Taxonomy & naming
Aulonocara gertrudae was described by Ad Konings in 1995, in his review "A review of the sand-dwelling species of the genus Aulonocara, with the description of three new species" (The Cichlids Yearbook, volume 5, pages 26–36, Cichlid Press). Konings has spent decades diving and collecting across Lake Malawi and is, with the Stuart Grant / M. K. Oliver Smithsonian database (malawicichlids.si.edu), the foremost authority on the lake's cichlids. The holotype is a 4.5 in standard-length male collected south of the Nsinje River at Masinje, on the Malawian east coast, on 1 November 1989 by the author, deposited in the Royal Museum for Central Africa at Tervuren as MRAC 94-56-P-45; a series of paratypes (MRAC 94-56-P-46 to -49) was taken at the same locality, with additional material from Cape Manulo, Malawi, and Lupingu, Tanzania.
Before it had a formal name the fish circulated in the hobby and in Konings' own earlier work as Aulonocara sp. "jumbo blue" (Konings, 1990a: 69) and as the "Multispot Aulonocara." Both labels are provisional trade names rather than established common names, and neither is carried here as an alias. Eschmeyer's Catalog of Fishes and FishBase both list Aulonocara gertrudae Konings, 1995 as a valid species, and the IUCN Red List carries an assessment under that name. Konings diagnosed the species against its sand-dwelling congeners on a combination of proportional characters — a shorter caudal peduncle than Aulonocara nyassae and Aulonocara brevinidus, a larger eye and shorter snout than Aulonocara guentheri and Aulonocara rostratum, and a shorter caudal peduncle plus wider interorbital than Aulonocara aquilonium.
Morphology
Aulonocara gertrudae is a small-to-medium sand-dwelling peacock attaining roughly 4.5 in standard length; FishBase gives a maximum of 4.5 in SL and the holotype male measured 4.5 in SL. The body is fusiform and moderately deep (depth 2.4–2.9 times in standard length) with the enlarged cranial sensory pores and weakly developed chin typical of the genus, and the mouth is terminal, with teeth in four to five rows in each jaw and 32–34 scales in a longitudinal series. Fin counts run to a dorsal of XVI–XVIII spines and 9–11 soft rays and an anal of III spines and 8–9 soft rays.
The species is sexually dichromatic, and the difference is marked. Territorial males are deep metallic blue, and the defining mark — the one that gives the fish its "multispot" trade name and lets it be identified in vivo — is a scatter of distinct yellow spots set into the anal fin. Females share a single muted colour pattern across all known populations and are recognised by their yellow ventral (pelvic) fins. Konings noted a modest geographic cline in male colour: males of the northern populations (north of the Ruhuhu River, in Tanzanian waters) carry a bright orange patch on the shoulder that is absent in southern fish. He flagged that the northern populations differ enough in colour and behaviour that they may represent another species, but grouped all populations under Aulonocara gertrudae because the shared diagnostic combination — yellow anal-fin spots in the male and yellow ventral fins in the female — holds throughout the range.
Habitat
Aulonocara gertrudae is endemic to Lake Malawi and is one of the most widely distributed of the sand-dwelling peacocks, occurring along both the western and the eastern shores of the lake. Konings recorded the most northerly population at Ikombe, Tanzania, in the extreme north, and the most southerly at the type locality near Masinje on the Malawian east coast; intervening records include Mdoka, Msuli, Ntekete and Cape Manulo in Malawi, and Nkanda, Makonde, Lupingu and Lundu in the north (Tanzania). On current published localities the species' confirmed range is Malawi and Tanzania within the single Lake Malawi ecoregion; no Mozambican locality has been documented for it, so a Mozambique record should be treated as unconfirmed rather than assumed from the lake's three-country shoreline.
Ecologically it is a fish of sandy bottoms, where it forages in the somewhat muddy sediment that collects near river outlets. Through most of its range it is usually found at depths greater than 49 ft. North of the Ruhuhu River, however, Konings found it exploiting a different, intermediate habitat — at Ikombe, Nkanda, Makonde, Lupingu and Lundu it occurred over a depth band of roughly 10–98 ft. He suggested the outflow of the Ruhuhu River may act as a soft barrier separating the northern and southern populations, and that the different habitat use in the north may be connected to the scarcity of rock-dwelling Aulonocara there. The lake water it lives in is warm, hard and alkaline — broadly 75–82 °F (75–82 °F), pH around 7.7–8.6 and a general hardness on the order of 6–10 dH in the upper water column — the standard chemistry of Malawi's nearshore zone.
