Taxonomy & naming
Peter Humphry Greenwood described this fish in 1954 as Haplochromis vanderhorsti, in the Annals and Magazine of Natural History, from swamp habitat at Katare on the Malagarasi River in what was then Tanganyika Territory (now Tanzania) — squarely within the Lake Tanganyika basin. The holotype, an 111-mm specimen, sits in the Natural History Museum, London (BMNH 1953.11.4.1), backed by a series of 48 paratypes (44 in London, four at the former E.A.F.R.Oreochromis laboratory) collected the same day. Greenwood paired the description with notes on the pharyngeal apophysis of haplochromine cichlids — a structural detail at the base of the skull that would later become central to classifying this group.
The genus name Astatoreochromis (Pellegrin, 1904) is a portmanteau that fixes the fish's place in the family tree: it blends astatos (Greek for 'unstable, variable,' the same root that names Astatotilapia) with the genus Oreochromis and the old fish-name chromis, marking a haplochromine thought to sit intermediate between those lineages. The species epithet honors the naturalist van der Horst. Greenwood's fish was later lifted out of the catch-all genus Haplochromis and into Astatoreochromis, where it joined the better-known Astatoreochromis alluaudi (of the Lake Victoria region) and Astatoreochromis straeleni.
The larger taxonomic story is unsettled in a way worth stating plainly. A 2013 revision of the genus by Banyankimbona, Vreven and Snoeks (European Journal of Taxonomy 39) concluded that vanderhorsti could not be separated from Astatoreochromis straeleni (Poll, 1944) and treated it as a junior synonym. Eschmeyer's Catalog of Fishes follows that judgment, listing the current status of vanderhorsti as a synonym of Astatoreochromis straeleni, even while recording that earlier checklists (van Oijen & Snoeks 1991; Poll & Gosse 1995) had kept it valid. FishBase and the IUCN both now file the fish under Astatoreochromis straeleni, whose trade name is the 'bluelip haplo.' In short: if you are looking for vanderhorsti today, most current databases will point you to straeleni instead.
Morphology
This is a small-to-medium haplochromine. Under the Astatoreochromis straeleni circumscription FishBase carries a maximum of about 5 in (5 in) standard length; Greenwood's type specimen was about 4.4 in (4.5 in). The body is moderately deep, fusiform and laterally compressed, with a pointed or slightly concave snout. Fin counts run to 16–18 dorsal spines (exceptionally 19) and 8–10 soft rays, with 8–10 anal soft rays and, diagnostically, only 3–4 anal spines — usually three — which is one of the features the 2013 revision used to separate it from Astatoreochromis alluaudi, which carries 4–7 anal spines and 17–19 dorsal spines.
In life the fish is handsome rather than gaudy: grey-yellow over the back, warming to orange-yellow on the gill cover, upper cheek, chest and belly, with the lips and lower cheek washed in iridescent blue — the source of the 'bluelip' name. The anal fin carries several horizontal rows of bright orange-yellow egg-spot ocelli, and the rounded tail is stippled with black dots arranged in regular vertical rows. Females wear the same pattern in muted form, so external sexual dimorphism is slight — the surest sex difference is the female's mouthbrooding role rather than any bold colour or finnage distinction. The 2013 revision noted that live coloration tracks the water itself: fish from turbid, high-conductivity swamps near Lake Tanganyika are markedly darker than those from clearer, more vegetated river reaches. Paul Loiselle, writing in Cichlid News, called the rarely-imported vanderhorsti one of the most colorful riverine haplochromines ever to reach hobbyists.
Habitat
This fish is a creature of the rivers and swamps feeding Lake Tanganyika, not of the lake's famous rocky reefs. Under the broader Astatoreochromis straeleni circumscription, the range covers the Rusizi (on the DR Congo–Burundi border), Lukuga (the lake's outlet, in DR Congo) and Malagarazi (Tanzania) basins, plus the Luiche, a small affluent entering the lake near the Malagarazi delta, and the Lufubu in Zambia. The vanderhorsti-type populations are tied specifically to the Malagarazi system of Tanzania and Burundi. The genus splits cleanly by drainage: the Lake Victoria region holds Astatoreochromis alluaudi, while the Rusizi and Malagarazi populations of the Tanganyika basin are the ones at issue here.
