Cichlid Atlas — the world's cichlid waters, in depth

Taxonomy & naming

Max Poll described this fish in 1984 from specimens trawled off the Congolese coast near Albertville (now Kalemie), originally placing it in the genus Haplotaxodon as Haplotaxodon melanoides. Maréchal and Poll later moved it into Benthochromis, the genus Poll had erected for these deep-living, tall-finned planktivores, and the valid name today is Benthochromis melanoides (Poll, 1984) — the parentheses signalling that original combination change. It sits in the small tribe Benthochromini within the East African cichlid subfamily Pseudocrenilabrinae. The genus name marries the Greek benthos, the depths, with chromis, an old word for a perch-like fish; the species epithet melanoides points to the dark (melano-) nape mark that helps tell it apart from its relatives.

For years the genus was a taxonomic muddle. Only two species were recognised — B. tricoti (Poll, 1948) and B. melanoides — and even those were sometimes lumped. Patrick Tawil argued in 2008 that the various deep Benthochromis were a single variable species, while in the same year Tetsumi Takahashi described a third, B. horii, in the Journal of Fish Biology, named for Michio Hori. The knot was untangled largely by hobbyist-collector Thomas Andersen, whose 2013 Cichlid News account ('Benthochromis melanoides brought to light') showed that three distinct species are caught together in the deep southern lake. Ad Konings, who had earlier been sceptical, confirmed it after personally handling fresh wild specimens, and the three-species arrangement now stands.

Appearance

This is a fairly large, laterally compressed cichlid with the long-based dorsal and anal fins typical of the genus. Reported maximum length is about 7.2 in (18.2 cm) total length, with most adults closer to 6.7 in (17 cm). Meristics from FishBase give 16–19 dorsal spines, 10–12 soft rays, and 35 vertebrae.

Colour is understated by cichlid standards. Both sexes are silvery to greyish and, crucially, lack the horizontal body stripes seen in their congeners — B. horii carries three pale longitudinal lines and B. tricoti two, while B. melanoides has none. Males show the diagnostic dark blotch on the nape, ringed by a silvery sheen and often set off by a brighter reflective mark just ahead of it, with smaller shimmering spots scattered over the upper flank and fins. Sexual dimorphism is weak; females are plainer silver-grey. Useful separating features flagged in the literature include an eye that is usually longer than the snout (eye length 112–132% of snout length), a comparatively upturned mouth, and relatively large eyes — the reverse of B. horii, which has a smaller eye and longer snout. These overlapping, subtle differences are exactly why the species hid in plain sight for so long.

Range & habitat

Benthochromis melanoides is endemic to Lake Tanganyika and, so far, has only been collected in the southern basin — from the Kalemie and Tembwe area on the Congolese shore down to Zambian waters around Nsumbu (Sumbu) Bay, Mutondwe Island and Kalambo. Its IUCN assessment notes it could plausibly occur lake-wide, but northern records remain unconfirmed; the estimated extent of occurrence is roughly 16,860 km² (about 6,510 sq mi).

This is a deep-water fish. The IUCN gives a working depth band of about 40–100 m (130–330 ft), but the historical survey data run deeper: Pearce (1985) and Coulter (1991) found it in great numbers at 160–200 m (525–660 ft), and Konings (2019) describes it becoming rare shallower than 50 m (165 ft). Hobby field accounts place the most accessible populations over rocky substrate between roughly 70 and 100 m. The water down there is cold, dimly lit and chemically the same hard, alkaline, oxygen-bearing medium that defines Tanganyika's upper layers — a pH around 8.5–9 and high mineral content — but it is a world apart from the sunlit rocky shore most hobbyists picture when they think 'rift-lake cichlid.'

Ecology & diet

Benthochromis melanoides is a planktivore. In the wild it feeds chiefly on zooplankton — copepods above all — together with other small crustaceans drifting through the deep open water, which puts it at a trophic level estimated around 3.5. Its tall, fine-finned body and forward-set mouth fit a fish that hangs in midwater and picks individual prey items rather than one that grazes substrate or hunts other fish.

In the lake's broader food web it occupies the deep, cool fringe of the pelagic and demersal community, sharing that twilight zone with its congeners B. horii and B. tricoti and with other specialist deep-water genera such as Bathybates and Trematocara. As a mid-water plankton feeder it is a link between the lake's vast zooplankton production and larger deep-living predators — a role that, importantly, ties its fortunes to the productivity of Tanganyika's pelagic zone rather than to the reefs.

