shared, biparental carrying of eggs and young.
In the aquarium
Chromidotilapia regani is a specialist's fish rather than a common import — most aquarium experience with the genus comes from Chromidotilapia guntheri and Chromidotilapia kingsleyae — but its requirements follow the well-understood pattern for these West-Central African pair-bonding mouthbrooders, and field collectors in Gabon routinely find it alongside Chromidotilapia kingsleyae and Parananochromis. A single pair is best kept in a tank with a base footprint of around 120 by 17.5 in or larger; the species is not large, but the pair needs floor space to hold a territory and, crucially, room for a prospective partner to retreat during the tense business of pairing. The most reliable way to obtain a pair is to grow on a group of six or more juveniles and let a bond form, then remove surplus fish, because forcing two adults together can end badly. Water should mirror the soft, warm forest rivers of the Ogowe: a temperature in the mid-twenties Celsius (roughly 75–81 °F), a pH on the acidic-to-neutral side (around 6.0–7.5), and low to moderate hardness. The species is sensitive to deteriorating water and benefits from generous filtration kept at a gentle flow, together with regular partial water changes. Furnish the tank as a structured riverbank: a soft sand bottom over which it can sift detritus, plenty of bogwood and rounded stones to break up sightlines and define a territory, and shaded, subdued lighting. Diet is undemanding — a varied menu of quality sinking pellets and frozen or live foods such as bloodworm and small crustaceans, supplemented with vegetable matter or a spirulina-based food to suit its largely herbivorous, detritus-feeding nature. Outside of breeding the species is relatively peaceful and suits a community of robust but non-aggressive West-African or other soft-water fishes that will not outcompete it at the bottom; the chief management challenge is intraspecific, around forming and maintaining the pair. Because true Chromidotilapia regani is rarely traded and is easily confused with its Gabonese relatives, sourcing correctly identified stock is itself part of the difficulty.
Conservation
The IUCN Red List assesses Chromidotilapia regani as Vulnerable under criterion B2ab(iii) (assessed 16 February 2009 by T. Moelants, published 2010), with the population trend listed as unknown. The assessment reflects the species' genuinely restricted range — it is endemic to the northern Ogowe system and a few coastal drainages of northwestern Gabon — combined with a continuing decline in the extent and quality of its forest-river habitat, the basis of the B2ab(iii) listing. The fish is of no fisheries interest and carries no CITES or CMS listing, so direct exploitation is not the concern; rather, the threat is habitat-driven, as logging, land-use change and other pressures degrade the lowland rainforest streams of Gabon on which a narrow-range endemic like this depends. Gabon retains some of the best-preserved freshwater habitat in Central Africa, which works in the species' favour, but its small global distribution leaves it with little margin, and the Vulnerable rating should be read as a flag that its range is too confined for any widespread habitat loss to be absorbed safely.