Taxonomy & naming
The species was described by the Belgian ichthyologist Max Poll in 1944 as Haplochromis straeleni, from material taken in the Lukuga River — Lake Tanganyika's only outlet — near Albertville (now Kalemie) in the Democratic Republic of the Congo, which stands as its type locality. The epithet honours Victor van Straelen (1889-1964), the Belgian palaeontologist and carcinologist who directed the Royal Belgian Institute of Natural Sciences and chaired the institute overseeing the Belgian Congo's national parks. The species was later moved to the genus Astatoreochromis Pellegrin, 1904 — a name coined for fishes thought intermediate between Astatotilapia and Oreochromis, a fitting label for a riverine haplochromine that wanders the margins of a lake.
For decades a second nominal species, Astatoreochromis vanderhorsti (Greenwood, 1954) from the Malagarazi, was recognised alongside it. The most thorough modern treatment — Banyankimbona, Vreven & Snoeks's 2013 revision of the genus in the European Journal of Taxonomy — examined 185 specimens and synonymised vanderhorsti with straeleni, concluding the Malagarazi fish were simply Astatoreochromis straeleni; the IUCN, FishBase and the Catalog of Fishes all carry vanderhorsti as a junior synonym. That revision is the backbone of the taxonomy used here, and it leaves the genus with just two valid species: the widespread, lake-flock Astatoreochromis alluaudi of the Victoria–Edward–Kyoga region, and this Tanganyika-basin endemic. Trade and field guides call it the "bluelip haplo"; local fishers fold it into generic Bantu names for haplochromines (recorded as "Ndomo," and elsewhere "Ifuro," "Ikijori," "Inunge").
Morphology
This is a small-to-medium cichlid with a moderately deep, slightly compressed body and a pointed snout. FishBase lists a maximum of 5 in standard length, while the 2013 revision records the largest examined specimen at 4.5 in SL — the holotype of the old "vanderhorsti" — and biotope sources quote roughly 4.5 in total length. In short, expect an adult of four to five inches, with most museum material smaller.
Live fish are dark grey-yellow above, shading to orange-yellow on the gill cover, cheek, chest and belly. The diagnostic touch is the iridescent blue wash on the lips and lower cheek that gives the bluelip its name. Fins are orange-yellow, the dorsal edged in red toward the rear, and the anal fin carries three to five horizontal rows of bright orange-yellow egg-spots (ocelli) — many more, and in more rows, than a typical riverine 'Haplochromis'. Coloration also tracks the water: fish from high-conductivity, muddy swamp water near the lake run darker than those from clearer upstream pools. Against its only congener, Astatoreochromis straeleni is told apart by its anal-fin spine count: 3–4 (usually 3) versus 4–7 (usually 5–6) in Astatoreochromis alluaudi, with 16–18 dorsal spines versus 17–19.
Sexual dimorphism is weak by cichlid standards. Females show the same anal ocelli, only smaller, and the sexes differ little in colour or finnage — which makes sexing resting fish by eye genuinely difficult, with reliable separation usually coming only when females are gravid or holding.
Habitat
Astatoreochromis straeleni is endemic to the Lake Tanganyika basin, but it is fundamentally a river-and-swamp fish rather than a lake fish. Confirmed records come from the Rusizi (the inflow on the Burundi–DR Congo border), the Lukuga (the lake's outlet to the Congo), the Malagarazi and its affluents, the small Luiche River near the Malagarazi delta, and the Lufubu in Zambia — spanning Burundi, the Democratic Republic of the Congo, Tanzania and Zambia. It does enter Lake Tanganyika proper, but mostly at the edges: specimens have been taken in the harbours of Bujumbura and Ujiji (near Kigoma), essentially at river mouths.
In the field it favours clear, slow water with submerged and marginal vegetation — the swampy flooded zones of the Gatumba marshes near the Rusizi mouth, vegetated stretches of small Malagarazi tributaries, and quiet swamp pools — over muddy and sandy bottoms. It is notably absent from the main channels of the larger rivers and from the open rocky lakeshore that defines the classic Tanganyika cichlid biotope. IUCN classifies its habitat as inland wetlands (rivers, streams and the lake margin) and places it in shallow water, giving an upper depth of 0 ft and a lower limit of just 7 ft — a top-of-the-water-column fish. So while it shares an address with Tropheus and the featherfins, it lives a very different life: a wetland generalist on the basin's soft-bottomed fringe.