Behavior & breeding

Like the rest of its genus, B. melanoides is a maternal mouthbrooder, and like the rest of its genus it is a strikingly poor producer of young. Spawning has not been observed in the wild — the depths make that nearly impossible — but aquarium accounts describe a courtship and spawning closely resembling that of B. horii, with the female taking eggs into her mouth after laying them on a flat surface. Clutches are tiny: the maximum reported in captivity is just eight eggs. Females are reported to release fry gradually, sometimes over several weeks, suggesting an unusually drawn-out brooding period.

Konings has hypothesised that, like other deep-water Tanganyikan breeders, these fish may spawn in water so dark that breeding 'colours' register only as patterns of black and white — which would explain the species' reliance on a high-contrast nape blotch and reflective flecks rather than the vivid nuptial hues of shallow cichlids. Socially the fish is mild. Wild fish associate in loose deep-water groups, and in captivity males of B. melanoides are notably less combative with one another than male B. horii, allowing several to be kept together where the related species would not tolerate it.

In the aquarium

This is a connoisseur's fish, not a beginner's. It remains genuinely rare in the hobby — partly because it was only sorted out taxonomically in the last decade, and partly because collecting it is hard and hazardous to the fish. Animals netted at 100–200 m cannot simply be hauled to the surface; like its congeners, it must be decompressed in stages over days, and rushing that step kills it through the equivalent of the bends. Survivors are correspondingly expensive.

Given a willing keeper, the practical needs mirror those of B. horii and B. tricoti. Plan on a large, calm tank — on the order of 500 litres (about 130 US gallons), at least 5 ft (150 cm) long — with subdued lighting that respects the fish's deep-water origin, a fine sand bed and a flat-topped stone as a spawning site. Hard, alkaline Tanganyikan water is essential. Diet should be small zooplankton-style foods: cyclops, daphnia, mysis, artemia and the like, live or frozen. Because it is peaceful and easily intimidated, it does best with other calm, sand-dwelling Tanganyikans such as Xenotilapia, Ectodus or Enantiopus, and poorly with boisterous mbuna-style tankmates. The lower male-male aggression of this species, relative to B. horii, makes a small group of several males and females feasible in a big enough tank. The honest caveat is breeding: even experienced keepers rarely raise fry, because the clutches are minuscule and females often release young before they can fend for themselves.

Conservation

The IUCN Red List assessed Benthochromis melanoides as Least Concern in its most recent (2025) evaluation by Y. Fermon, the same category it held in 2006. The reasoning is candid: the known range gives an extent of occurrence (~16,860 km²) that would fall within the Vulnerable threshold under range-size criteria, but no widespread major threat is documented and much of the southern shoreline it inhabits is still pristine, so the species does not currently qualify for a threatened listing. The population trend is unknown, and assessors explicitly note that if monitoring revealed a decline it could warrant uplisting. Direct pressures are modest: it is taken as incidental catch by subsistence and deep-net fisheries rather than targeted, it appears in the aquarium trade in small numbers, and as a plankton feeder it is potentially sensitive to nutrient pollution.

Those species-level pressures sit inside a lake under real strain. Lake Tanganyika has warmed and stratified more strongly over the last century, and O'Reilly and colleagues (2003, Nature, doi:10.1038/nature01833) linked reduced vertical mixing to roughly a 20% drop in primary productivity and an estimated ~30% decline in fish yields. Cohen et al. (2016, PNAS, doi:10.1073/pnas.1603237113) used sediment and fossil records to estimate that warming has already cost the lake on the order of 38% of its oxygenated benthic habitat — directly relevant to a fish that lives near the cool, deep edge of the habitable zone, where the oxygenated water runs out. Shoreline sedimentation and nutrient loading from deforestation degrade the littoral as well (Cohen et al. 1993). The pelagic fishery built on clupeids (Stolothrissa and Limnothrissa) and the Lates predators feeds four nations and is managed jointly through the Lake Tanganyika Authority, which has trialled a May–August fishing closure that the IUCN notes would also give this species breathing room to reproduce. The honest summary: B. melanoides is not itself imperilled today, but it is a deep, plankton-dependent endemic in a basin whose warming and productivity decline land hardest on exactly that guild — so its 'Least Concern' status is best read as 'safe for now, worth watching.'

Benthochromis melanoides

About this species