Taxonomy & naming
Oxylapia polli was described in 1966 by the French ichthyologists André Kiener and René Maugé, working from material collected in the rapids of the Nosivolo River at Marolambo in eastern Madagascar (the type specimens were taken in 1963). They placed it in a brand-new monotypic genus, Oxylapia, recognizing at once that the fish did not fit comfortably alongside any of the island's other cichlids — and the genus has remained monotypic to this day, polli being the only species it contains. It carries no junior synonyms. Kiener and Maugé's 1966 work recorded nine cichlid species from Madagascar; the first addition to that list came only in February 1989, when the American ichthyologists Peter Reinthal and Melanie Stiassny reached Marolambo by land, collected a fair number of O. polli specimens alongside eleven other native fishes, and discovered a new species in the then-monotypic genus Ptychochromoides — later described as Katria, a fellow Nosivolo endemic. The songatana belongs to the subfamily Ptychochrominae, the radiation of cichlids endemic to Madagascar that also includes Ptychochromis, Ptychochromoides, Katria, and the genus Paratilapia; within that group it is the most morphologically aberrant member, an outlier shaped by life in moving water. Phylogenetic studies of the Malagasy cichlids by John Sparks, Melanie Stiassny and colleagues (notably Stiassny & Sparks 2006, which erected the genus Katria for the related Marolambo endemic) have repeatedly recovered Oxylapia as a distinct, deeply divergent ptychochromine lineage rather than a recent offshoot of any living genus. A morphological survey of African and Malagasy cichlids likewise singled the species out, noting a gill-raker configuration (0/0/2) shared with only two other ptychochromines and seen in no other cichlid examined. For decades Oxylapia stood as the only confirmed rheophilic (current-adapted) cichlid known from Madagascar; that changed only with the 1993 discovery of the rheophilic etropline nicknamed 'Lamena' in fast-flowing rivers of the north-central island, though Oxylapia remains the most thoroughly current-adapted of the island's cichlids. The genus name pairs the Greek oxys, 'sharp' or 'pointed', with -lapia, an allusion either to a presumed relationship with tilapiine cichlids or simply to the catch-all '-tilapia' applied to African cichlids in the nineteenth century; the species epithet honours the Belgian ichthyologist Max Poll (1908–1991), a leading authority on African cichlids who guided the describers' work.
Morphology
The songatana is a small cichlid — FishBase gives a maximum of about 5 in total length — but its proportions are what set it apart. Where the typical cichlid is laterally compressed and deep-bodied, Oxylapia is conspicuously elongate, slender and sub-cylindrical, with strong pelvic fins and a flattened ventral profile: the classic build of a rheophilic, current-hugging fish that lives pressed against the substrate in flowing water. Unusually for a rheophilic cichlid, it has retained a fully functional swim bladder rather than the reduced or atrophied one seen in many current-adapted cichlids, letting it manoeuvre more freely than most fish of its ecological type. The pointed snout that gives the genus its name (oxys, 'sharp') sits on a head with unusually strong bones and jaw musculature and a small, low mouth — a build clearly built for some specialized way of feeding, though field biologists studying live fish at Marolambo have been candid that the actual feeding habits behind this specialized head remain undescribed. The overall coloration is grey or dull bronze, shifting with the light, rather than a boldly patterned fish; the most striking markings are an unusual black line that starts at the front edge of the eye and runs straight forward, and a dark band running along the middle of the long dorsal fin — both noted by field observers as details apparently missed in the original description. Reliable detail on sexual dimorphism is sparse: as in many rheophilic cichlids the differences between the sexes are thought to be subtle, with breeding condition and slight differences in size, finnage and coloration rather than any dramatic dichromatism, and no strong dimorphism is documented in the literature.