Feeding
Like all sand-dwelling Aulonocara, Aulonocara gertrudae is a sand-sifting benthic invertivore that hunts by the genus's distinctive "sonar-feeding" technique, and FishBase places it at a trophic level near 3.6. Konings describes the behaviour in the genus introduction to the same paper: the fish hovers almost motionless a few millimetres above the sandy substrate, its enlarged cranial lateral-line canals and ampullary sensory pores registering the faint movements of prey buried in the sediment, then makes an occasional dive, snout-first, to seize the invertebrate it has located. The feeding method is so characteristic that, in Konings' words, an individual can be assigned to Aulonocara solely by watching how it forages.
Aulonocara gertrudae itself forages mainly in the soft, somewhat muddy sediment that gathers on sandy bottoms near river outlets — a microhabitat rich in the small benthic invertebrates the peacocks specialise on. Its trophic role is that of a benthic micro-predator on infauna rather than an algae-grazer, and the enlarged sensory pores honeycombing its preorbital, preopercular and lower-jaw bones are the anatomical hallmark of that lifestyle. The closely studied Aulonocara stuartgranti has been shown in the laboratory to locate buried invertebrates in total darkness using exactly this lateral-line system, the clearest experimental demonstration of how the whole sand-dwelling group makes its living.
Mating
Aulonocara gertrudae carries the polygynous, lek-like social system shared by the sand-dwelling Aulonocara. Territorial males in nuptial colour gather into breeding colonies, each male digging and defending a spawning crater in the sand. Konings notes that, in the genus generally, these craters are sited roughly two metres apart and — unlike the bowers of many other Lake Malawi haplochromines — lack a raised rim. Females normally forage in separate groups or singly and apparently visit the otherwise all-male breeding colonies only when ready to spawn.
One behavioural wrinkle tracks the geographic cline in coloration: Konings noted that the spawning-site preference of the northern (Tanzanian) males differs from that of southern fish — FishBase records that males there may instead defend a rocky cave or dig a spawning pit against a rock — a difference he suggested may be influenced by the lack of rock-dwelling Aulonocara north of the Ruhuhu River. Courtship and spawning itself had not been directly observed in the wild at the time of description; the account rests on the colony structure and crater-building behaviour seen on the sandflats.
Breeding
Aulonocara gertrudae is a maternal (ovophilous) mouthbrooder, reproducing in the haplochromine pattern. The female lays her eggs in the male's sand crater, takes them into her mouth almost immediately, and broods the developing young in her buccal cavity, foraging little until she releases free-swimming fry; the male contributes no parental care beyond defending the spawning site. Clutches are small, on the order of a few dozen eggs, in keeping with the modest body size and the buccal-brooding strategy — a precise wild count was not published in the original description. Konings recorded that Aulonocara gertrudae, like the other sand-dwellers he reviewed, breeds throughout the year rather than in a tight season.
In the aquarium the species spawns readily under Malawi conditions and is a rewarding colony fish for a keeper who respects its biology: a generous open sand bed to sift, a single male run with several females so his attention is spread, and separation from other Aulonocara, which hybridise freely and would erase the subtle, locality-defined yellow markings within a generation. Because the species carries a real north–south colour cline of its own, keepers who care about provenance should also keep the orange-shouldered northern fish apart from the southern form.
In the aquarium
Aulonocara gertrudae is an intermediate-level Malawi cichlid that suits a keeper who understands the basic framework of a Rift Lake setup but is not demanding about the finer points of the species' natural depth range. A colony of one male and three to five females can be kept comfortably in a 180-litre (about 48 US gallons) tank, though a 240-litre footprint is more forgiving and gives the male room to establish a territory without constantly harrying the females. The species stays small — around 4–4.5 in standard length — but males are territorial enough that cramped quarters encourage chronic fin-nipping and stress-induced colour loss in subdominant fish.
