Cichlid Atlas — the world's cichlid waters, in depth

Taxonomy & naming

Peter Humphry Greenwood described this fish in 1954 as Haplochromis vanderhorsti, from swamp habitat at Katare on the Malagarazi River in what was then Tanganyika Territory (now Tanzania). The holotype, an 111-mm specimen, sits in the Natural History Museum, London (BMNH 1953.11.4.1), with a series of paratypes 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 blends Greek roots: astatos (unstable) and rheos (stream), with chromis, an old name for a perch-like fish — loosely, "the changeable river cichlid," a fitting label for a riverine haplochromine whose jaws are anything but fixed. The species epithet honors the naturalist van der Horst. The fish was later moved out of the catch-all genus Haplochromis and into Astatoreochromis.

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 A. straeleni, even while noting that earlier checklists (van Oijen & Snoeks 1991; Poll & Gosse 1995) had kept it valid. FishBase and the IUCN both now file the fish under A. 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.

Appearance

This is a small-to-medium haplochromine, reaching roughly 5 in (13 cm) standard length; Greenwood's type specimen was about 4.4 in (11 cm). The body is moderately deep and laterally compressed, with a pointed or slightly concave snout. Fin counts run to 16–18 dorsal spines (rarely 19) and, diagnostically, only 3–4 anal spines — usually three — which is one of the features used to separate it from its better-known relative A. alluaudi, which carries more.

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. The 2013 revision noted that live coloration shifts with 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 to reach hobbyists.

Range & 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 A. straeleni circumscription, the range covers the Rusizi, Lukuga and Malagarazi basins plus the Luiche, a small affluent entering the lake just north of the Malagarazi delta. The vanderhorsti-type populations are tied to the Malagarazi system in Tanzania and Burundi. Crucially, the genus splits cleanly by drainage: the Lake Victoria region holds A. 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 — flooded swampy margins, marginal weed beds, and small affluent streams — rather than the main river channel, where collectors have generally failed to find it. It does reach Lake Tanganyika proper, but only marginally: specimens have turned up at river mouths and harbors, including Bujumbura at the lake's north end and Ujiji near Kigoma. FishBase records a tropical range of about 75–82°F (24–28°C). 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 weedy fringes.

Ecology & diet

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.

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 A. 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.

Behavior & breeding

Like the vast majority of haplochromine cichlids, this 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. The anal-fin egg-spots that males carry are the classic haplochromine spawning cue, drawing the female to snap at them as she collects eggs and ensuring fertilization within the brooding chamber.

Field data on its breeding season are thin but suggestive. The 2013 revision found females with eggs at varied stages of development, with those caught in January nearly ready to spawn (eggs about 1.9–2.6 mm across), and inferred that spawning most likely peaks at the start of the short dry season, roughly December to January; whether it breeds at other times remains unknown. Detailed accounts of its social structure and territoriality in the wild are essentially absent from the literature, so claims about aggression or pair behavior should be treated cautiously and by analogy with better-studied relatives rather than as established fact for this fish.

In the aquarium

Be honest up front: this fish is, for practical purposes, not in the hobby. Astatoreochromis vanderhorsti was imported only rarely, decades ago, and Paul Loiselle listed it among the colorful riverine haplochromines that have effectively vanished from cichlid tanks and deserve re-introduction. You will not find it for sale in any normal channel, and the bulk of "care" advice circulating for the name is really generalized to the genus.

What can be said comes from its biology and its hardy relatives. As a snail-eating swamp fish from warm (about 75–82°F / 24–28°C), hard, often alkaline water, it would suit conditions similar to those used for other rift haplochromines, and the genus is reputed to be robust and undemanding — A. alluaudi is even deployed as a biological snail-control agent. A realistic setup would be a roomy tank with open swimming space, some structure, and tankmates chosen for a moderately boisterous mouthbrooder rather than delicate community fish; given the egg-spot, mouthbrooding biology, expect male display and intolerance of rivals at spawning. The honest bottom line, though, is that anyone claiming hands-on experience with vanderhorsti specifically is almost certainly describing a different Astatoreochromis — and that the species' real significance is scientific, not aquarial.

Conservation

Under its current accepted name, A. straeleni, this fish is assessed by the IUCN Red List as Least Concern, most recently reassessed on 11 March 2025 (an earlier assessment dates to 2006). It is widespread across several river basins, of no commercial fishery interest, and not in meaningful aquarium trade, so there is no species-specific collection pressure on it. 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. Sedimentation and nutrient loading from deforested catchments further degrade the lake's nearshore and littoral zones. For a fish that lives in clear, vegetated river margins and the shallow, weedy fringes where rivers meet the lake, the most relevant of these pressures are catchment-scale: shoreline development, swamp drainage, and the sediment and turbidity that smother the clear vegetated water it favors. The lake's pelagic clupeid-and-Lates 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.

Astatoreochromis vanderhorsti

About this species