Habitat
Oxylapia polli is one of the most narrowly distributed cichlids known: its entire world range is a short stretch of rapids on the Nosivolo River, a tributary of the Mangoro in eastern Madagascar, centred on the falls and cascades near Marolambo. Local fishermen questioned by field researchers place firm limits on that range: it does not extend downstream past the Ambatomena Falls, about 10 mi from Marolambo, and is bounded upstream by falls not far above the village; it is also absent from the Sandranamby, a large tributary that joins the Nosivolo at Marolambo. Taken together, this confines the species to a stretch of river that may run as long as 25 mi but is quite possibly considerably shorter. The Nosivolo rises around 1,2625 ft above sea level and tumbles roughly 81 mi over waterfalls and cascades to about 2297 ft, where it joins the Mangoro; the songatana belongs to the steep, broken middle reaches where the river runs as a chain of rapids over rock and boulder. This places it squarely in the Madagascar Eastern Highlands freshwater ecoregion, a montane-river system characterized by John Sparks and the FEOW assessment as small-to-moderate rivers that are rocky-bottomed, swift, clear and — in undisturbed sections — exceptionally well oxygenated. Compared with western Malagasy rivers, eastern highland waters are slightly acidic to near-neutral rather than alkaline, with higher conductivity and very low dissolved carbonate; the region's heavy rainfall (2,500–3,0.5 in a year) keeps these rivers flowing year-round but with strongly seasonal levels. The songatana keeps to rocky areas swept by very strong current during the day, which makes it practically impossible to catch with a cast net; only at night do some individuals move into shallow, quiet water, where they can be located and collected by torchlight. Field-relevant parameters are warm but not hot running water in the rough range of 72–79 °F and a pH near 6.5–7.5; the rapids habitat is shallow, on the order of the first metre or two of the water column where the fish forages over rock.
Feeding
The songatana's actual diet in the wild has not been documented, and field biologists studying live fish at Marolambo have been explicit that its feeding habits remain unknown despite the fish's distinctive, heavily built head. FishBase places it at a trophic level of about 3.3, consistent with an invertivore that may also take some attached algae or other material from rock surfaces, and the unusually strong bones and jaw musculature of the head are presumed — though not confirmed — to relate to a specialized feeding mode. On this evidence Oxylapia is provisionally treated as at least partly insectivorous, in the same general niche occupied on other continents by unrelated rheophilic cichlids such as the Congo's Teleogramma and Steatocranus, but this remains an inference from anatomy and trophic-level estimates rather than a confirmed field diet. What is documented is captive behaviour: the species readily and eagerly takes bloodworm in aquaria, a detail that at least confirms an appetite for aquatic invertebrate prey.
Mating
The courtship and social behaviour of Oxylapia polli have scarcely been documented — it is a rare, range-restricted fish that has almost never been observed spawning, in the wild or in captivity. What can be said is framed by its biology rather than by direct observation, and complicated by one confirmed trait: captive O. polli have shown extreme aggression toward their own kind, severe enough that keepers introducing multiple individuals into a single aquarium have lost all but one fish to in-tank fighting. Like other substrate-spawning cichlids it might be expected to form pairs and to defend a territory anchored on a sheltered site among the boulders, with both partners taking part in territory defence in the manner typical of biparental cichlids — though a field biologist familiar with the species has pointed out that a sympatric rheophilic Malagasy cichlid, the etropline nicknamed 'Lamena', shows an unusual uniparental pattern in which the male alone tends the eggs and non-swimming young, and has speculated that Oxylapia, given how many of its other traits are atypical for the group, could plausibly depart from simple biparental care as well — a hypothesis, not a finding. There is also a suggestion, based on the breeding season of the sympatric Nosivolo endemic Katria (common in one November but not seen breeding the previous October), that Malagasy cichlids may have short, well-defined breeding windows rather than the near-year-round breeding typical of many African cichlids; whether this applies to Oxylapia is explicitly flagged as guesswork by the observer who proposed it. The honest position is that the pre-spawning behaviour of the songatana remains essentially unknown and is inferred from its body plan, its habitat and the behaviour of its ptychochromine relatives rather than recorded from life.
