Taxonomy & naming
George Albert Boulenger described the fish in 1898 as Lamprologus compressiceps, working from specimens J. E. S. Moore had collected on his Lake Tanganyika expedition. The syntypes are held at London's Natural History Museum, and the type locality is Kinyamkolo — the old name for Mpulungu, at the lake's southern tip in present-day Zambia. The species name is plainly descriptive, joining the Latin compressus ("compressed") with -ceps ("head") for the narrow, knife-edged head and body.
In 1991 Maréchal and Poll moved the fish, together with the near-identical Altolamprologus calvus, into the new genus Altolamprologus; the prefix alto- ("high" or "tall") flags the deep dorsal profile that offsets the lateral compression. Eschmeyer's Catalog of Fishes lists Altolamprologus compressiceps (Boulenger 1898) as the current valid name, with Lamprologus compressiceps as the original combination. Within the lake's species flock it sits in the tribe Lamprologini, the substrate-brooding lineage that, at roughly a hundred species, is Tanganyika's most diverse. Ad Konings, the foremost authority on the lake's cichlids, recognises only two described species in the genus; a small, shell-associated "dwarf" form sold as Altolamprologus sp. "compressiceps shell" or "Sumbu dwarf" remains undescribed and may be a distinct species. That shell-dwelling dwarf form is itself a specialised predator of other small, shell-dwelling cichlids, and — like the standard form — it operates alone outside the breeding season, pairing up only to spawn (Konings, Enjoying Cichlids).
Morphology
The defining trait is the body itself: extremely flattened side to side, deep from back to belly, and tapering to a small, pointed, almost beak-like head. The eyes sit high and the mouth is protrusible, and the whole animal looks built to be slid edgewise into a gap in the rocks. That compression is not merely cosmetic. It makes the fish thin enough to wedge into cracks broader predators cannot enter, and flexible enough to fold and twist inside them while it probes for hidden prey.
Reported maximum size varies, partly because the two sexes are being measured. FishBase records a maximum of about 5 in total length; Seriously Fish gives males a standard length of roughly 4–5 in against females of 3.5–4 in; and habitat references, including Konings, describe males reaching 4.5–6 in total length with females staying near 3.5 in. Across the sources the takeaway is the same: males are noticeably larger than females — a strong sexual size dimorphism — while colour and finnage barely differ between the sexes, apart from slightly extended fins on mature males.
Colour, by contrast, is highly variable by population. The hobby trade tracks dozens of geographic forms with names like "Kigoma red fin," "gold head," "black," "fire fin," and "anthracite," each tied to a stretch of shoreline. One documented example: a yellow-coloured population occurs around Cape Chaitika, where — per Ad Konings's field notes — it shares its rocky habitat with the White form of the congener Altolamprologus calvus, itself recorded at the same site. The fish it is most often confused with is its congener Altolamprologus calvus; set against Altolamprologus calvus it has a shorter snout, a deeper body, scales that run onto the head, and generally more distinct vertical barring.
Habitat
Altolamprologus compressiceps is endemic to Lake Tanganyika and distributed almost lake-wide, recorded at scores of localities from Burundi in the north down both coasts to the Zambian and Congolese shores in the south. It is a creature of rocky, rubble-strewn shorelines — piled boulders, narrow cracks, and small caves rather than open sand. Tellingly, it is largely absent from isolated rocky outcrops separated by bare substrate, which suggests it does not readily cross open bottom; that habitat-bound life is exactly what fragments it into so many local colour races.
Depth records differ by source and by life stage. Habitat surveys place it most commonly in the upper rocky zone, roughly 3–50 ft (about 3–49 ft), with juveniles drifting into shallower water and adults tending deeper; Seriously Fish notes adults mostly below about 33 ft (33 ft). The undescribed dwarf form turned up in sand near rocks at Cape Mpimbwe at around 80–100 ft (82–98 ft), deeper than the typical rock-dwelling populations. The lake water itself is hard and distinctly alkaline, and in situ the fish lives at a high pH near 8–9; FishBase's listed range of pH 6.5–7.5 sits below the lake's real chemistry and should be read as an outlier rather than a target.
Feeding
This is a trophic specialist on the lake's crustaceans. A stomach-content study of Tanganyika's shrimp-eating cichlids by Yuma and colleagues (1998) found that shrimp dominated its diet, at over 80% of stomach contents, and FishBase places it at a trophic level near 3.6. In the wild it also takes other invertebrates and small fishes, including the fry of other cichlids, hunting by inserting its compressed head and protrusible mouth into rock crevices broader-bodied predators cannot reach, then suction-feeding prey from inside the gap.
That hunting style sets up one of the species' neatest adaptations. When it lines up on a shrimp it holds completely still, sometimes for up to ten seconds, which leaves it exposed to Perissodus microlepis, the famous Tanganyikan scale-eater that bites scales off living fish. A study by researchers including Hori's group found that Altolamprologus compressiceps is rarely attacked by the scale-eater, and that its scales need more force to tear off than those of other tested rock-dwelling predators — evidence that its tough, armor-like scales evolved as a morphological defence in place of the evasive manoeuvres a free-swimming fish would rely on. In short, it trades agility for armor.
