Taxonomy & naming
Haplochromis lividus was described by the British ichthyologist Peter Humphry Greenwood in 1956, in the Bulletin of the British Museum (Natural History), as part of his long campaign to make taxonomic sense of Lake Victoria's vast haplochromine species flock. The type locality is Napoleon Gulf at Bugungu, near Jinja in Uganda, at the lake's northern outlet into the Victoria Nile; the holotype is a male of about 3.5 in standard length (plus a 1 in caudal) held at the Natural History Museum, London (BMNH 1956.7.9.66-74, one of nine syntype-series specimens). The Catalog of Fishes and the CLOFFA checklist (van Oijen et al., 1991) both treat the name as valid, with no synonyms. The species belongs to the African cichlid subfamily Pseudocrenilabrinae. Its placement at genus level is, like that of hundreds of its lake-mates, genuinely unsettled. "Haplochromis" is used here in the broad, traditional sense that Greenwood himself applied; subsequent workers split the flock into many smaller genera on the basis of trophic morphology, and the rock-dwelling epilithic algae scrapers in particular were gathered into Neochromis. Haplochromis lividus is not one of those rock specialists — it is a vegetation-associated grazer — so it has remained under Haplochromis rather than being moved to Neochromis, and we keep the Haplochromis heading here. Greenwood grouped it with the other algae-grazers of the flock, and the monographic revision of Lake Victoria haplochromines by van Oijen (1990) classifies it specifically among the epiphytic algae grazers alongside Haplochromis obliquidens and Haplochromis nuchisquamulatus.
Morphology
This is a small cichlid: FishBase gives a maximum of 3.5 in standard length, and van Oijen's epiphytic-grazer group as a whole runs to about 2.5–3.5 in SL, so a large adult is roughly the length of a finger. The body is the generalized, moderately deep haplochromine shape. The diagnostic features are in the mouth: the outer teeth are closely set, movably implanted bicuspids with a flanged, often obliquely truncated major cusp, and there are generally two to five inner tooth rows. This dentition is the toolkit of a fish that combs and rasps algae from surfaces rather than one that bites chunks from rock. The name lividus, Latin for "lead-grey" or "bluish," was coined by Greenwood for the slate-grey ground colour of breeding males, which carry what he described as a vivid, almost fluorescent blue sheen. As in nearly all haplochromines, the sexes differ: males develop the bright nuptial coloration and the egg-spots (ocelli) on the anal fin that feature in spawning, while females and non-breeding fish are a plainer, more cryptic grey-brown. No detailed published meristic comparison of the two sexes for this species is readily available, so beyond the standard haplochromine pattern of male nuptial colour the extent of dimorphism is not well documented.
Habitat
Haplochromis lividus is endemic to Lake Victoria, the great shallow equatorial lake shared by Tanzania, Uganda and Kenya. FishBase records it across the northern lake (roughly 1 degrees N to 3 degrees S) and the type series came from the Napoleon Gulf near the Nile outlet. It is a fish of the shallow littoral fringe: it occurs in the inshore zone near emergent and submerged vegetation, is less frequent out in the water-lily zone and at the margins of papyrus swamps, and is commonly encountered over the rock foundations of piers. Unlike Lake Victoria's true rock cichlids, it is tied to the weedy, soft-bottomed shoreline rather than to exposed reefs. As a shallow shoreline species it lives within the uppermost few metres of the water column; Lake Victoria is itself a shallow lake (mean depth about 131 ft, maximum near 262 ft) but the inshore vegetated habitat this fish uses lies well within the surface layer. No species-specific in-situ chemistry was published with the description, so the figures here are the lake-wide envelope of the warm, hard, alkaline surface water that Lake Victoria's inshore cichlids experience: temperatures broadly in the mid-20s Celsius and a pH that runs neutral-to-alkaline, on the order of 7.2 to 9.0.