Its preferred haunts are clear, well-vegetated water with high transparency — flooded swampy margins, marginal weed beds, and small affluent streams — rather than the main river channel, where collectors have generally failed to find it; the IUCN assessors add that it favours muddy and sandy bottoms. It does reach Lake Tanganyika proper, but only marginally: specimens turn up at river mouths and harbours, including Bujumbura at the lake's north end and Ujiji near Kigoma. FishBase records a tropical range of about 75–82 °F (75–82 °F), and the IUCN gives a shallow depth band of roughly 0–7 ft, consistent with a fish of weedy fringes and river-mouth shallows. So while this is a 'Lake Tanganyika' cichlid in the catalog sense, it is really a swamp-and-river fish of the lake's catchment, brushing the open lake only at its edges.
Feeding
Astatoreochromis is the East African rift's textbook example of a snail-crusher with a flexible mouth. Greenwood reported that the Malagarazi fish fed mainly on snails, ostracods and insects, and stomach examinations in the 2013 revision corroborated a diet of mollusks (whole and fragmented shells) mixed with adult insect fragments and other invertebrate remains; some guts held plant debris and sand instead. FishBase places it as an omnivore at a trophic level of roughly 3.4, and the IUCN describes it as omnivorous but mainly carnivorous, feeding on insects and gastropods.
The genus's claim to fame is its lower pharyngeal jaw — a second set of crushing teeth in the throat. In Astatoreochromis these teeth are developmentally plastic: studies of the close relative Astatoreochromis alluaudi showed that a sustained hard diet of snails induces robust, molar-like (molariform) teeth on a heavy jaw bone capable of cracking shells, while soft food produces slender, pointed teeth on a lighter bone. It is one of the cleanest cases of diet-induced phenotypic plasticity known in fishes, and it has become a model for how a single genotype can build different feeding machines. The same molariform-to-slender gradient appears in the Tanganyika-basin fish, whose triangular pharyngeal bone mixes flat crushing teeth in front with more cuspidate teeth behind — the toolkit of an opportunist that can mill open a snail when shells are on the menu and switch to softer fare when they are not. That dietary flexibility makes the fish a useful mollusc predator, and Astatoreochromis alluaudi has even been deployed as a biological control agent against the snails that carry bilharzia.
Mating
Like the vast majority of haplochromine cichlids, this is a maternal mouthbrooder, and its courtship runs on the standard haplochromine machinery. The anal-fin egg-spots that the fish carries are the classic spawning cue: a male spreads his anal fin to display the orange ocelli, and the female — having just laid and picked up her eggs — snaps at the spots in an attempt to gather what look like more eggs, drawing milt into her mouth and so fertilizing the clutch she is already brooding.
Detailed accounts of its social structure, pairing and territoriality in the wild are essentially absent from the literature; even the IUCN's field observation amounts to noting that the fish 'usually occurs just as pairs.' Because the species is so rarely studied alive, claims about aggression, harem structure or lek behaviour should be treated cautiously and drawn by analogy with better-known relatives rather than presented as established fact for this fish. What can be said firmly is the reproductive mode and the egg-spot mechanism — both well documented for the genus — and that, as in other riverine haplochromines, spawning is tied to season rather than spread evenly through the year.
Breeding
Astatoreochromis vanderhorsti is a maternal mouthbrooder: the female takes the fertilized eggs into her mouth and incubates the clutch there, releasing free-swimming fry only after they have absorbed the yolk and can fend for themselves — the female alone provides this care, with no documented paternal role. The eggs are large and few, as is typical of mouthbrooders that trade fecundity for protection; the 2013 revision measured ripe eggs at roughly 0.5 in across.
Field data on the breeding season are thin but suggestive. The revision found females carrying eggs at varied stages of development, with those caught in January nearly ready to spawn, and inferred that spawning most likely peaks at the start of the short dry season, roughly December to January; whether the fish also breeds at other times remains unknown. Nothing is published on incubation length, brood size at release, or fry growth for this species specifically — gaps that follow directly from how seldom it has been collected or kept. As a swamp-and-river fish of warm, often hard, near-neutral-to-alkaline water, it would in captivity be expected to brood much as its hardy congeners do, but the honest position is that its breeding biology beyond mode, egg size and rough season is undescribed.
In the aquarium
Astatoreochromis vanderhorsti — or the fish now catalogued under the name Astatoreochromis straeleni — is genuinely rare in the hobby. Paul Loiselle wrote in Cichlid News (July 2014) that it was among the most colorful riverine haplochromines ever to reach hobbyists, but it reached very few: the species is essentially absent from current trade lists, and anyone keeping it today likely obtained specimens through specialist networks or directly from field collections. That rarity means most husbandry guidance must be extrapolated from close haplochromine relatives while being honest about that extrapolation.