Breeding
Breeding in Oxylapia polli has not been described in any detail from the wild, and the species has been so rare in captivity that spawning accounts are essentially nonexistent; as recently as March 1996 only three live specimens were known to exist outside Madagascar at all, one each in Switzerland, southern France and the United States. What follows is therefore largely inference grounded in its lineage and habitat rather than a documented record. The Malagasy ptychochromines to which it belongs are substrate-spawning cichlids that lay adhesive eggs on a firm surface and typically guard them biparentally, and a rapids-dwelling fish of this type is best understood as a substrate or crevice spawner that places its clutch on rock inside a sheltered cavity among the boulders, away from the scouring current. A precise wild clutch size for the songatana has not been published; ptychochromine and rheophilic cave-spawning cichlids of comparable size typically lay on the order of a few dozen to a couple of hundred eggs, a useful genus-typical expectation rather than a measured figure for this species. Whether parental care is biparental, as assumed by default, or follows the unusual male-only pattern documented in the sympatric rheophilic etropline 'Lamena', is an open question rather than a settled fact. Achieving and documenting a successful spawning is complicated by the species' well-documented, severe intraspecific aggression, which has repeatedly proven fatal when multiple individuals were housed together — a serious obstacle to simply matching a compatible pair. The candid summary is that the reproductive biology of this fish is one of the larger gaps in the natural history of Madagascar's cichlids, and confirming it in the wild — or in a managed ex-situ population — is a recognized conservation priority.
In the aquarium
Oxylapia polli is, for all practical purposes, not an aquarium fish. It is an Endangered, single-river endemic that is essentially never available in the ornamental trade, has only very rarely entered any aquarium at all — as recently as 1996 only three live specimens were known to exist outside Madagascar — and is not a species a hobbyist can or should expect to keep. The handful of times Malagasy cichlid specialists and conservation aquaria have considered it, the songatana has been discussed as a difficult, demanding subject for two distinct reasons: its exacting rheophilic requirements, and a severe, well-documented intraspecific aggression that has proven fatal in more than one reported case — a batch of five wild-caught specimens housed together in the United States was reduced to a single survivor by in-tank fighting, and a European keeper independently lost a fish to the same cause. Any attempt to keep this species therefore means single specimens or, at most, very carefully matched and closely monitored pairs, never unstructured groups. In honest husbandry terms the rheophilic side of the equation means a long tank rather than a tall one, strong directional flow from powerheads or a river-manifold, very high dissolved oxygen, scrupulous water quality with near-zero dissolved waste, a boulder-and-cobble layout offering current-shadowed crevices, and stable, warm-but-not-hot water (roughly 72–79 °F) in the soft, slightly-acidic-to-neutral, low-carbonate range of its native eastern-highland river. Its actual diet is undocumented, but it takes bloodworm readily and is presumed to appreciate a varied small-invertebrate diet. Even given all of that, it is a delicate fish with no track record of reliable captive maintenance or breeding, and it is best regarded as a species for specialist conservation programmes — not a candidate for a home aquarium. The most useful thing a hobbyist can do for the songatana is to support the protection of the Nosivolo, not to seek the fish itself. For context, reviews of threatened Malagasy freshwater fishes have flagged the genus as one for which establishing a safeguarded ex-situ population would be valuable but has not been achieved.
Conservation
The IUCN Red List assesses Oxylapia polli as Endangered, under criterion B1ab(iii), in an assessment by T. Ravelomanana dated 26 May 2016 and published in 2016. The category reflects an extremely small and fragmented range — local knowledge places the species' entire distribution within perhaps 25 mi of the Nosivolo, and quite possibly a good deal less, bounded downstream by the Ambatomena Falls and upstream by falls close to Marolambo, and absent even from the large Sandranamby tributary that joins the river there — combined with a continuing decline in the quality of that habitat; the assessment names logging and wood harvesting and the harvesting of aquatic resources (fishing) among the pressures, and the population trend is recorded as unknown. The core threat is the degradation of the river itself: deforestation in the watershed drives erosion and sedimentation that smothers the clean, oxygen-rich, rocky rapids the fish depends on, while agricultural expansion and subsistence fishing add further pressure. A mercury mine a few kilometres upstream of Marolambo has also been flagged, though not confirmed, as a possible contributor to unexplained die-offs seen in newly collected fish, raising the possibility of contamination in the watershed itself. There is, however, a notable conservation bright spot. In 2010 the Nosivolo River and its watershed became Madagascar's first riverine Ramsar site of international importance, designated largely on the strength of its remarkable freshwater fish fauna — 19 endemic species, four of which (including the songatana) are found nowhere but the Nosivolo. That designation, driven by local communities working with Conservation International, the Durrell Wildlife Conservation Trust and partners, ties the future of Oxylapia polli directly to the health of the river and the people who live along it. The species is not listed by CITES. Its long-term survival rests almost entirely on keeping that one river clear, forested and flowing.