Water chemistry should replicate the hard, alkaline conditions of Lake Malawi's nearshore zone: pH 7.8–8.6, general hardness 8–15 °dH, carbonate hardness 10–18 °KH, and temperature 75–82 °F (75–82 °F). In most areas with moderately hard tap water, regular partial water changes (25–30 % weekly) and a small dose of Rift Lake salt mix are usually sufficient to hold these parameters. The substrate must be sand — a 2–3 in deep bed of fine play-sand or pool sand is ideal, because males excavate spawning craters in it and the species' entire feeding strategy depends on hovering above a soft substrate and snatching up invertebrates it detects through its lateral-line canals. Gravel disrupts both behaviours and should be avoided. Décor consists of stacked flat rocks forming modest overhangs and defined visual barriers between territories; the open-sand foraging zone in the centre of the tank should remain clear of structures.
Tankmate selection is where most keepers go wrong with Aulonocara. The species can coexist with other Lake Malawi sand-dwellers of similar temperament — Copadichromis, non-aggressive Otopharynx, and medium-sized Lethrinops are reasonable choices — and with peaceful utaka-type haplochromines that occupy the open water column rather than competing for the bottom. Hyper-aggressive mbuna (Melanochromis, Pseudotropheus lombardoi, large Labeotropheus) make poor companions: they occupy the same rock-and-sand interface, out-compete the peacock for food, and inflict serious physical damage on a species built for subtle sensory foraging rather than scrapping. Crucially, Aulonocara species hybridise readily, so gertrudae should never be housed with other peacocks; mixing produces fertile but visually degraded hybrids that are difficult to identify and are unwanted by responsible hobbyists. If keeping the orange-shouldered northern colour form, it should also be kept separate from southern fish.
The species is a maternal mouthbrooder and breeds readily once water chemistry and tank structure are right. A female who has taken eggs will typically mouth-brood for 21–28 days before releasing free-swimming fry. She should be left in the main tank if décor provides adequate hiding spots, or moved to a calm, bare-bottomed brooding tank for the last week; stripping early is an option for experienced keepers but risks fry loss if done before day 18. Females can be exhausted and lose condition if a single pushy male is given no respite — the minimum of three females per male is not a suggestion but a practical necessity. Feed the colony a varied diet of frozen or live bloodworm, Daphnia, mysis shrimp, and a quality small-pellet cichlid food; avoid heavily plant- or spirulina-based foods designed for mbuna, and avoid feeder fish that could introduce disease.
Aulonocara gertrudae is not a species seen in every shop; it circulates mainly through specialist Malawi cichlid breeders and the serious hobbyist trade rather than the mass market, and locality-correct fish (particularly the northern orange-shouldered form) are genuinely scarce outside specialist circles. Most fish available are of general 'lake' origin. That scarcity makes finding the species a pleasant small challenge, but also means buyers should ask about provenance before purchasing. As a package — manageable size, vivid blue-and-yellow male, low aggression toward non-peacock tankmates, willing breeder — it is among the more accessible sand-dwelling peacocks once the basic Malawi framework is in place.
Conservation
Aulonocara gertrudae is listed on the IUCN Red List as Least Concern, assessed 22 June 2018 (assessors including Jacqueline Kazembe, P. Makocho and Ad Konings, under the Pan-Africa Freshwater Biodiversity Assessment). The reasoning mirrors that for the other widespread sand-dwelling peacocks: although the species is endemic to a single lake, it is broadly distributed across both the western and eastern shores of Lake Malawi and is recorded over a wide depth range, so no single localised threat is judged likely to put the whole species at risk in the near term. It is collected for the ornamental trade, but its wide range buffers it against the collection pressure that weighs more heavily on narrow-range, single-locality forms. It carries no CITES listing.
Least Concern for the species is not a clean bill of health for its habitat. Lake Malawi as a whole is under mounting strain — over-fishing, heavy sediment and nutrient loading washing off deforested catchments, and measurable warming of the shallow water column that strengthens stratification and trims the upwelling of deep nutrients. For a fish that forages specifically in the soft sediment near river outlets, catchment erosion and the silt it delivers cut both ways: they can smother the fine benthic habitat Aulonocara gertrudae depends on while also burying the invertebrate prey its sonar-feeding is tuned to detect. The species is secure today, but its security rests on the continued health of the lake's nearshore sandflats.