Taxonomy & naming
Aulonocara guentheri was described by the British-South African ichthyologist David H. Eccles in 1989, in the monograph Malawian Cichlid Fishes: The Classification of Some Haplochromine Genera that he co-authored with Ethelwynn Trewavas. The species had spent the previous seven decades hidden inside another name. When Regan diagnosed Aulonocara nyassae in 1922 he based it on three syntypes that, as Eccles later recognised, in fact belonged to two different species; choosing the specimen matching Regan's figure as the holotype of Aulonocara nyassae left the remaining material to be described as a distinct fish, Aulonocara guentheri. As a result the two species literally share type specimens — the holotype of Aulonocara guentheri (BMNH 1921.9.6.221, with one paratype BMNH 1921.9.6.222 in the Natural History Museum, London) is also part of the original type series of Aulonocara nyassae. The name had accordingly been applied as 'Aulonocara nyassae (part)' by Regan (1922), Trewavas (1935), Jackson (1961) and others before Eccles untangled it. The genus Aulonocara belongs to the haplochromine cichlids (Cichlidae: Pseudocrenilabrinae) and is divided into rock-dwelling and sand-dwelling groups; Aulonocara guentheri sits firmly among the sand-dwellers reviewed by Ad Konings (1995), the foremost authority on the genus. Konings diagnoses it as a small-to-medium sand-dweller separable from its close relatives by a suite of head proportions — it differs from Aulonocara nyassae in its smaller eye, longer snout and deeper preorbital; from Aulonocara rostratum in its larger eye and longer lower jaw; from Aulonocara gertrudae in its longer snout and smaller eye; and from Aulonocara brevinidus in its smaller eye, longer lower jaw and deeper preorbital.
Morphology
This is a small-to-medium Aulonocara that attains roughly 4.5 in (about 4.5 in) standard length, the figure given by Konings (1995); FishBase lists a maximum of about 6 in total length for males and 5.5 in for females, which is consistent once the tail is included. The body is the moderately elongate, laterally compressed shape typical of the sand-dwelling peacocks. The defining features of Aulonocara are not colours but bones: the sensory canal system of the skull is greatly expanded, with the pores of the preorbital (lachrymal), the preoperculum and the lower jaw so enlarged that they almost entirely occupy those bones, and the infraorbital bones in particular are swollen to house the sensory apparatus. Eccles further characterised the genus by infraorbitals so expanded that they exclude scales from most or all of the cheek. In life the pigmentation runs to vertical bars rather than horizontal stripes. The single most useful field mark in Aulonocara guentheri is shared by both sexes: a distinct yellow colour over the lower half of the head. Sexual dimorphism follows the usual peacock pattern — males in breeding (nuptial) dress are more strongly and brightly coloured, with the blue iridescence characteristic of courting Aulonocara males, while females and non-territorial males are a much plainer light sandy-yellow to silvery, a cryptic livery suited to life over pale sand.
Habitat
Aulonocara guentheri is endemic to Lake Malawi and the adjoining Lake Malombe, restricted to the southeastern arm of the lake. Konings (1995) reports it as common in the southeastern arm, occasionally taken in beach seines at Senga Bay, and records his own observations at Monkey Bay, near Kadango, near Makanjila Point, and at Thumbi East Island (the type material was collected at Thumbi East Island in December 1989). The IUCN range description adds Domira Bay and Nkhotakota to the historic distribution. It is a fish of shallow, open sandy habitats; Konings describes it as a common cichlid of shallow sand where it forages in the open, and individuals have also been seen over bare sand at depths of about 49–66 ft near Thumbi East Island. Like the other sand-dwelling Aulonocara it keeps to depths shallower than about 164 ft and does not appear to be tied to any specific stretch of coast, ranging widely over suitable substrate rather than holding to a rocky reef. Lake Malawi itself is warm, clear and strongly alkaline soda water, typically around 75–82 °F in the surface layers with a pH near 7.7–8.6 — the broad chemical envelope shared by the lake's haplochromine community.
Feeding
Aulonocara guentheri is a sand-sifting invertivore that hunts by the genus's signature 'sonar-feeding' technique. The fish hovers almost motionless 0.5 in above the sandy bottom while its enormously enlarged cephalic sensory canals register the slightest movement of prey hidden in the substrate; once a buried invertebrate is located, the cichlid makes a sudden downward dive, plunging its snout into the sand to seize it. Konings notes that this behaviour is so diagnostic that an unknown fish can be assigned to Aulonocara on feeding technique alone. The diet is the small invertebrate fauna of the sand — insect larvae and crustaceans that the IUCN assessment lists explicitly. In the community Aulonocara guentheri is one of several sand-dwelling cichlids working the same open-bottom larder; it forages in small groups of roughly ten and these parties frequently mingle with other sand-dwelling species, a mixed-shoal foraging habit common on Malawi's sand flats.
Mating
Outside of breeding, Aulonocara guentheri is a loosely social fish: males and females (the latter recognisable by the yellow on the lower head) move together in small foraging groups of about ten and mix freely with other sand-dwellers. Reproductive behaviour has not been directly observed underwater, but its outline can be reconstructed from the catch record. Konings notes that males with full territorial (breeding) coloration were never seen in the wild, yet such nuptial-dress males were rather commonly taken in the beach seines of local fishermen in November and December in the early 1990s. The inference, drawn by both Konings and the IUCN assessment, is that males establish temporary spawning territories — defended only briefly rather than held as permanent rocky stations — and that spawning may be concentrated in a restricted season around November–December. Because mouthbrooding females were never observed in the act, it remains unclear exactly how and where courtship and pairing play out; more field observation is needed before the breeding season can be confirmed.
