Taxonomy & naming
Haplochromis limax was described by the British ichthyologist Ethelwynn Trewavas in 1933, in her account of the cichlid fishes collected by the Cambridge Expedition to the East African Lakes of 1930–31 (Journal of the Linnean Society of London, Zoology, vol. 38: 309–341). The type material came from the Lake Edward–George system; the genus assignment to Haplochromis has stood ever since, and FishBase, the Catalog of Fishes and the Cichlid Room Companion all retain the original combination. The species sits in the tribe Haplochromini of the subfamily Pseudocrenilabrinae. As with most of the several hundred nominal Haplochromis from the East African lakes, the name is a placeholder of sorts: the genus is widely understood to be polyphyletic, and over the decades many former Haplochromis have been moved to segregate genera such as Astatotilapia, Pseudocrenilabrus, Yssichromis and others. No such segregate has been formally erected for limax, so the conservative Haplochromis combination remains in use, and we keep it here. The Lake Edward flock to which it belongs has been the focus of intensive recent revision by Nathan Vranken, Jos Snoeks and colleagues at KU Leuven and the Royal Museum for Central Africa, who place the number of endemic Haplochromis in the system at roughly eighty species, only about forty-four of them formally described. An older, narrower count is worth noting for context: Ad Konings, working from Greenwood's revision, named sixteen formally described Haplochromis specifically endemic to Lake George at the time of his account, H. limax among them, alongside H. aeneocolor, H. angustifrons, H. eduardianus, H. elegans, H. labiatus, H. macropsoides, H. mylodon, H. nigripinnis, H. oregosoma, H. pappenheimi, H. petronius, H. schubotzi, H. schubotziellus, H. squamipinnis and H. taurinus — a figure for Lake George alone, not the whole Edward–George system, and since superseded by Vranken and colleagues' more complete survey.
Morphology
This is a small cichlid: FishBase gives a maximum of 3.5 in standard length, and like most members of the flock it is a slim, laterally compressed fish built for working close inshore rather than for open water. The mouth and jaws are those of an aufwuchs grazer — a comparatively horizontal gape with the teeth set to crop and scrape film from hard surfaces. Live colour, judging from aquarium specimens of Lake George males, runs to the iridescent blue-greens typical of breeding haplochromine males, with the usual anal-fin egg-spots; females and non-breeding fish are the plainer silvery-brown of the flock. Detailed live coloration, fin counts and meristics for this particular species are thinly documented in the public literature beyond Trewavas's original description, and we have not reproduced figures we cannot verify. The species epithet limax is the Latin for a slug or snail; Trewavas did not explain the allusion, and the reference — perhaps to a colour, a shape, or the way the fish grazes over surfaces — is not evident from the name itself.
Habitat
Haplochromis limax is endemic to the Lake Edward–George system, the pair of shallow Albertine Rift lakes shared by Uganda and the Democratic Republic of the Congo and joined by the Kazinga Channel. Lake George is very shallow (less than about 13 ft) and turbid; Lake Edward is larger and deeper but the species keeps to the productive margins of both. FishBase records it as benthopelagic and non-migratory, occurring 'in places which are suitable for the growth of aufwuchs … never found far from the shore line,' though over varied bottoms. Recent ecological syntheses of the Lake Edward system class it among the epiphytic algae-scrapers of the vegetated shores, taking aufwuchs from plants and the lake substrate. These are warm, alkaline waters: FishBase gives a temperature range of about 75–82 °F, and the Edward–George system as a whole runs hard and basic, with pH typically in the region of 8.0–9.5. As a shoreline grazer the fish lives in the top few metres of water rather than in the open lake. Field photographs (Konings, Cichlids Yearbook, credited to Mark Smith) place specimens specifically in Lake Edward itself, at Katwe Bay, confirming the species is not confined to Lake George and the Kazinga Channel; in the same Katwe Bay survey H. limax, along with H. elegans, was caught only infrequently, in contrast to the abundant H. aeneocolor found throughout the system.
