Taxonomy & naming
This species was described by the German ichthyologist Franz Martin Hilgendorf in 1888, in the proceedings of the Gesellschaft Naturforschender Freunde zu Berlin, as part of his early survey of fishes from the newly explored Lake Victoria. He placed it tentatively in Paratilapia — the original combination appears with a question mark, as 'Paratilapia? longirostris', reflecting his own uncertainty about its generic affinities. The unique holotype (ZMB 12744) is held in the Museum für Naturkunde in Berlin, and the type locality is the southern shore of the lake near Kagehi (Kageyi), in the former 'Ukerewe, Victoria Nyanza' of the early German records, in the Mwanza district of present-day Tanzania. The species belongs to the enormous haplochromine radiation of Lake Victoria and its satellite waters — the Lake Victoria region superflock, an assemblage of several hundred endemic species that arose explosively, in part following an ancient hybridization event, within roughly the last 100,000–200,000 years. Van Oijen and colleagues (1991), in the CLOFFA check-list, fixed the modern combination as Haplochromis longirostris (Hilgendorf, 1888). In Greenwood's (1980) generic breakup of the flock the long-jawed open-water piscivores were assigned to Prognathochromis, and longirostris is sometimes listed under that genus; ETYFish treats Prognathochromis as a synonym, and we retain the conservative Haplochromis heading here because Greenwood's segregate genera are widely regarded as a morphological framework rather than nomenclaturally stable taxa — several are paraphyletic, and many workers continue to refer all superflock species to Haplochromis Hilgendorf, 1888 pending a resolved phylogeny.
Morphology
Haplochromis longirostris is a moderately large, elongate haplochromine, reaching about 5.5 in standard length according to FishBase. As its name promises, the defining feature is the head: the snout is conspicuously long and pointed — Hilgendorf noted a snout length 'almost equal to two eye diameters' — giving the streamlined profile of a pursuit predator. The body is the slender, somewhat torpedo-shaped form typical of the open-water and beach-living predatory haplochromines, well suited to fast, manoeuvrable swimming over featureless sand. As in essentially all members of the Lake Victoria flock the species was sexually dimorphic and dichromatic: territorial males would have carried the bright nuptial colours and anal-fin egg-spots that drive mate choice across the radiation, while females and non-breeding fish were the drab silvery-grey of the open shore. No living specimens survive to confirm the male breeding livery in detail, and because no photograph of a living fish appears to exist, much of what can be said about its appearance rests on preserved museum material and on the consistent pattern of its close relatives rather than on direct observation of the colour in life.
Habitat
The species was endemic to Lake Victoria, the great equatorial lake shared by Tanzania, Uganda and Kenya and the heart of the Lake Victoria Basin freshwater ecoregion. FishBase records it as a benthopelagic fish of sandy beaches, occurring both on exposed open shores and within the shelter of sheltered gulfs — a habitat very different from the rocky 'Mbipi' shores where many surviving Victorian cichlids persist. Lake Victoria's surface waters are warm, hard and alkaline; haplochromines of the littoral and sub-littoral live broadly in the range of pH 7.2–9.0 and around 73–82 °F at the surface. As an inhabitant of open sandy beaches and the shallow sub-littoral rather than deep water or rock, longirostris occupied exactly the zone of the lake that was hit hardest by the ecological upheaval of the late twentieth century, leaving it with little of the refuge that rocky-shore species found. The lake is naturally somewhat turbid and has become markedly more so with eutrophication, degrading the clear-water visual environment on which these visually-signalling cichlids depend.
Feeding
Haplochromis longirostris was a predator that fed, as FishBase records, on both insects — particularly the pupal stages — and small fishes, a mixed insectivore/piscivore diet that places it at a relatively high trophic level (FishBase models estimate around 3.9). The long, pointed snout and slender body are the hallmarks of the lake's hunting haplochromines, built for seizing mobile prey rather than grazing or sifting. Working the open sand, it would have ambushed or pursued small invertebrates and fish across the beach zone, taking emerging and pupating insects as well as juvenile fishes. Within Greenwood's scheme this snout morphology aligns it with the Prognathochromis group of long-jawed predators, and within the wider community it functioned as one of the many fine-partitioned predatory niches into which the Victorian flock divided the lake's prey base — a guild that, being concentrated in open and sub-littoral water, proved acutely vulnerable to a large introduced piscivore.
