Taxonomy & naming
The bluegray mbuna was described in 1973 by the British-trained fisheries biologist Digby H. Eccles, working from the Lake Malawi research station, in a short paper in Arnoldia (Rhodesia) that named two new cichlids at once. Eccles placed it in Pseudotropheus as Pseudotropheus johannii, the original combination, with the holotype (USNM 210702, now in the Smithsonian's National Museum of Natural History) and a paratype taken from the rocky shore just south of Cape Ngombo on the lake's eastern side. For most of its life in the hobby and the literature the fish has been called Pseudotropheus johannii — Maréchal adopted that combination in the 1991 CLOFFA checklist, and it became the name on dealer tanks worldwide. The genus has never sat comfortably, however. Melanochromis (Trewavas, 1935) was originally separated from Pseudotropheus on the slim basis of a horizontally striped colour pattern, a character that later work showed to be a poor guide to actual relationships. When Konings and Stauffer revised the johannii group in 2012 they returned the species to Pseudotropheus, and Eschmeyer's Catalog of Fishes, Konings' 2016 atlas, and the current IUCN assessment all now treat Pseudotropheus johannii as the valid name, with Pseudotropheus johannii listed as a synonym. The atlas retains the long-familiar Melanochromis combination as its headline because that is how the fish is overwhelmingly known and traded, but readers should understand the two names refer to the same animal and that the formal taxonomic preference has shifted to Pseudotropheus. The species belongs to a tight cluster of look-alikes — alongside Pseudotropheus interruptus, Pseudotropheus perileucos and, most importantly, Pseudotropheus cyaneorhabdos (the 'maingano') — whose blue-and-black males are very hard to tell apart.
Morphology
This is a small, slender mbuna. FishBase gives a maximum of about 4 in total length; malawi.si reports wild adults reaching roughly 4.5 in in males and 3.5 in in females, with both sexes commonly running a few centimetres larger under aquarium feeding. The body is the typical elongate, cylindrical mbuna form built for working rock surfaces. Its defining feature is colour, and specifically the strongly reversed dichromatism that fools newcomers. Dominant males are dark blue to blue-black overall, crossed by two pale electric-blue horizontal stripes — one running along the upper back at the base of the dorsal fin and one along the mid-flank — with a dark submarginal band and pale margin on the dorsal and several yellow-tinged 'egg-spot' ocelli on the anal fin. Females and immature fish are the opposite: a clean, bright yellow to yellow-orange from nose to tail, with only faint darker striping. Juveniles of both sexes start out in this yellow livery, and males darken as they mature and gain status, so a tank can hold individuals at every stage between marigold and midnight blue. Brooding females may briefly flush with traces of the male pattern. The hardest identification problem is not sexing the fish but separating males from the 'maingano' (Pseudotropheus cyaneorhabdos): the two are, as malawi.si puts it, almost indistinguishable as adult males. Useful tells are that johannii females and juveniles are yellow whereas maingano shows blue-on-black stripes in both sexes at all ages, and that maingano tends to be the more slender, electric-blue-bellied of the two. Northern johannii populations near Chuanga and Metangula can further muddy things, as their males may lack the light-blue stripes altogether.
Habitat
Pseudotropheus johannii is endemic to Lake Malawi and, within it, confined to the south-eastern shore. The documented range runs along the eastern coast from Chuanga in Mozambique north to Cape Ngombo at Makanjila Point in Malawi — a fairly narrow strip rather than a lake-wide distribution. It is a fish of the 'intermediate' habitat, the transition zone where rock gives way to sand, and is found mainly at the rock–sand interface though it also enters purely rocky areas. Recorded depths run from about 10–59 ft, but the great majority of individuals are in shallow water; the IUCN assessment puts the typical haunt at around five metres. The water it lives in is the hard, alkaline, oxygen-rich water characteristic of Lake Malawi's rocky littoral: pH generally between about 7.7 and 8.6, conductivity moderate to high, and surface-layer temperatures roughly 75–82 °F through the year. Within its range the species shows the geographic colour variation typical of mbuna, with named local forms (for example the 'Gome' population), the northern stripe-less variants, and trade names such as 'Narungu' attached to particular reefs.
