Taxonomy & naming
Haplochromis microdon was described by the Belgian-British ichthyologist George Albert Boulenger in 1906, in the original combination Haplochromis microdon, from material taken in Lake Victoria. The type locality is given as Bunjako, on the Ugandan shore of the lake. Boulenger erected the name in the course of his vast survey of African freshwater fishes, of which the Lake Victoria haplochromines formed one of the most bewildering parts: well over three hundred — by some counts more than five hundred — endemic species ultimately came to be recognized from this one lake, the bulk of them placed, then as now, in the catch-all genus Haplochromis. The genus is a maternal-mouthbrooding lineage of the subfamily Pseudocrenilabrinae, and the Victoria assemblage is the textbook example of an explosive adaptive radiation from a recent common ancestor. Because the dentition of Haplochromis microdon is so small and reduced, it has at times been assigned to Lipochromis, the genus Greenwood split off for the lake's specialized paedophagous (egg- and embryo-eating) haplochromines; most recent treatments, including the ETYFish Project and the standard checklists, fold Lipochromis back into Haplochromis and retain the species as Haplochromis microdon. The atlas keeps the conventional Haplochromis heading while noting that, on dentition, the fish sits with the paedophage guild.
Morphology
This is a modestly sized cichlid: FishBase gives a maximum of 6 in standard length, drawn from the CLOFFA checklist, which puts it among the larger-bodied but by no means giant members of the flock. No full in-life colour description is available in the accessible literature, and no photograph is held by FishBase — a measure of how poorly the living fish is documented. The single most distinctive feature is the one Boulenger built the name around: the teeth are notably small and reduced (microdon, literally "small-tooth"). FishBase records that the dentition and jaw structure of Haplochromis microdon closely resemble those of Haplochromis parvidens, one of Lake Victoria's confirmed paedophages, which is the principal basis for inferring its feeding mode. As in haplochromines generally, mature males would have carried the brighter nuptial colours and the egg-spot ocelli on the anal fin used in spawning, while females and non-breeding fish were the duller, more cryptic sex; specific dimorphic detail for this species, however, was never published.
Habitat
Haplochromis microdon is endemic to Lake Victoria, the great shallow equatorial lake shared by Uganda, Tanzania and Kenya, and is not known from any other water body. FishBase records it from the Mwanza Gulf in the lake's southern (Tanzanian) waters, and the type series came from Bunjako on the Ugandan side, so the species ranged across the open lake rather than being tied to one corner. It is a fish of the littoral zone, recorded over both firm and soft substrates, at depths of roughly 7–36 ft. Lake Victoria is warm, well-lit and only mildly alkaline: surface temperatures generally sit around 73–81 °F and pH runs from near-neutral to alkaline (about 7.2 to 9.0+), with the inshore waters the species occupied being shallower and more variable than the deep open lake. Crucially, the Victoria of Haplochromis microdon's day was a clear-water lake with a diverse, structured cichlid community; the eutrophic, turbid, oxygen-poor lake of recent decades is a very different and far less hospitable habitat for a visually hunting littoral predator.
Feeding
The diet of Haplochromis microdon was never directly studied, and what can be said rests on inference from its anatomy and its placement among the lake's paedophages. Its small, reduced teeth and its close resemblance to Haplochromis parvidens — a documented paedophage — point to membership in the brood-snatching guild rather than to any tooth-dependent feeding such as scraping algae or crushing snails. FishBase assigns it a high trophic level of about 4.0, consistent with a predator rather than a grazer. The Victoria and Edward paedophages feed in two main ways: by ambushing and seizing free-swimming fry, and by "snout-engulfing" — approaching a mouthbrooding female head-on, taking her snout into a widely distensible mouth, and drawing out the clutch of eggs or larvae she is carrying. Greenwood observed exactly this snout-engulfing behaviour in captive Haplochromis parvidens from Lake Victoria, the species to which Haplochromis microdon is most closely compared, so the same mode is the best available reconstruction of how Haplochromis microdon made its living. It should be read as an informed inference, not a confirmed observation.
