Taxonomy & naming
Enigmatochromis is a monotypic genus erected by the Austrian ichthyologist Anton Lamboj in 2009, in a Zootaxa paper (vol. 2173, pp. 41-48) titled 'A new dwarf cichlid genus and species (Teleostei, Cichlidae) from Guinea, West Africa.' Its only species, Enigmatochromis lucanusi, is the type species by original designation and monotypy. The holotype — an adult male of 2 in standard length, catalogued as NMW 95063 at the Naturhistorisches Museum in Vienna — was collected by W. M. Traore in the Foto River near Fria, Guinea, in November 2007; paratype series are held in Vienna (NMW 95064-66), the American Museum of Natural History (AMNH 238830) and the Musée Royal de l'Afrique Centrale in Tervuren (MRAC 2008-015-P). Before its formal description the fish circulated among aquarists and in Lamboj's own 2005 Cichlid News article as 'Pelvicachromis sp. "Blue Fin".' The genus belongs to the chromidotilapiine cichlids, the West and Central African lineage of small, mostly pair-bonding cichlids that also contains Pelvicachromis, Parananochromis, Congochromis, Nanochromis, Benitochromis and Chromidotilapia. Eschmeyer's Catalog of Fishes and FishBase both list Enigmatochromis lucanusi Lamboj, 2009 as the valid name, with no junior synonyms. The name itself records the taxonomic puzzle the fish posed: 'Enigma,' for enigmatic, alludes to its intermediate nature — pigmentation reminiscent of Pelvicachromis but skeletal and anatomical characters closer to Parananochromis — combined with the cichlid suffix '-chromis.' The species epithet honours Oliver Lucanus, the German-born Canadian collector, aquarist and fish importer who helped document the species and its habitat.
Morphology
This is a genuinely small cichlid. FishBase gives a maximum size of about 2 in standard length, and the type series ran from roughly 1–2 in SL, so even large adults are only a few centimetres long. The body is moderately slender, the dorsal head profile smoothly rounded, the snout short, and the caudal fin rounded; the caudal peduncle is short and always deeper than it is long. Lamboj diagnosed the genus chiefly on a combination of skeletal characters: twelve scales around the caudal peduncle (fewer than in Chromidotilapia, Benitochromis, Pelvicachromis or Thysochromis), an infraorbital series consisting of a lachrymal plus three tubular bones with a distinctive gap between the second and third tubular infraorbitals, only four openings of the laterosensory system in the lachrymal, and an upper lateral line clearly separated from the dorsal-fin base. The jaws carry one to three rows of small, regularly set unicuspid teeth, with a few anterior lower-jaw teeth angled backwards; the lower pharyngeal bone is triangular with unicuspid to weakly bicuspid teeth. Sexual dimorphism and dichromatism are well developed. Males run about 10-15% larger than females, with more elongate soft dorsal and anal-fin rays and a longer first pelvic-fin ray whose tip reaches the anal-fin origin. Males are pale brown to greyish with a dark, light-blue-edged spot on the rear of the gill cover, a yellow throat, a pale-yellow dorsal fin with a red margin and thin white submargin, and a caudal fin that is yellow above and reddish below, often peppered with dark dots. Females are the more spectacular sex when in breeding dress: the spiny dorsal becomes iridescent blue with a red margin and a black submargin, the lower gill cover and chest flush blue, and the entire belly and flanks up to about the lateral line glow wine-red. Juveniles of both sexes wear three or four rows of irregular dark spots on a brown ground until, at around 0.5 in, the sex-specific colours emerge.
Habitat
Enigmatochromis lucanusi is, so far, known only from its type locality: the Foto River, a small savannah river in the Konkouré drainage near the bauxite-mining town of Fria, in coastal Guinea north of the capital Conakry, at 10°20.1'N, 13°43.4'W. This places it within the Upper Guinea coastal rivers of far-western Africa, a region of short, forest-fringed streams descending to the Atlantic and noted for high freshwater fish endemism. Field notes supplied by Oliver Lucanus describe a watercourse 10–20 ft wide that shrinks to just 12–35.5 in deep in the dry season, with water clarity of about 4 ft. The river is ringed by dense forest, with frequent fallen trees blocking access to the banks; its margins are heavily overgrown with the aquatic aroid Anubias lanceolata, while exposed boulders and submerged logs carry clusters of the fern Bolbitis heudelotii, and stands of Vallisneria grow wherever sunlight breaks through the canopy. The substrate is fine gravel with scattered larger rocks and boulders. The water is extremely soft and acidic: measurements taken in the dry season of February 2006 returned a general hardness and carbonate hardness of effectively zero, a pH of 5.8, and a temperature of 75 °F. At this site the species lives syntopically with the much larger krib Pelvicachromis humilis, the two sharing the same shaded, boulder-strewn, soft-water habitat.