This is a hard-alkaline-basin fish of soft-bottomed margins — the wild water is warm (about 75–82 °F) and runs to Tanganyika's alkaline, high-mineral chemistry. No pH has been measured for the species specifically, but the basin frames the envelope: open Lake Tanganyika is strongly alkaline (pH roughly 8.5–9.2), while the rivers, swamps and tributary mouths this fish actually favours trend somewhat lower (around 7.5–8), so a hard, alkaline range of about pH 7.5–9 is the honest expectation. For the rare keeper who sources it, the natural history implies a riverine-swamp aquascape rather than a rock wall: a sand or fine-gravel bottom, generous planting or root and leaf cover, open swimming space, and calm, gently moving water, with a tank on the order of 50 gallons (around 55 US gal) suiting a small group.
Feeding
The genus Astatoreochromis is best known as a mollusc specialist, and Astatoreochromis straeleni carries the equipment for it: a triangular lower pharyngeal jaw whose central tooth rows mix molariform (flattened, crushing) and enlarged cuspidate teeth, with slimmer pointed teeth along the margins — a mill for cracking snail shells. Greenwood reported the Malagarazi fish feeding mainly on snails, ostracods and insects, and gut contents examined in the 2013 revision bore this out: snails (whole and crushed) alongside insect fragments and other invertebrate remains, with some individuals instead packed with debris, sand and plant fragments. IUCN summarises it as omnivorous but mainly carnivorous, feeding on insects and gastropods.
The honest reading is "durophagous omnivore": a fish built to crush hard-shelled prey but flexible enough to take insects, crustaceans and plant matter as conditions dictate. (It is worth flagging a common conflation — the dramatic, diet-induced plasticity of the pharyngeal mill documented in laboratory work belongs to its congener Astatoreochromis alluaudi; that specific experimental story should not be transferred wholesale to straeleni.) FishBase places it around trophic level 3.4. In the basin's wetlands it functions as a mid-level invertebrate predator, and it is rarely abundant — even where it occurs it tends to turn up in ones and twos rather than schools. As a snail-crusher in captivity it is happiest on snails, frozen and live invertebrates and quality prepared foods.
Mating
Like the rest of its genus, Astatoreochromis straeleni is a maternal mouthbrooder, and its day-to-day social life is built around that strategy rather than fixed, defended territory. It usually occurs as scattered pairs rather than the dense, hyper-territorial aggregations of the rock-dwelling Mbuna template, and biotope keepers describe it as generally peaceful, with territoriality flaring mainly around spawning. The many-rowed anal ocelli on the male play the usual haplochromine role in mouthbrooding courtship, standing in for the eggs as the female turns to mouth them and so prompting the male to release milt near her clutch.
Because sexual dimorphism is muted — females wear the same ocelli, only smaller, and the sexes are close in colour and finnage — there is little of the showy male nuptial display seen in the lake's open-water haplochromines, and pair formation is correspondingly low-key. For aquarists, the practical consequence is that this is not a fish to sex or pair on sight; reliable identification of a ready female usually waits until she is gravid or carrying.
Breeding
Astatoreochromis straeleni is a maternal mouthbrooder: the female takes the fertilised eggs into her mouth and incubates them there, releasing fully formed, free-swimming fry that she guards briefly afterward. The 2013 revision found females with ovarian eggs at varying stages — the most advanced, near-spawning eggs measuring 0.5 in in diameter — and mouthbrooding females with empty guts, since they fast while holding. The pattern of egg development across collecting months suggests spawning concentrated at the start of the short dry season, around December to January, though whether that is the only breeding window is unresolved.
No one has counted a straeleni clutch in the wild, but the numbers are necessarily modest: a mouthbrooding female's buccal capacity is limited, and the eggs are large (the most advanced run 0.5 in), so a small clutch on the order of a few tens of eggs is the genus-typical expectation — FishBase's own resilience model assumes a fecundity below 1,000. There is no paternal care: the male's contribution ends at fertilisation, after which the female alone broods and shelters the young. Detailed fry-development and brood-size data specific to straeleni in the wild remain thin, and much of what is inferred about its reproduction comes from the better-studied congener Astatoreochromis alluaudi and from the genus's general biology rather than from dedicated field study of this species.
In the aquarium
Astatoreochromis straeleni is, to be direct about it, a fish you are unlikely to find for sale. It has no established presence in the ornamental trade and almost none in hobbyist literature; when it has appeared in tanks it has been via specialist collectors or cichlid-society fish-room swaps rather than any pet-trade supply chain. That rarity is worth stating plainly before anything else, because the keeper who does obtain it deserves an honest picture of what they are working with rather than the usual optimistic prose.