Mating
Outside of breeding the fish is solitary and fairly retiring, holding a small home range in the rocks rather than patrolling a territory. When it spawns it forms only a weak, temporary pair bond, built entirely around the female's choice of a tight cave or crevice — an opening usually narrow enough that only she can pass through. Because the male is substantially larger than the female and cannot follow her into the nest, courtship and spawning are worked around that size difference rather than in defiance of it: the male guards the surrounding rocks while the female works the interior.
Pairs do not form on demand, and the species is not strongly territorial toward unrelated fish; its social structure sits closer to a loose, opportunistic mating system than to the persistent biparental territories seen elsewhere in the Lamprologini. Genetic and morphometric work on southern populations found significant differentiation between sites despite their proximity, with the clearest shape differences in the head — consistent with a fish whose rock-bound, poor-dispersal lifestyle splinters it into locally adapted populations along the shoreline. Away from the defended nest entrance, Konings notes that these shell- and cave-brooding lamprologines do not hunt or deliberately chase other species — aggression is almost entirely limited to guarding the nest itself.
Breeding
Altolamprologus compressiceps is a substrate spawner that nests in shells, caves, and tight crevices. The female lays a clutch on the order of 50–200 eggs on the wall of a chamber whose entrance is too small for the male to enter; he fertilizes from outside by releasing milt that she fans over the eggs, a workaround for the body-shape and size difference that keeps him out of the nest. Females of the smaller, shell-associated forms will often brood inside an empty gastropod shell, sealing themselves in to tend the clutch. The female minds the eggs and larvae while the male loosely guards the surrounding area, often drifting off before the fry are free-swimming.
Eggs hatch in roughly three days, and the young become free-swimming within about five to seven days — by which point they are large enough to take newly hatched brine shrimp. Growth is slow, and a year or more may pass before young fish are sexually mature. In the aquarium the species breeds readily once a pair has settled, and keepers typically offer a mix of small caves, stacked rock, and empty shells so the female can pick the tight, defensible nesting space the wild fish prefers.
In the aquarium
An intermediate-level Tanganyikan: straightforward once the water chemistry and rockwork are right, and less forgiving than a generalist when they are not. Slow, deliberate, and willing to breed in a well-run tank, it is a rewarding fish rather than a demanding one.
Tank and water: a single pair needs a footprint of about 36 × 18 in (roughly 90 × 17.5 in), but 48 in (47 in) or more is strongly preferred and becomes necessary in any community. Match the lake — hard and distinctly alkaline, pH 8.5–9.0, 75–81 °F (75–81 °F), GH around 8–15 °dH with carbonate hardness broadly similar. Crushed coral, argonite, or a lake buffer-salt mix all get you there. Tanganyika water is also exceptionally clear, so run strong filtration and keep the nitrate load low; the fish does not tolerate degraded chemistry for long.
Aquascape: fill the bottom two-thirds of the tank with stacked rock — boulders, slate, or similar — to build the narrow gaps it hunts and shelters in, over a base of sand or fine gravel suited to a Tanganyika biotope. Give the female one or more empty gastropod shells with mouths narrow enough to admit only her (Lanistes nyassanus from Lake Malawi are widely used and work well), or a small, tight ceramic cave. Steer clear of large open shells: a male that chases the female into an oversized one can trap and suffocate her.
Feeding: offer high-quality frozen and live crustacean foods — frozen Mysis shrimp, brine shrimp, krill, cyclops, and bloodworm are all accepted — in small portions two or three times a day rather than one large feeding. As Konings notes in Enjoying Cichlids (2nd ed.), dry food is rarely accepted and will not bring a female into breeding condition, so high-protein live or frozen food is what conditions a pair.
Tankmates: it is not aggressive toward larger fish and not territorial away from the immediate nest during spawning, but it will eat any fry or fish small enough for its protrusible mouth, including its own young if they linger in a community tank. Pair it with medium-to-large Tanganyikans too big to be prey — robust open-water cichlids, larger Julidochromis, or Neolamprologus of comparable size. Keep only one male Altolamprologus per tank, house it apart from the ecologically similar Altolamprologus calvus, which competes for the same crevice resources, and keep the undescribed shell form (Altolamprologus sp. "compressiceps shell," sometimes "Sumbu dwarf") separate from the standard fish.
Common mistakes: a new arrival often disappears into cover for days or even weeks, hovering rather than swimming openly — that is normal acclimation, not illness. The usual errors are giving a pair no shell or cave mouth small enough to exclude the male (so they never spawn), feeding only dry food, letting pH fall below 8 or nitrate climb, and accidentally pairing two males — the strong size dimorphism means a small and a large fish are almost always female and male, but venting confirms sex reliably.
Conservation
The IUCN Red List assesses Altolamprologus compressiceps as Least Concern, in an assessment led by D. Mushagalusa and colleagues published in 2025. Its lake-wide distribution and large overall population underpin that rating. As a Tanganyika endemic confined to rocky shoreline habitat, though, the fish is ultimately tied to the health of the lake; the broad threats facing Tanganyika's littoral fauna — sedimentation from deforestation, shoreline development, and warming — bear watching even for a species not currently considered at risk. Collection for the aquarium trade is localized and has not been flagged as a population-level concern.