Breeding
As a haplochromine peacock cichlid, Aulonocara guentheri is a maternal mouthbrooder: after spawning the female takes the fertilised eggs into her mouth and incubates the developing young there, providing all of the parental care while the male contributes only sperm and a transient territory. This is the universal reproductive mode of the Aulonocara and of Lake Malawi's haplochromines generally. The specifics for this species have not been documented in the wild — no brooding females were observed during the field studies, and clutch size, brooding duration and fry development have not been recorded for Aulonocara guentheri itself. What field evidence exists points only to the likely timing and setting: territorial males in nuptial colour appear in the catch in November and December, suggesting a possibly restricted breeding season and spawning at temporarily defended sites on the open sand rather than at a fixed nest. Beyond that, breeding remains essentially undescribed for this particular peacock.
In the aquarium
Aulonocara guentheri is one of the less commonly traded peacocks — the trade is dominated by the showier and more easily bred colour-morphs of Aulonocara nyassae and Aulonocara stuartgranti, and Aulonocara guentheri's Endangered status means wild-caught imports are negligible. That said, captive-bred stock does circulate modestly among specialist Malawi keepers, and for those who can source it the fish is fully manageable as a peacock cichlid of somewhat larger-than-average stature. A tank of 50 US gal (roughly 4 feet / 47 in) is the practical floor; given that males approach 5.5–6 in total length and need swimming room as well as defined territory, a 240-litre or larger aquarium is preferred, especially if other cichlids are to be housed alongside. As with all Lake Malawi sand-dwellers the substrate should be fine, pale sand at least 2 in deep — this fish evolved specifically to plunge its snout into sand to catch prey, and it will do so daily in captivity. Rocks and flat stones arranged into open caves and crevices along the back and sides of the tank give the male a spawning territory and provide retreat space for females and subordinates, while leaving a generous open-sand foraging floor in the middle and front.
Water chemistry should mirror Lake Malawi's: temperature 75–82 °F, pH 7.7–8.6, and moderately hard to hard (GH/KH target roughly 10–20 dH). Many keepers add sodium bicarbonate or a prepared Malawi salt mix to raise and buffer alkalinity, particularly in soft-water regions. Filtration must be efficient — peacocks are heavy eaters and produce substantial waste — but surface agitation should be moderate rather than violent; the fish are not from a turbulent environment. Weekly water changes of 25–30% are advisable to maintain the stable chemistry Lake Malawi cichlids expect.
In terms of tankmates, Aulonocara guentheri mixes best with other peacock cichlids of differing coloration and with the gentler Haplochromis/Aulonocara-group 'haps', provided the tank is large enough to dilute aggression. The critical caution with any Aulonocara is hybridization: a male Aulonocara guentheri will court females of other peacock species and the resulting hybrids cloud the gene pool of captive fish. Keepers serious about the species keep it either as a species group or pair it only with peacocks so visually distinct that mis-spawning is unlikely. Mbuna (rock-dwelling cichlids from the genus Pseudotropheus, Labeotropheus, etc.) are generally poor companions — many are substantially more aggressive than the relatively placid sand-dwelling peacocks and will bully them relentlessly, particularly in smaller tanks.
The recommended social structure is the harem typical of Aulonocara: one male with three or more females. A second male in any tank under about 78.5 in will generally result in one being worked to exhaustion or death. Feeding is straightforward — Aulonocara guentheri accepts quality sinking pellets and granules, frozen or live bloodworm, Daphnia, Mysis shrimp, and similar invertebrate fare; avoid high-protein mammalian meat products (beef heart, etc.) which can cause digestive problems in cichlids evolved on invertebrates. High-carotenoid foods support male colour development.
Breeding in captivity follows the standard peacock template: a courting male will display intensely to a receptive female over the sand, circling and flaring; spawning occurs on the open sand or a flat stone, with the female picking up the eggs and fertilising them by mouthing the male's vent or egg-spots on his anal fin. She then holds the developing fry in her buccal cavity for roughly three to four weeks (genus-typical; not precisely recorded for this species). The female should be left in the main tank or moved to a quiet holding tank rather than stripped prematurely; she will typically release free-swimming fry that are already large enough to take Artemia nauplii and finely crushed pellet immediately. Common keeper mistakes include maintaining too-soft or too-acidic water (which suppresses colour, immune function and breeding), keeping only one female (which leads to a single female being harassed to death), and mixing multiple male peacocks of similar appearance (which invites hybridization and intensified male competition).
Conservation
Aulonocara guentheri is assessed by the IUCN Red List as Endangered (EN, criterion B1ab(v)), assessed on 23 May 2018 and published in the 2019 amended assessment by Ad Konings (reviewed by Kanyerere, Phiri & Snoeks). This is a sharp downgrade from its 2006 Least Concern listing, and the reason is overfishing. The species was a common component of beach-seine catches in the southern lake through the 1980s and early 1990s, but most subpopulations have since been extirpated; it no longer appears in the Senga Bay seine catches where it was once routine, and it has not been seen or reported outside Domira Bay since 2010. It is now considered extant only at Domira Bay — a single location with an extent of occurrence of about 155 mi² — and possibly extinct across the rest of its former range, with the remaining population still declining (a survey comparison indicated roughly a 45% drop over a decade, from about 7.6 kg per haul in 1998–1999 to 1.7 kg in 2016). The driver is intensive beach-seine and gillnet fishing in the shallow sandy habitats this fish depends on; it is taken by subsistence fishermen and is no longer a target of the ornamental trade. It may persist within the Lake Malawi National Park at Thumbi East Island, which offers the species its best prospect of protection.