Feeding
Like most mbuna, the bluegray is a grazer of aufwuchs — the dense felt of filamentous algae, diatoms, and the tiny invertebrates, crustaceans and detritus living within it that coats every sunlit rock surface in the lake. The IUCN account, written by Konings, records it feeding from both rock and sand substrates and on suspended matter in the water column, with the diet dominated by blue-green algae and diatoms. malawi.si describes it as omnivorous, taking algae, zooplankton and small invertebrates, and notes that individuals will also pick plankton out of open water. That flexibility — combing the rock biofilm but also sifting sand and snatching drifting plankton — is broader than the rigid scraping specialism of some mbuna, and FishBase accordingly places it at a low trophic level around 2.0. In aquaria this translates into a fish that does best on a vegetable-based diet (spirulina-rich flake or pellet) with modest animal protein; over-feeding rich, meaty foods to an algae-grazer of this kind invites the digestive disorder hobbyists call 'Malawi bloat'.
Mating
Social life in this species is organised around male colour and dominance rather than fixed real estate. The IUCN assessment makes the interesting observation that males do not hold classic feeding territories but instead chase conspecific males in full breeding colour away from the foraging grounds — the blue-black livery itself is the trigger for aggression. In practice a dominant, fully coloured male courts and spawns with a number of yellow females, the polygynous harem arrangement standard among mbuna. Subordinate males that have not yet darkened can often slip by unmolested because they still wear the female yellow. Aggression within the species is intense, particularly male-to-male: where two coloured males meet, one will usually be hounded relentlessly. This is the behavioural fact that most shapes how the fish must be kept, and it is also why a male suddenly losing colour in a tank is a reliable sign he is being suppressed by a rival.
Breeding
Pseudotropheus johannii is a maternal mouthbrooder, like all of Lake Malawi's mbuna. Spawning takes place among the rocks: a coloured male displays to a ripe female, quivering and fanning his anal fin so that its yellowish egg-spots stand out. The female lays a small clutch on the substrate and immediately takes the eggs into her mouth; as she noses at the male's egg-spots — mistaking them for her own eggs — he releases milt, which she draws in, fertilising the clutch inside her buccal cavity. Reported clutches are small, on the order of 10–30 eggs, consistent with the species' modest size. The female then broods for about twenty days, not feeding during incubation, and releases free-swimming fry that are well developed and able to fend for themselves. Unusually for many mouthbrooders, the released fry are not taken back into the mouth at the first sign of danger; they instead disperse into the rocks and often join loose groups of similarly sized juveniles. In captivity the species breeds readily once a settled male-and-harem group is established, and the small broods are easy to raise on powdered or crushed foods.
In the aquarium
Pseudotropheus johannii has been in the trade since the mid-1970s and remains one of the most commonly available mbuna — a status that cuts both ways. Its availability means good stock is findable, but it also means casual impulse purchases that end in frustration. The minimum sensible tank for a group is generally cited in the hobby at around 40–55 US gal of floor length, ideally 47 in or more. The species is territorial and combative, and in a short or overstocked tank a dominant male will methodically injure or kill everyone else. Taller tanks help less than long ones; the fish need horizontal territory, not depth.
The water has to match the Lake Malawi character documented in the wild: pH 7.7–8.6, hard and alkaline (general hardness 10–20 dH is a workable target), temperature 75–82 °F. Malawi tap water adapted to these parameters, or soft water buffered with a proprietary Malawi salt mix, both work. Efficient mechanical and biological filtration is important because mbuna are messy feeders and Malawi's rock pools are naturally oxygen-rich and dilute in organic waste; letting nitrates climb above about 20 ppm stresses the fish and increases susceptibility to disease. Substrate should be fine sand or light-coloured crushed coral — calcareous gravel helps maintain pH — with an extensive rock stack built to the surface. Pseudotropheus johannii spends its time in the lower and middle water column working rock surfaces; open swimming space matters less than the presence of many cave entries and crevices.