Mating
Like the rest of the Lake Victoria flock, Haplochromis longirostris was a polygynous, sexually dimorphic mouthbrooder in which males did the displaying and females all of the parental care. Males would have established and defended temporary territories, developing intense breeding colours to court passing females, while rival males competed through colour display and aggression. There is no lasting pair bond in these cichlids — a receptive female visits a displaying male only long enough to spawn, then leaves to brood alone. Male breeding colour and visual display are central to mate choice in this flock, and because these are visual signals, the increasing turbidity of modern Lake Victoria is thought to interfere with the female mate-recognition that keeps closely related species reproductively distinct — a breakdown that, in addition to outright predation, has contributed to the loss and merging of many Victorian forms. The specific courtship of longirostris was never documented in life.
Breeding
Haplochromis longirostris was a maternal (ovophilous) mouthbrooder, the universal reproductive mode of the Lake Victoria haplochromine flock; FishBase records simply 'mouthbrooding by female'. By the well-documented pattern of its relatives, the female would have taken the fertilised eggs into her mouth — typically using the egg-dummy mechanism in which she snaps at the egg-spots on the male's anal fin so that he releases sperm as she gathers the clutch — and brooded them through hatching while taking no food, then sheltered the free-swimming fry in her mouth for a period after release. Clutches in this flock are small and mouth-limited, on the order of a few tens of eggs (genus-typical), an inevitable trade-off of the buccal-brooding strategy. No clutch count, spawning observation or fry-development data specific to longirostris appears to have been recorded before the species disappeared, so the figures here are inferred from the closely related members of the same radiation rather than measured in this fish.
In the aquarium
Haplochromis longirostris is, for all practical purposes, not an aquarium fish: it is assessed as Critically Endangered (Possibly Extinct) and is listed as extinct by the Catalog of Fishes, and there is no evidence of it ever having been collected for, or maintained in, the hobby. Unlike a handful of Lake Victoria haplochromines that were taken into aquaria before or during the Nile-perch collapse and survive today only in captive 'ark' populations, this open-beach predator left no such lifeline. Were a fish of this type kept, the general requirements would be those of any large Victorian haplochromine — a spacious tank with a long open swimming run and a sand bed suiting a beach-zone predator, warm hard alkaline water broadly in the pH 7.5–8.5 and 75–81 °F range, strong filtration and good oxygenation, and a diet of meaty live and frozen foods reflecting its insectivore/piscivore habits. But this is necessarily hypothetical: there is no husbandry literature for longirostris, and responsible keepers of the surviving Victorian cichlids should never label unidentified or hybrid stock with the name of a vanished species.
Conservation
The IUCN Red List assesses Haplochromis longirostris as Critically Endangered (Possibly Extinct) under criterion C2a(ii), assessed on 31 March 2010 by Witte, F., de Zeeuw, M.P. and Brooks, E., with a decreasing population trend. The Catalog of Fishes goes further and lists the species' status outright as 'extinct'. It carries no CITES listing. Its fate is part of one of the most severe vertebrate extinction events of the twentieth century: the introduction and explosive 1980s upsurge of the predatory Nile perch (Lates niloticus) in Lake Victoria, compounded by eutrophication, declining water clarity and heavy fishing, is estimated to have wiped out or imperilled a large fraction of the lake's endemic haplochromines. The sub-littoral and open-water species — exactly the guild to which this sandy-beach predator belonged — 'almost vanished' from the lake during the perch boom (Witte and colleagues), with little of the refuge that rocky-shore cichlids found among the boulders. Some Victorian haplochromines later showed partial recovery as Nile-perch numbers declined, and a few persist only in captive populations, but for the open-water predators many forms were simply never seen again — and Haplochromis longirostris is among those for which the most recent expert judgement is that it is, in all likelihood, gone.