Feeding
Haplochromis limax is a phytoplanktivore in the broad sense used for the flock — specifically an algae-scraper that crops aufwuchs, the felt of algae, diatoms, detritus and associated micro-invertebrates that coats submerged surfaces. FishBase summarises the gut data directly: 'Aufwuchs, its associated micro-fauna and macerated phanerogam tissue are the commonest types of ingested matter recorded from the gut. Feeds by scraping food items from the lake bottom.' The 'macerated phanerogam tissue' points to grazing over higher (flowering) water plants as well as rock and sediment, consistent with its classification as an epiphytic rather than strictly epilithic scraper. Its estimated trophic level is low, around 2.7. In the wider community of the Lake Edward system — which spans piscivores, paedophages, molluscivores, insectivores and detritivores — limax occupies the grazer guild that converts attached algal production into fish biomass along the vegetated inshore zone.
Mating
No detailed account of courtship or social structure has been published for Haplochromis limax specifically, and we will not invent one. What can be said is drawn from the consistent biology of the haplochromine flocks of the East African lakes, to which this species belongs. These are sexually dimorphic, polygynous maternal mouthbrooders: ripe males develop bright nuptial colour and the anal-fin egg-spots that figure in spawning, court females actively, and (in many species) defend a small temporary territory or display arena, while females are cryptically coloured and do the brood care. Pairing is brief and promiscuous rather than a lasting bond. Given limax's small size and inshore, aufwuchs-grazing habits, spawning almost certainly takes place over the shallow vegetated margins it inhabits, but the particulars remain undocumented.
Breeding
FishBase records the reproductive mode plainly: 'Mouthbrooding by females.' Like the rest of the haplochromine flock, Haplochromis limax is a maternal (ovophile) mouthbrooder — the female takes the fertilised eggs into her mouth, where they are incubated and the fry sheltered for some days after hatching, with no paternal care. No clutch count has been published for this species; small lacustrine haplochromines of its size typically lay on the order of a few dozen comparatively large eggs per spawning (commonly cited figures for the group run to roughly 20–60 eggs), the modest fecundity being the trade-off for the protection mouthbrooding affords. Spawning is presumed to be aseasonal or weakly seasonal, as in related flock members, but the timing, egg number, incubation period and fry development for limax itself have not been documented in the literature we could verify.
In the aquarium
Haplochromis limax is essentially a specialist's fish and is only rarely kept; it has no established trade name and reaches hobbyists mainly through the small circle of enthusiasts who maintain Lake Edward–George and Victoria-region haplochromines (the Cichlid Room Companion, for instance, illustrates a Lake George male kept in Denmark). There is no published aquarium husbandry literature specific to the species, so the guidance here is the sensible default for a small, alkaline-water grazing haplochromine and should be read as such. A modest tank — on the order of 35.5–47 in in length — suits a group of one male to several females; keeping spare females spreads the male's attention and reduces harassment. Water should be hard and alkaline, mirroring the lakes: temperature around 75–82 °F and pH roughly 8.0–8.8. As an aufwuchs grazer it does best on a vegetable-forward diet — spirulina-based flake or pellet, blanched greens, and some grazing surface — rather than a protein-heavy menu, which these scrapers tolerate poorly. Tankmates should be robust but not boisterous; like most haplochromines the males can be pushy in spawning condition, and mixing with other small, similar-looking haplochromines invites hybridisation, so single-species or carefully chosen communities are best. None of this is exotic, but it is husbandry by analogy: the species' own requirements have simply not been written up.
Conservation
The IUCN Red List assesses Haplochromis limax as Least Concern, in an assessment by T.K. Twongo published on 31 January 2006, citing its distribution across the Lake Edward–George system and the absence of evidence of a major decline. That comparatively secure status sets it apart from many of its relatives: the haplochromine flocks of the African Great Lakes are among the most threatened freshwater faunas on Earth, and the neighbouring Lake Victoria flock in particular was devastated by the introduced Nile perch, eutrophication and overfishing. The Lake Edward–George system, which never received Nile perch on the same scale, has fared better, but it is not immune — siltation and nutrient loading from a growing catchment, fishing pressure, and the general degradation of inshore vegetated habitat are the kinds of pressures that bear on a shoreline grazer like this one. As a habitat that the IUCN describes as a confluence of the Albertine and Victoriine faunas, the Edward–George system carries a concentration of narrow-range endemics whose collective fate depends on keeping those inshore waters intact, even where any single species, like limax, is currently judged secure.