Taxonomy & naming
The dikume was described by the British ichthyologist Ethelwynn Trewavas in 1972, in the monograph 'Ecological studies on crater lakes in West Cameroon: fishes of Barombi Mbo' that she published with the limnologists John Green and Sarah A. Corbet in the Journal of Zoology (London) volume 167. The holotype (BMNH 1971.10.20.50) and a series of paratypes are held at the Natural History Museum in London, and the type locality is simply Lake Barombi Mbo, the crater lake to which the species is wholly endemic. Trewavas placed it in a new genus, Konia, which she erected to hold this fish alongside Konia eisentrauti, a species she had named a decade earlier (1962); the two are the only members of the genus, and both occur nowhere on Earth but Barombi Mbo. Konia belongs to the subfamily Pseudocrenilabrinae and, more particularly, to the oreochromine (tilapiine) lineage: molecular work by Schliewen and colleagues has shown that all eleven Barombi Mbo cichlids form a single monophyletic radiation derived from a riverine ancestor close to Sarotherodon galilaeus, which colonised the young crater roughly a million years ago and diversified in place. The flock spans five genera, four of them — Konia, Myaka, Pungu and Stomatepia — found only in this lake. Barombi Mbo is the textbook case for sympatric speciation in a crater lake, and within it the dikume represents the radiation's single excursion into the deep water.
Morphology
Konia dikume is a small, fairly slender cichlid; the largest measured specimen is about 4.5 in in standard length, and most are smaller. The dorsal fin carries roughly 15-16 spines and 11-12 soft rays, the anal fin three spines and 9-10 soft rays. The snout is pointed and the mouth set at a modest upward angle of about 20-30 degrees from the horizontal — the geometry of a fish that takes prey from the water just ahead and above it. The oral teeth are usually arranged in only two series, and the lower pharyngeal bone is distinctively slender and long-bladed, markedly longer than it is wide, separating it from its stouter-jawed lake-mates. The single most arresting feature, though, is one no preserved specimen shows. A freshly caught dikume is so engorged with blood that the capillaries swell and the blood oozes over the body surface, especially around the bases of the fins, staining the fish's silvery ground colour red — a direct, visible consequence of the extraordinary haemoglobin load described below. Live fish carry no dark markings; it is only in preserved material that two to five faint dark blotches surface between the upper lateral line and the dorsal fin, sometimes with a vague stripe along the flank. Sexual dimorphism is not well documented and is assumed, by analogy with its congener Konia eisentrauti, to be slight, with males growing somewhat larger than females.
Habitat
Lake Barombi Mbo is a small (about 415 hectares) but deep volcanic crater lake near Kumba, at roughly 984 ft elevation in the Cameroon Volcanic Line, reaching a maximum depth of about 361 ft. Its surface water is warm, soft, tannin-stained blackwater: in-situ measurements give temperatures of about 75–82 °F, pH near 7.0, conductivity around 670 µS/cm, and a sand-and-leaf-litter bottom in the shallows. The lake is permanently stratified, and this stratification is the whole story for the dikume. Below about 66 ft there is no detectable dissolved oxygen — the hypolimnion is essentially anoxic — so most of the lake's living space is closed to fish. Nine of the eleven endemic cichlids stay in the oxygenated littoral; only two have colonised the deep, and of those only Konia dikume is an obligate deep-water specialist, centred on the zone around 66 ft at the lower edge of the oxygenated layer and ranging into the dark, oxygen-free water beneath it. The lake also carries the volcanic hazard common to Cameroon's crater lakes: dissolved gases (chiefly CO2) accumulate in the deep water, and disturbances of the water column — gas leaks or seismically driven upwelling of anoxic bottom water — have been observed to kill fish at the surface, with the deepwater dikume among the casualties.
Feeding
The dikume is a specialist predator on the larvae of Chaoborus, the phantom midge, and its entire physiology is built around reaching them. During the day these transparent larvae shelter in the lake's deep water, mostly between 30 and 230 ft — well down in the anoxic zone, beyond the reach of an ordinary fish. At dusk they migrate upward to feed on rotifers near the surface, and at dawn they sink back down. The dikume exploits this vertical commute. Green, Corbet and Betney (1973) found that it carries a mean blood haemoglobin concentration of about 16.55 g per 100 ml, with a correspondingly high red-cell count, whereas the other ten endemic cichlids of the lake range only from 5.55 to 8.70 g per 100 ml — the dikume's oxygen-carrying capacity is roughly double that of any lake-mate. Coupled with a large blood volume, this acts as an onboard oxygen store: the fish can dive down into the deoxygenated hypolimnion and stay there long enough to feed on the ascending and descending larvae at twilight, extending a feeding window that the short tropical dusk would otherwise cut short. The dikume appears to be a visual hunter, which makes that extra few minutes of low-light feeding time genuinely valuable. Its slender, long-bladed pharyngeal jaw fits a diet of soft-bodied insect larvae rather than hard-shelled prey.