The tank should be large enough to absorb the mild but persistent aggression typical of riverine haplochromines. A single pair or a colony of one male with two or three females could be housed in a 90–125-litre (roughly 24–33 US gallon) aquarium at minimum; 40–55 US gal gives more margin for managing any male aggression and accommodates the fish's active, exploratory behaviour. Unlike the rocky-reef mbuna of Malawi, this is a fish of soft-bottomed swamp margins and weedy river fringes, so a sand or fine-gravel substrate suits it better than a bare or cobble-covered floor. Dense planting along the back and sides — Vallisneria works well in hard alkaline water and requires no special CO₂ dosing — combined with a few smooth stones or driftwood pieces will let subordinate fish break line of sight without making the tank feel like a rocky African biotope that the species never actually inhabits. A good external filter providing a moderate, not turbulent, current is appropriate.
Water chemistry must reflect the hard, alkaline conditions of the Lake Tanganyika catchment. The species' documented range is pH 7.0–8.5 and 75–82 °F (75–82°F); in practice, a keeper should target pH 7.6–8.2, moderate to hard water (GH and KH in the 10–20 dH range), and a temperature steady around 77–79 °F. Consistently soft or acidic water — the default in many European and North American homes — is unsuitable and will suppress immune function over time. Regular partial water changes are more effective than chemical buffering for maintaining stable alkalinity.
In terms of tankmates, this fish is best kept with other hard-water East African species of comparable size and temperament. Other mid-sized riverine haplochromines, peaceful to moderately assertive Lake Tanganyika shell-dwellers, or robust non-cichlids from the same basin (certain barbs or synodontis catfishes tolerant of alkaline conditions) are workable options. The fish is not a Malawi mbuna and lacks the sustained high aggression of those species, but it is still a cichlid capable of harassing smaller or more timid fish. Keeping it with soft-water tetras, discus, or any species that cannot tolerate high pH would be a mistake.
Breeding in captivity, following standard haplochromine practice, involves the female mouthbrooding the clutch alone. A dedicated breeding setup — a small species tank with the trio or pair isolated — removes the stress of community competition and prevents other fish from harassing a brooding female. Inexperienced keepers sometimes strip the female's mouth prematurely or disturb the brood tank early; patience is important, since the female should be left to carry the fry to full yolk absorption before any intervention. The most common general mistake with hard-water East African haplochromines is simply keeping them too warm or in water that is too soft: both conditions are associated with higher disease susceptibility, suppressed breeding, and shortened lifespan. With correct chemistry and a varied diet that includes hard-shelled invertebrates — snails, pond snails taken live, or crustacean-based frozen foods — this molluscivore should prove hardy and long-lived by haplochromine standards.
Conservation
Under its current accepted name, Astatoreochromis straeleni, this fish is assessed by the IUCN Red List as Least Concern (Sibomana, assessed 11 March 2025; an earlier assessment dates to 2006). It is an endemic of the Lake Tanganyika basin, widespread across several river systems in Burundi, the Democratic Republic of Congo, Tanzania and Zambia, and — though rarely encountered in catches — common enough across frequently fished waters that no range-wide decline is suspected. It carries no CITES listing. It is eaten locally and may be traded at a small scale, but the IUCN notes it is not in the ornamental trade; its fishing vulnerability is rated low. The one threat the assessors flag is catchment-scale: ongoing habitat degradation from soil erosion and sedimentation as agriculture expands across the watershed. That 'Least Concern' status is a genuine signal and should not be overstated into alarm — this is not a threatened fish.
But the water body it edges into is under real strain, and as a swamp-and-river-mouth species of the Lake Tanganyika catchment it shares in that context. Paleolimnological and isotope work led by O'Reilly and colleagues (Nature, 2003; DOI 10.1038/nature01833) showed that climate warming has increased the lake's thermal stratification and weakened the deep mixing that brings nutrients up, with primary productivity estimated to have fallen by around 20% and fish yields by roughly 30% over the late twentieth century. A later study by Cohen and colleagues (PNAS, 2016; DOI 10.1073/pnas.1603237113) tied warming since the 1940s to declines in commercial fishes and endemic mollusks and to a substantial loss of oxygenated bottom habitat. For a fish that lives in clear, vegetated river margins and the shallow, weedy fringes where rivers meet the lake, the most relevant pressures are exactly those near-shore ones: shoreline development, swamp drainage, and the sediment and turbidity that smother the clear vegetated water it favors. The lake's pelagic fishery feeds four countries — Tanzania, the Democratic Republic of Congo, Burundi and Zambia — whose shared stewardship runs through the Lake Tanganyika Authority; the same basin-wide governance that matters for the fishery matters for the marginal habitats this cichlid depends on. The species itself is secure for now; its lake is not unambiguously so.