Tank size and water chemistry follow directly from the species' biology. As a fish reaching 4.5–5 in total length that can be territorial around spawning, a minimum of 50–55 US gal is appropriate for a pair, and more space is better if you intend to keep a small group or add other species. Water chemistry must be hard and alkaline throughout: target pH 7.8–9.0, high hardness (GH 15° dH and above is appropriate), and temperature 75–82 °F, matching the Lake Tanganyika-basin envelope. Soft or acidic water — the default tap water in many parts of Europe and North America — is not suitable and should be hardened with appropriate salts before introducing fish. Filtration should be efficient but the current gentle; this is a wetland and river-mouth fish, not a fast-riffle species.
Decor should reflect the actual biotope rather than the classic Tanganyika rock wall. A fine sand or small-gravel substrate suits its habit of sifting and overturning the bottom in search of snails and invertebrates. Planting is appropriate and welcome — the species occupies vegetated swamp margins in the wild — though the substrate-rooting of plants should be anchored with rocks given its tendency to disturb the bottom. Driftwood, root tangles, or leaf cover further recreate the marginal-wetland character of its natural range. Open swimming space should also be provided, since it is not exclusively a hide-and-ambush fish.
Diet is straightforward: feed snails whenever practicable (the fish is built to crush them and thrives on them), supplemented by frozen and live invertebrates — bloodworm, brine shrimp, Daphnia — and quality prepared cichlid pellets or wafers. Dry flake-only diets do not reflect its durophagous, carnivore-biased nature and should be a minor component at most. The important caution — generalising from the congener Astatoreochromis alluaudi, which is the cichlid used in laboratory studies of pharyngeal-jaw plasticity — is that this species' snail-crushing apparatus is most effectively maintained when hard-shelled prey form a real part of the diet rather than a curiosity.
Tankmate selection requires care. As a territorial haplochromine that is capable of real aggression around spawning, it should not be kept with significantly smaller or more timid species that cannot hold their ground. Other Tanganyika-basin species of similar size and temperament — robust riverine or bay-shore cichlids, or medium-sized Julidochromis if the aquascape suits both — can coexist if space is adequate, but the keeper should monitor closely. Within the species, a single pair or a male with two or more females reduces male-on-male aggression; a lone male with a single female risks the female being harassed in a confined space. Breeding is straightforward in principle: it is a maternal mouthbrooder, the female holds the fertilised eggs in her buccal cavity and later guards free-swimming fry, and no paternal care is offered. Broods are small (consistent with the large, 0.5 in eggs); separating a holding female into a smaller tank avoids disruption and fry predation. The main keeper mistake — beyond failing to provide hard alkaline water from the outset — is assuming this fish shares the rock-and-cave template of the lake's better-known cichlids; it does not, and an all-rock tank with no soft substrate or plant cover is a poor environment for it.
Conservation
Astatoreochromis straeleni was reassessed for the IUCN Red List on 11 March 2025 (assessor C. Sibomana; reviewer N. Muderhwa) and listed as Least Concern, carrying forward the same category it held in 2006. The rationale: it is a basin endemic of streams, swamps and river mouths, and while real threats exist, there is no evidence of declines steep enough to warrant a threatened listing. Its population size and trend are simply unknown — it is rarely taken even in frequently fished waters, and tends to occur as scattered pairs. The threat IUCN flags is continuing habitat degradation from watershed erosion and sedimentation driven by expanding agriculture; collection pressure is essentially nil, since the fish is eaten only locally and is not in the ornamental trade.
That species-level calm sits inside a basin under genuine strain. Lake Tanganyika has warmed measurably, and stronger, more persistent stratification has reduced deep mixing and the nutrient upwelling that fuels the food web: O'Reilly and colleagues (2003, Nature, doi:10.1038/nature01833) linked this warming to roughly a 20% drop in primary productivity and an estimated decline of around 30% in fish yields. Paleoecological work by Cohen and colleagues (2016, PNAS, doi:10.1073/pnas.1603237113) documented warming-driven losses of oxygenated benthic habitat and declines in commercial fishes and endemic molluscs. Those pressures bear most directly on the lake's pelagic clupeid (Stolothrissa, Limnothrissa) and Lates fishery that feeds four nations, and on deep- and rock-dwelling endemics — and the basin's shoreline and wetlands face added sedimentation as catchments are cleared. Astatoreochromis straeleni's exposure runs through that last channel: as a soft-bottomed wetland and river-mouth fish, it is most vulnerable to siltation and the degradation of marginal swamp habitat, exactly the threat IUCN names, rather than to the open-water productivity collapse. Management of the lake is shared across Burundi, the DRC, Tanzania and Zambia under the Lake Tanganyika Authority. The accurate summary is the careful one: the species itself is Least Concern, but the lake it belongs to is not without trouble, and the wetlands this particular fish depends on are the part of the basin most easily lost to erosion.