Mating
The reproductive behaviour of Konia dikume has not been observed in any detail in the wild — its habit of living deep in a stratified crater lake makes it one of the harder Barombi Mbo cichlids to watch — and most of what can be said is inferred from its close relative Konia eisentrauti and from the broader oreochromine lineage to which the flock belongs. The dikume is understood to be a maternal mouthbrooder of the ovophilic (egg-brooding) type that does not form a lasting pair bond, in contrast to Konia eisentrauti, which is a biparental mouthbrooder. In such a system the male does not pair off; instead a ripe female courts and is fertilised, then takes the eggs into her mouth, and the male's role ends at spawning. How and where courtship is conducted in the deep, dim water of the lake is unknown. The flock as a whole shows weak, incomplete behavioural and colour divergence between species, and hybridisation is easy in captivity when lake-mates are mixed, which hints at courtship signals that are subtle rather than flamboyant.
Breeding
No breeding of Konia dikume has been documented, in the wild or in aquaria — the species has essentially never been kept (see below) — so its reproduction is reconstructed from its congener and is, in FishBase's own words, only 'assumed to be the same as in Konia eisentrauti.' On that basis it is taken to be a mouthbrooder that produces a modest clutch of relatively large eggs, which are incubated orally until the young are free-swimming. In Konia eisentrauti the eggs are large and take roughly 22-26 days to reach the free-swimming stage, with the female generally the more reliable parent; the fry emerge large and developed, able to take crushed flake or newly hatched brine shrimp at once and to grow quickly. The dikume is assumed to follow the same pattern, with the important difference that it appears not to pair-bond, so brood care is presumed to fall to the female alone. Clutch sizes for the dikume itself have not been counted; the genus-typical figure is a small clutch (on the order of a few dozen large eggs) characteristic of mouthbrooders that invest heavily in each offspring. Any spawning triggers, nest sites, or fry-development timings specific to the dikume remain unrecorded.
In the aquarium
Konia dikume is, for practical purposes, not an aquarium fish. It is the one Barombi Mbo endemic that has essentially never made it into the hobby: while most of the lake's cichlids — Konia eisentrauti, the Stomatepia species, Pungu, Sarotherodon, Myaka — have been collected, exported and kept by specialists, the dikume has remained a 'last holdout,' rarely if ever brought into captivity and not, to any reliable report, bred there. The reason is built into its biology. This is a fish adapted to live at the boundary of an anoxic deep layer, hunting in oxygen-free water on a single prey item (Chaoborus larvae) that migrates vertically through a stratified water column; almost none of that can be recreated in a tank, and capturing the fish at all means working the deep water of a remote crater lake. Anyone who did obtain dikume would face a fish of unknown husbandry, presumably requiring warm (about 75–82 °F), soft, near-neutral blackwater matching the lake (pH near 7.0, low-to-moderate hardness), a dimly lit aquarium, and a diet built around small live invertebrates such as midge larvae, daphnia and similar zooplankton taken from the water column. As with its lake-mates it would hybridise readily with congeners, so it could only responsibly be kept as a single species. Realistically, though, the honest statement is that the dikume is a wild specialist with no established place in aquarium keeping, and its conservation value lies in the lake, not the tank.
Conservation
Konia dikume is assessed by the IUCN Red List as Critically Endangered (criteria B1ab(iii)+2ab(iii)), assessed in 2009 by T. Moelants and published in 2010, with the population trend recorded as unknown. The category follows directly from the fish's geography: its entire world range is one small crater lake, so any degradation of Lake Barombi Mbo threatens the species in a single stroke. The lake sits beside the rapidly growing town of Kumba and faces a familiar suite of human pressures — fishing, agriculture and deforestation on the steep crater rim with the erosion that follows, damming of the outflow to stabilise the water level, pesticide runoff from surrounding cocoa cultivation, and the introduction of non-native fishes — all of which act on a water body small and self-contained enough to be acutely vulnerable. Layered on top is a hazard peculiar to Cameroon's crater lakes: the deep water holds dissolved volcanic CO2, and a sudden overturn or gas release of the kind that proved catastrophic at nearby Lakes Nyos and Monoun could deoxygenate the lake and cause mass fish mortality. The dikume is doubly exposed here, because it already lives at the edge of the lethal deep layer; observed disturbances of the water column have brought dead dikume to the surface. As the lake's only obligate deep-water cichlid, with no captive insurance population, it is among the more precarious members of an already wholly Critically Endangered flock.