Feeding
No dedicated wild dietary study has been published for Enigmatochromis lucanusi, but its habits can be read with confidence from its anatomy and from the chromidotilapiine pattern. FishBase places it at a trophic level of about 3.2, consistent with a small benthic micro-predator and omnivore. The jaws, set with several rows of fine unicuspid teeth, and a triangular lower pharyngeal bone bearing modest unicuspid-to-bicuspid teeth are the equipment of a fish that picks small invertebrates and other morsels from the substrate rather than crushing snails or grazing tough algae. In its forest-stream habitat that would mean aquatic insect larvae, micro-crustaceans and other small invertebrates taken from the fine gravel, leaf litter and submerged wood, supplemented by aufwuchs — the film of algae, micro-organisms and detritus coating rocks and roots — and by organic detritus. In aquaria it is reported to take the usual small foods readily: live and frozen brine shrimp, daphnia, cyclops, micro-worms and finely crushed flake, with the small mouth setting a natural upper limit on prey size. It occupies the generalist invertivore-detritivore niche typical of the smaller chromidotilapiines.
Mating
Enigmatochromis lucanusi is a monogamous, pair-bonding cichlid, and the behavioural observations that underpin its description came from eight wild-collected pairs and their captive-bred offspring. Pairs form a bond and defend a shared territory centred on a chosen spawning cave. During courtship, breeding and brood-guarding, fish of both sexes intensify their colours and behave more aggressively than at other times. One behavioural detail proved important enough to feature in the genus diagnosis. In many chromidotilapiine cave breeders — Pelvicachromis, Congochromis and Parananochromis among them — a bold dark longitudinal stripe is the badge of a guarding female during the first weeks of brood care, and is only rarely shown by males. In Enigmatochromis the relationship is reversed: the dark lateral stripe is prominent in breeding and guarding males but only weakly and occasionally visible in females. This sets Enigmatochromis females apart from the females of those related genera and is one of the characters Lamboj used to recognise the new genus. The wine-red flush of a ripe female, by contrast, is a clear courtship and condition signal.
Breeding
In the aquarium Enigmatochromis lucanusi breeds as a biparental cave spawner, the reproductive mode shared across most of its lineage. The female deposits her adhesive eggs inside a cave and both parents guard the clutch, with the female taking the more intensive share of egg care while the male patrols the surrounding territory. The eggs hatch about three days after spawning. The larvae are normally kept on the floor of the original cave — only occasionally moved to a nearby cave — and the young become free-swimming roughly eight to nine days after hatching. Both parents then escort and defend the free-swimming brood for a comparatively long stretch, on the order of five to six weeks, before the fry are independent. Newly free-swimming juveniles are tiny, under 0.5 in total length, and wear the spotted juvenile pattern of three or four rows of dark marks until they begin to colour up. No precise wild fecundity counts have been published; as a small cave spawner the clutch is modest, in keeping with the few-dozen-to-low-hundreds range typical of dwarf chromidotilapiines. The species' very soft, acidic native water (pH around 5.8, hardness near zero) is widely regarded as important for successful reproduction in captivity.
In the aquarium
Enigmatochromis lucanusi is a connoisseur's fish rather than a common import: it surfaces only occasionally in the specialist West African cichlid trade, and its requirements make it a project for an experienced keeper of soft-water dwarfs. Because the fish is small and a single pair holds a modest territory, it does not need a large tank — an aquarium of around 23.5–31.5 in length, well structured, suits a pair — but it does need its water conditions respected. The animals come from blackwater-soft, acidic forest streams, and they are best kept and almost certainly must be bred in very soft, acidic water: a pH on the acidic side (in the region of 5.5-6.5, against a wild reading of 5.8), minimal hardness, and a temperature in the mid-20s °C (the type locality sat at 75 °F). The aquascape should echo the natural biotope — a fine-gravel or sand substrate, plenty of rounded rocks, bogwood and leaf litter, several small caves or cave substitutes such as upturned flowerpots or coconut shells, and subdued lighting. Anubias and Bolbitis, both native to the actual habitat, are fitting and undemanding plants. Tannin-stained 'blackwater' from alder cones or leaf litter helps reproduce the soft, acidic chemistry and shows off the fish's colours. The species is mildly territorial around a spawning site but not a brawler, and it suits a quiet, soft-water community with peaceful upper-water dither fish such as small West African tetras; boisterous or hard-water cichlids are poor company. Provide one cave per pair and a few spares to diffuse aggression, feed varied small live and frozen foods, and keep nitrogenous waste low with regular water changes using suitably soft water. Given those conditions it is a rewarding, jewel-coloured little cichlid; given hard, alkaline tap water it tends to languish and will not breed.
Conservation
Enigmatochromis lucanusi has not been evaluated by the IUCN Red List, and it carries no CITES or CMS listing; FishBase classes it as harmless and of low fishing vulnerability. The conservation concern, such as it is, follows directly from the fact that the species is known from a single small river in coastal Guinea and from nowhere else. A range that narrow makes any fish inherently vulnerable to localised habitat change, and the catchment in question sits beside Fria, a long-established bauxite-mining centre, so siltation, water abstraction and pollution associated with mining and with the clearing of the surrounding gallery forest are plausible pressures on its habitat. None of this has been formally assessed, and the apparent restriction to one locality may partly reflect how little of remote western Guinea has been surveyed for small cichlids rather than a truly pinpoint distribution. Even so, a soft-water forest-stream specialist with no documented second population is exactly the kind of West African dwarf cichlid whose long-term security is tied to the fate of a single, modest watershed.