Taxonomy & naming
Maylandia glaucos was formally described in 2011 by Patrick J. Ciccotto, Ad Konings and Jay R. Stauffer Jr., in a paper titled 'Descriptions of five new species in the genus Metriaclima (Teleostei: Cichlidae) from Lake Malaŵi, Africa,' published in Zootaxa (volume 2738). The authors placed it in the genus Metriaclima, the name widely used in the aquarium and much of the scientific literature for these moderately slope-faced, bicuspid-toothed mbuna. Eschmeyer's Catalog of Fishes, however, treats Metriaclima Stauffer, Bowers, Kellogg & McKaye, 1997 as a junior synonym of Maylandia Meyer & Foerster, 1984, and accordingly lists the species as valid under Maylandia glaucos — the combination used here. The two names refer to the same fish and the choice between them is a long-running nomenclatural dispute rather than a biological one. Before its description the fish was known to hobbyists and collectors as Metriaclima sp. 'aurora blue,' reflecting its membership in the so-called Aurora group around Maylandia aurora. The holotype (PSU 4487) was collected at Cobwé on the Mozambican coast, and the ZooBank registration for the nomenclatural act confirms its formal availability. The specific epithet glaucos is treated as a noun in apposition.
Morphology
Maylandia glaucos is a small mbuna, reaching about 2.5 in standard length. It has the typical Maylandia body: a moderately deep, laterally compressed shape with a moderately sloped head and bicuspid teeth in the outer row of the jaws — the combination of characters that places it in the genus. Fin counts run to 17–19 dorsal spines with 8–10 soft rays, and 3 anal spines with 7–8 soft rays. The species is most readily recognised by its coloration and a short list of diagnostic features: it lacks the black submarginal band in the dorsal fin seen in many relatives, and combines this with a yellow gular (throat) region and yellow branchiostegal membranes, while females are a light brown with yellow fin margins. This suite distinguishes glaucos from other Maylandia except the closely similar Maylandia chrysomallos and Maylandia benetos; it is separated from those two by tooth counts in the outer row of the lower left jaw (about 14–19, intermediate between the higher count of chrysomallos and the lower count of benetos). Females, by colour alone, are hard to tell from other members of the Aurora group, but differ from Maylandia xanthos in having a shorter lower jaw and from Maylandia aurora in showing 8–11 vertical flank bars rather than six. The living males are the bluish-grey that gives the fish its name.
Habitat
Maylandia glaucos is a Lake Malawi endemic restricted to the Mozambican side of the lake, known only from the rocky coast at Cobwé (the type locality, around 12°08′S 34°45′E). Like all mbuna it is a strict inhabitant of the rocky littoral, living among boulders and broken rock close to shore where encrusting algae grow on the stone. FishBase places it in the warm, benthopelagic zone of the rocky habitat; the lake's general water chemistry applies — hard, mineral-rich, strongly alkaline water with a pH around 8 and surface temperatures in the mid-20s Celsius. The confinement to a few small reefs at and around Cobwé is biologically significant: mbuna are notoriously poor at crossing the stretches of open sand and deep water that separate rocky outcrops, so populations become isolated and ranges stay tiny. This narrow, single-locality distribution is the central fact of the species' natural history and the basis of its conservation interest.
Feeding
Maylandia glaucos is an algae-comber, the classic mbuna feeding mode. Using its bicuspid outer teeth it grazes the layer of filamentous and encrusting algae — the Aufwuchs — that coats the rocks of its habitat, taking with it the small invertebrates, diatoms and detritus bound up in that mat. FishBase estimates a trophic level of about 2.4, consistent with a largely herbivorous, biofilm-grazing diet. The moderately sloped head and jaw geometry of Maylandia are adapted to working the algal carpet at an angle to the rock surface, combing rather than scraping. As with related mbuna, the fish is in practice an opportunistic omnivore that will take planktonic and benthic animal food when available, but the bulk of its natural intake is the rich, productive algal turf of the rocky shore — a food source abundant enough to support the extraordinary density and diversity of mbuna in Lake Malawi.