The species is best kept in a harem of one male to three or four females. A second male in the same tank is possible only in a very large, heavily divided aquascape, and even then fights are the rule rather than the exception — the moment a second male fully colours up, aggression between the two becomes relentless. Because females and subdominant males wear identical yellow livery, a surplus of yellow fish acts as a buffer: the dominant male cannot target every individual at once. Community tankmates need to be chosen with the same logic that applies to all mbuna: avoid quiet, slow-moving fish that will be harrassed into the corner, avoid other elongate blue-and-black Melanochromis or Pseudotropheus males that will trigger colour-based aggression, and be especially careful about housing Pseudotropheus johannii with Melanochromis cyaneorhabdos (the maingano) or Melanochromis dialeptos, which are similar enough in male colour that interbreeding in the aquarium is well documented. Mixed-mouth brooder pairs involving these species produce fertile hybrids that then contaminate both lineages — a genuine concern if the keeper ever wants to produce or contribute to pure stock.
Diet is where hobbyist mistakes concentrate. This is an aufwuchs grazer — algae, diatoms, and the small invertebrates that live in the biofilm, not chunks of meat. A diet built around high-quality spirulina-enriched flakes or pellets (with spirulina listed near the top of the ingredient list), supplemented with blanched vegetables, is correct. Rich, protein-dense foods — beef heart, tubifex, bloodworm as a staple — push the fat load on a digestive system adapted to low-calorie plant material and are the primary dietary driver of Malawi bloat, the swelling and internal infection syndrome that kills mbuna quickly and resists treatment once established. The occasional small live or frozen invertebrate treat is fine; a protein-heavy daily diet is not. Feed in small amounts two or three times a day rather than one large meal, and do not feed more than the fish consume in two to three minutes.
Breeding in captivity is straightforward once a settled group is in place. A female who has spawned can be left in the main tank in most cases; unless the colony is very aggressive, she will find a sheltered spot to complete her roughly twenty-day hold. Moving her to a separate, well-filtered brooding tank with some rock cover protects the brood from being harassed by tankmates and reduces the likelihood that stress triggers early release. Released fry are small but robust and accept finely crushed spirulina flake from the first day. The main challenge with breeding this species is not getting eggs — it is keeping track of bloodlines if pure stock matters, and preventing cross-spawning with any maingano or dialeptos in the tank. If pure lines are the goal, the simplest solution is a species-only setup: one male of one species, a group of females of the same species, and nothing else that resembles either of them.
Conservation
The IUCN Red List assesses the species (as Pseudotropheus johannii) as Least Concern, in an assessment carried out on 20 June 2018 by Ad Konings and reviewed by Jos Snoeks. The reasoning is straightforward: although endemic to one lake and to one shoreline within it, the fish is widely distributed across many localities along that shore, is common at most of them, and shows a stable population trend. That is an upgrade from earlier assessments — the species was listed as Vulnerable in both 2006 and 2017 — reflecting better knowledge of its true range rather than any recovery. The assessment does flag two specific pressures: collection for the ornamental aquarium trade, where the fish is exported under its scientific name, and sedimentation from soil erosion driven by agriculture and deforestation in the catchment. Neither is judged to threaten the species at the population level today, but both bear directly on a shallow rocky-shore endemic. Lake Malawi as a whole faces mounting strain — shoreline development, nutrient loading and sediment runoff that smother the rock biofilm these grazers depend on, warming that deepens stratification and shrinks the oxygenated layer, and heavy fishing pressure across the basin. For a fish whose entire world is a narrow band of sunlit rock along one coast, the health of that inshore habitat is the variable that matters most, even while its formal status remains reassuringly secure.