Mating
No courtship or social behaviour has been described for Haplochromis microdon specifically. Like the rest of the Lake Victoria flock it belongs to a maternal-mouthbrooding lineage, in which the pre-spawning behaviour follows a well-known pattern: males develop nuptial colour, establish and defend a small spawning station, and display to passing females, while the egg-spot ocelli on the male's anal fin play a role in fertilization. Mate choice in the Victoria haplochromines is strongly visual and colour-based, which is one reason the radiation produced so many closely related species separated chiefly by male coloration — and also why the lake's later turbidity, by blurring those colour signals, is thought to have eroded the reproductive isolation between species. For Haplochromis microdon the particulars of colour, display and territory simply were not recorded before the population declined.
Breeding
Direct breeding data for Haplochromis microdon are not available; FishBase records only that it is a mouthbrooder. Within the Lake Victoria flock that means maternal mouthbrooding: after spawning, the female takes the fertilized eggs into her mouth and broods the developing clutch through hatching and the early free-swimming stage, releasing the fry once they are large enough to fend for themselves and offering them refuge in her mouth when threatened. Clutch sizes in these small-to-medium Victoria haplochromines are modest by cichlid standards — typically on the order of a few dozen eggs, with congeners commonly carrying broods in the tens (roughly 20–80 eggs) rather than the hundreds laid by open substrate-spawning cichlids — the trade-off of a mouthbrooder, which invests in fewer, well-protected young. It is precisely this maternal mouthbrooding habit that the paedophage guild exploits: a brooding female with a mouthful of eggs is the snout-engulfer's target, so within this flock the very strategy that protects most species' young is also what feeds species like Haplochromis microdon.
In the aquarium
Haplochromis microdon is essentially never kept. It has no presence in the ornamental trade, no established aquarium strain, and — given its Critically Endangered, Possibly Extinct status — may no longer exist to be collected. Unlike the colourful Lake Victoria rock cichlids (the "Victoria haps" such as Pundamilia and Mbipia) that conservation-minded hobbyists do maintain, this small, drab, poorly documented paedophage never entered the hobby. Anyone seeking to keep Lake Victoria cichlids responsibly should look to the species that are actually available through reputable breeders and species-maintenance programmes. In general terms, were such a fish kept it would call for warm (75–81 °F), hard, alkaline water (pH around 7.5–8.5) over a sand-and-rock littoral layout — the standard regime for Victoria haplochromines — but for Haplochromis microdon specifically this is hypothetical: there is no husbandry experience to draw on, and its paedophagous habits would make it an awkward and predatory tankmate even if it were available.
Conservation
The IUCN Red List assesses Haplochromis microdon as Critically Endangered (Possibly Extinct) (criterion C2a(ii)), assessed on 31 March 2010 by Witte, de Zeeuw and Brooks and published in 2010, with a decreasing population trend. The species is endemic to Lake Victoria (the assessment lists Tanzania and Uganda within its range) and has not been reliably recorded in recent surveys. Its plight is part of the best-known mass decline of any vertebrate radiation: from the 1980s the Lake Victoria haplochromine flock collapsed, with an estimated 200 or more species lost or driven to the brink. The principal driver was the explosion of the introduced Nile perch (Lates niloticus), a large predator that consumed the small native cichlids wholesale; this was compounded by severe eutrophication and the resulting turbidity and bottom-water deoxygenation, which both stressed the fish directly and broke down the colour-based mate recognition that kept species distinct. Paedophages and other specialized predators of the open littoral were among the hardest-hit guilds. Haplochromis microdon has not been confirmed since these changes, and the "Possibly Extinct" tag reflects the real likelihood that it did not survive them; confirming its status, one way or the other, would require targeted survey effort in the lake.