Mating
Detailed courtship has not been published for Maylandia glaucos, but the species belongs to a group whose breeding behaviour is highly stereotyped and well known. Maylandia are polygynous maternal mouthbrooders with no pair bond. Sexually active males take on their brightest coloration — in this species the blue-grey body — and defend a territory among the rocks, typically centred on a crevice or a cleared patch of rock or sand used as a spawning site. A male courts passing females with lateral displays, quivering and circling, leading a receptive female to the site. Spawning follows the familiar mbuna pattern: the female lays a few eggs and immediately takes them into her mouth, and the male's anal-fin egg-spots are thought to function in the transfer of milt as she does so, ensuring fertilisation inside the buccal cavity. Males play no part in subsequent care and continue courting other females.
Breeding
Maylandia glaucos is a maternal mouthbrooder, as are all members of its genus. The female incubates the fertilised eggs and the developing young in her mouth for roughly three weeks, not feeding meaningfully during this time, until the fry are large enough to be released as free-swimming juveniles; for a short period afterward she may allow them to dart back into her mouth when danger threatens. Clutch sizes in small mbuna of this size are modest, typically on the order of ten to thirty eggs, scaling with the size of the female, though no specific count has been published for glaucos. In aquaria, mbuna of this type breed readily once a dominant male holds a territory and females are in condition, and broods are easy to rear on fine prepared foods and small live or frozen items. The details given here follow the consistent and well-documented reproductive biology of Maylandia and the broader mbuna assemblage rather than a study specific to this species.
In the aquarium
Maylandia glaucos has a real presence in the specialist mbuna hobby, where it circulated as the 'Aurora Blue' from Cobwé before its 2011 description and remains valued for the clean blue-grey of dominant males set against the yellow-trimmed brown of females. It is a tank-bred and collected aquarium fish rather than a fish known only from museum jars, so the husbandry notes below rest partly on genuine keeping experience with the species and its close relatives.
As a small, rock-dwelling mbuna it suits a typical Malawi rock-cichlid setup: a tank of moderate-to-large footprint built up with stacked rock to create caves and territorial boundaries, a sand substrate, and the hard, alkaline water (pH around 8, mid-20s Celsius) these fish require. Strong filtration and good husbandry are important, as mbuna are sensitive to poor water quality and prone to digestive 'bloat' when fed an inappropriate, fat- or protein-heavy diet; a Spirulina- and vegetable-based diet matching their algae-combing biology is best. Like most mbuna, glaucos is territorial and can be aggressive, so it is usually kept in groups with one male to several females, alongside other robust mbuna of similar temperament and with enough rockwork to diffuse aggression. It is a rewarding fish for the Rift-lake enthusiast but, like its relatives, not a candidate for a peaceful mixed community.
Conservation
Maylandia glaucos is assessed on the IUCN Red List as Near Threatened (criterion B1a), in an evaluation dated 22 June 2018. The basis for that listing is precisely its tiny range: the species is known only from a handful of small reefs at Cobwé on the Mozambican coast, and a fish confined to so small an area is inherently vulnerable to any localised disturbance — a single environmental event affecting those reefs could affect the entire population. The describers themselves noted that few fishermen work at Cobwé and that nets cannot easily be drawn over the broken rock, so direct over-fishing did not appear to be an immediate threat at the time of description; the Red List nonetheless flags the species as Near Threatened on range grounds. The wider pressures on Lake Malawi — sedimentation from catchment deforestation, nutrient runoff, intensifying fisheries and climate-driven changes to the lake — bear on all the rock-restricted mbuna, whose narrow, isolated distributions leave them with little resilience. For glaucos the prudent reading is that of a naturally rare, single-locality endemic that warrants continued monitoring.