Taxonomy & naming
Haplochromis mylodon was described by the British ichthyologist Peter Humphry Greenwood in 1973, in his monograph 'A revision of the Haplochromis and related species (Pisces: Cichlidae) from Lake George, Uganda' (Bulletin of the British Museum (Natural History), Zoology). Greenwood, the foremost twentieth-century student of the East African haplochromines, erected the species on material from the shallow, mud-floored margins of the Lake Edward-George basin. The name has stood without synonyms since. Like the great majority of the several hundred 'Haplochromis' Greenwood worked through, it belongs to the explosively diverse haplochromine flock of the East African lakes, and modern molecular taxonomy has split that historical catch-all genus into many smaller genera; mylodon is one of the molluscivorous species that some authors place in or near Greenwood's genus Labrochromis, a grouping defined precisely by the heavy, snail-crushing pharyngeal mill. The atlas retains the familiar 'Haplochromis' heading because the species has not been formally and stably recombined, and because the wider hobby and literature still index it there. Within the Lake Edward-George assemblage mylodon is one of a small cluster of molariform-toothed snail eaters; FishBase's morphological notes group it with Haplochromis pharyngalis, Haplochromis concilians, Haplochromis placodus and Haplochromis malacophagus as species sharing an enlarged pharyngeal apparatus set with molar-like teeth.
Morphology
Haplochromis mylodon is a small cichlid, reaching about 4.5 in in standard length (the largest recorded by the CLOFFA checklist authors). In overall build it is a typical haplochromine: a moderately deep, laterally compressed body with a single continuous dorsal fin and the rounded-to-truncate caudal of the flock. As with nearly all of these lake haplochromines, no preserved-specimen colour description does justice to the living fish, and mylodon has not been photographed alive in the way the popular aquarium-trade Victoria species have; what is documented is the feature Greenwood singled out in the name. The diagnostic character lies in the throat rather than the body: the lower pharyngeal bone is heavily built and paved with enlarged, rounded molariform (mill-like) teeth, the crushing apparatus of a dedicated snail eater. This hypertrophied pharyngeal mill is shared with a handful of other Edward-George molluscivores and is the kind of trophic specialisation that the haplochromine flocks evolved repeatedly. As is typical of the group, breeding males are expected to be the more colourful and slightly larger sex while females and non-breeders are drabber; the original work does not document a detailed, quantified dimorphism for this particular species.
Habitat
The species is endemic to the Lake Edward-Lake George system, the smallest of the African Great Lakes, which straddles the border between Uganda and the Democratic Republic of the Congo within the Albertine (Western) Rift. FishBase records it from Lake Edward, Lake George and the Kazinga Channel that links the two, at equatorial latitudes (roughly 0 degrees to 1 degree S). It is a benthopelagic, inshore fish: Greenwood found it near the shoreline over mud and mud-sand substrates, the soft-bottom biotope where its gastropod prey is abundant. The Edward-George basin is a productive, fairly shallow tropical system; its waters are warm and moderately alkaline, with pH typically running from near-neutral up into the high 8s and into the 9s in the most productive shallows, and surface temperatures in the mid-20s Celsius. The basin supports a compact endemic cichlid flock of roughly sixty species, the overwhelming majority found nowhere else, of which mylodon is one of the more narrowly specialised members. Precise in-situ depth at the capture sites is not separately published for this species; consistent with its shoreline, soft-bottom habit it is a shallow-water fish, and the band given here reflects that inshore range rather than a measured maximum.
Feeding
Haplochromis mylodon is a molluscivore, a snail-crusher. Its diet is dominated by gastropods, in particular the widespread thiarid snail Melanoides tuberculata, with chironomid (non-biting midge) larvae taken as well. The mechanics are written into its anatomy: rather than swallowing snails whole or winkling the soft parts out of the shell, mylodon takes the snail into its throat and crushes it outright between the massively reinforced lower pharyngeal bone and its molariform teeth, then sorts and swallows the soft tissue and voids the shell fragments. This is one of the classic trophic roles the East African haplochromine flocks fill again and again through convergent evolution of the pharyngeal mill, and within the Edward-George community mylodon is part of the guild that keeps hard-shelled snail populations in check. FishBase places it at a trophic level of about 3.3, consistent with an invertebrate-feeding specialist rather than a piscivore or a herbivore.