Feeding
Trophically, Haplochromis lividus is an epiphytic algae grazer — it harvests the algal film that grows on submerged plants. Greenwood's examination of stomach contents, summarized in FishBase, found that the diatoms Melosira and Rhopalodia dominated the digested material, with plant epidermis, filamentous green algae and fragmentary animal remains also present. Van Oijen's monograph describes the group's food as mainly diatoms with some insects, plus blue-green and green algae that are frequently ingested though it is unclear how much of that is actually digested; the food is scraped from plant surfaces and also taken from the bottom. The closely-set, movably implanted bicuspid teeth are well suited to this combing action. FishBase places the species at a low trophic level of about 2.4, consistent with a primary-consumer algivore. In the lake's food web it is one of the many small grazers that converted attached algae into haplochromine biomass, which in turn fed the flock's piscivores.
Mating
No courtship study specific to Haplochromis lividus has been published, so its mating behaviour is inferred from the well-documented and remarkably uniform pattern of the Lake Victoria haplochromine flock, to which Greenwood and van Oijen assign it. These are polygynous maternal mouthbrooders with no lasting pair bond. Breeding males assume their nuptial dress — here the slate-grey body and fluorescent-blue sheen that gave the species its name — and become territorial, displaying to ripe females. The male's anal-fin egg-spots are central to spawning: after the female lays a clutch and immediately takes the eggs into her mouth, she snaps at the egg-spots on the displaying male's fin, and as she does so he releases milt that fertilizes the eggs already in her buccal cavity. Mate choice in this flock is strongly visual and colour-driven, which is one reason the species are so sensitive to water clarity (see Conservation). Beyond this general scheme, the specifics of territory size, lek structure and courtship sequence for Haplochromis lividus itself are not documented.
Breeding
Haplochromis lividus is a maternal (female) mouthbrooder, as FishBase records and as is true of essentially the entire Lake Victoria haplochromine flock. After spawning, the female alone carries the fertilized eggs and then the developing larvae in her mouth, releasing fully-formed free-swimming fry only after they have absorbed the yolk; the male provides no parental care. No clutch count specific to this species appears to have been published, but the flock's small algae-grazers are low-fecundity mouthbrooders typical of the group, with broods on the order of a few dozen comparatively large eggs — far smaller clutches than the open-water egg-scatterers of other families, the trade-off being the high survival that comes from oral incubation. Detailed spawning triggers, incubation period and fry-development timing for Haplochromis lividus have not been reported in the literature; what is documented is the mode (maternal mouthbrooding) and the broad reproductive resilience FishBase infers, with a minimum population doubling time of under fifteen months.
In the aquarium
Haplochromis lividus is essentially not an aquarium fish. It is a Data Deficient Lake Victoria endemic with no established presence in the ornamental trade, no aquaculture profile, and no body of hobbyist breeding reports — unlike a handful of its colourful flock-mates (the so-called "Victorian haps") that circulate among specialist keepers. Anyone who did keep it would be extrapolating from those relatives: a small, active maternal mouthbrooder of the vegetated shallows would want a tank in the modest-to-mid range (a group in something on the order of 55 US gal or more), hard alkaline water around pH 7.5-8.5 and roughly 24-27 Celsius to match Lake Victoria, fine substrate, and a vegetable-rich, algae-based diet to suit a grazer rather than a meaty carnivore menu. Victorian haplochromines are generally kept as one male with several females to spread his attention and reduce harassment, and are prone to inter-male aggression and to hybridizing readily with congeners — so mixing related Lake Victoria species in one tank is strongly discouraged. In practice, though, this is a species to read about rather than to source; honest reporting is that it is not in the hobby.
Conservation
The IUCN Red List assesses Haplochromis lividus as Data Deficient, assessed on 31 March 2010 by Witte, de Zeeuw and Brooks. Data Deficient means the available information is insufficient to judge its extinction risk — an honest verdict for a small endemic in a flock that suffered one of the most severe vertebrate mass-declines on record. From the 1980s the introduced Nile perch (Lates niloticus), combined with eutrophication and the loss of water clarity, drove an estimated several hundred Lake Victoria haplochromine species to collapse, and many to apparent extinction. The IUCN assessment names the principal threat to Haplochromis lividus as hybridization driven by decreased water transparency: when the murky water blurs the bright nuptial colours that females use to choose conspecific mates, reproductive boundaries between closely related species break down. It is also caught incidentally in the lake fishery, though not specifically targeted. As a vegetation-associated inshore grazer it depends on the very shoreline habitats most exposed to nutrient run-off, turbidity and shoreline modification. Whether stable relict populations persist is precisely the question the Data Deficient listing leaves open.