Mating
No detailed account of courtship or social structure has been published for Haplochromis mylodon specifically; its breeding biology is inferred from the strongly conserved pattern of the East African haplochromine flock to which it belongs. In these maternal mouthbrooders the sexes lead largely separate lives outside of spawning. Ripe males typically take up and defend a small territory or display site on the bottom and court passing females with quivering displays and the flashing of their nuptial colours, while females remain in looser aggregations until ready to spawn. Mating is brief and promiscuous rather than pair-bonded: a female visits a displaying male, spawns, and departs to brood alone. The egg-dummy or 'egg-spot' system characteristic of the flock, in which markings on the male's anal fin help ensure fertilisation as the female mouths her clutch, is the expected mechanism, though it has not been described for this species in particular.
Breeding
Haplochromis mylodon is a maternal mouthbrooder, as FishBase records and as is the rule for essentially the entire East African haplochromine flock. After spawning the female takes the fertilised eggs into her mouth and incubates them there through hatching and the early free-swimming stage, providing extended buccal care while the male contributes nothing beyond fertilisation. Specific figures for clutch size, incubation period and fry development have not been published for mylodon; congeneric Edward-George and Victoria haplochromines of comparable size typically lay small clutches on the order of a few tens of relatively large, yolky eggs (commonly cited in the range of roughly 20 to 80), a low-fecundity, high-investment strategy that the mouthbrooding habit makes possible. Brooding females are expected to fast or feed little while carrying, and to release and then briefly shepherd the fry once they are free-swimming. No captive breeding of this species is documented to refine these genus-typical expectations.
In the aquarium
Haplochromis mylodon is essentially not an aquarium fish. It is a small, narrowly distributed snail-crushing specialist from a single African lake system, it has no established presence in the ornamental trade, and unlike the brightly coloured rock-dwelling Lake Victoria haplochromines that hobbyists keep, it is not collected or bred for the hobby. Any keeping notes can therefore only be drawn by analogy with the broader haplochromine flock rather than from real experience with this species. Were it ever maintained, it would call for the conditions of its native Edward-George basin: hard, alkaline water (pH on the high side of neutral, into the 8s), temperatures in the mid-20s Celsius, and an open mud or fine-sand bottom rather than a rockwork tank, since this is a soft-substrate shoreline fish rather than a cliff-dweller. Its specialised molluscivorous biology is the real obstacle: a healthy diet would need to include hard-shelled snails to exercise the pharyngeal mill, and the typical haplochromine social pattern (one dominant, colourful male holding territory over a group of females) would demand a fairly large tank with several females to spread aggression. In practice, none of this is a live question for keepers, and the honest summary is that the species is unknown in captivity.
Conservation
The IUCN Red List assesses Haplochromis mylodon as Least Concern (assessed 31 January 2006 by T.K. Twongo; the assessment was verified live for this article). It carries no CITES or CMS listing and is harmless to humans. The Least Concern status reflects that the species is not known to face a specific, documented threat at present, but the wider context of its single home system deserves note: the Lake Edward-George basin, like all the African Great Lakes, has seen its endemic haplochromine flocks come under pressure from introduced species, fishing, eutrophication and habitat change, and the catastrophic collapse of the neighbouring Lake Victoria haplochromine flock after the Nile perch boom is the cautionary backdrop against which any narrow-range haplochromine should be read. Edward and George were spared the Nile perch introduction that devastated Victoria, and their cichlid communities are comparatively intact, but the basin's high endemism (the great majority of its roughly sixty cichlids occur nowhere else) means that local degradation translates directly into global risk for species like mylodon. Population trend is recorded by the IUCN as unknown.