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

Taxonomy & naming

Diplotaxodon greenwoodi was described in 1986 by Jay R. Stauffer Jr. and Kenneth R. McKaye in the Proceedings of the Biological Society of Washington (vol. 99: 29–33), under the title 'Description of a paedophagous deep-water cichlid... from Lake Malawi.' The holotype (USNM 270847) was trawled from 86 m of water about 8 km south of Mumbo Island, off Cape Maclear in the lake's south. Its validity has been upheld by every major revision since, from Eccles & Trewavas (1989) through Turner et al. (2004), Dierickx & Snoeks (2020) and Stauffer & Konings (2021).

The genus name Diplotaxodon, erected by Ethelwynn Trewavas in 1935, is built from Greek roots meaning roughly 'double-row teeth,' referring to the dentition that distinguishes the group. The species honours Peter Humphry Greenwood (1927–1995), the English ichthyologist who spent much of his career on African cichlids at the Natural History Museum in London. As a member of the family Cichlidae (subfamily Pseudocrenilabrinae), D. greenwoodi belongs to the haplochromine flock that has radiated into hundreds of species within Lake Malawi alone — but it sits in an unusual corner of that flock, among the offshore and deep-water specialists rather than the colourful rock-dwelling mbuna most hobbyists picture.

Appearance

This is the giant of its genus. FishBase lists a maximum of about 9.7 in (24.7 cm) standard length, while the IUCN assessment cites roughly 12 in (30 cm) total length — the discrepancy is mostly the difference between measuring to the tail base versus the tail tip, and both point to a fish far larger than its plankton-feeding relatives. The body is deep and strongly laterally compressed, the eye relatively small, and the mouth enormous and angled sharply upward; published figures put the gape at roughly 57–66 degrees, a structural signature of a fish that ambushes prey from below.

Colour is restrained rather than ornamental, as suits a low-light predator. The flanks and belly are silvery; breeding males darken over the dorsal surface, much of the head and the fins while keeping those silver sides, and carry multiple yellow eggspots on the anal fin. It is told from its closest look-alikes — Pallidochromis tokolosh and the more slender Diplotaxodon longimaxilla — chiefly by its deeper body and more strongly upturned mouth. Useful as those marks are, separating the deep-water Diplotaxodon by eye is genuinely hard work, which is why much of the genus's taxonomy has leaned on careful morphometrics and, more recently, genetics.

Range & habitat

Diplotaxodon greenwoodi is endemic to Lake Malawi (also called Lake Nyasa or Niassa), the deep rift lake shared by Malawi, Mozambique and Tanzania — a site where the water body, not the tank, is the point. The species was first known only from the southern lake, around Mumbo Island and Cape Maclear, but the IUCN assessment reports it as widely distributed through the south and recorded as far north as Nkhata Bay and Chizumulu Island. Reference collections describe it as effectively lake-wide but nowhere common.

It is a creature of the open shelf and reef zones at depth. FishBase gives a depth range of about 165–485 ft (50–148 m); the IUCN notes captures down to around 150 m but most specimens taken in trawls at roughly 50 m. This is the twilight world below the wind-mixed surface layer — cooler, dimmer, and in Lake Malawi ultimately bounded by a permanently anoxic deep zone that no fish can occupy. Living there shapes everything about the fish, from its large light-gathering needs to its silvered, countershaded body.

Ecology & diet

The original 1986 description framed D. greenwoodi as a paedophage — a fish that raids the mouths of brooding females for their eggs and fry. That label has softened with better data. Current treatments, including the IUCN account and recent identification monographs, regard it primarily as a piscivore: stomach analyses have turned up the remains of larger juvenile cichlids rather than mouthfuls of tiny fry. FishBase places it at a high trophic level of about 4.2, consistent with a fish that eats other fish. The upturned mouth and compressed, deep body fit a predator that hangs in open water and takes prey silhouetted above it.

That puts D. greenwoodi near the top of the offshore food web. Its genus is the dominant fish group of Lake Malawi's pelagic and deep zones — smaller Diplotaxodon such as D. limnothrissa and D. argenteus are zooplanktivores that together make up the great majority of offshore fish biomass and underpin a commercial fishery. D. greenwoodi is the large-bodied predator riding on top of that productivity, cropping the juveniles of the cichlid community at depth rather than competing for plankton.

Behavior & breeding

Direct field observation of a fish this deep is scarce, so much of what can be said is inferred from its lineage and from broader work on offshore Diplotaxodon. Like other Lake Malawi haplochromines, it is a maternal mouthbrooder: the female takes the fertilized eggs into her mouth and incubates the developing young there, and studies of offshore cichlids (Thomson et al. 1996) confirm mouthbrooding across this deep-water assemblage. The yellow eggspots on the male's anal fin are the classic haplochromine spawning cue, used in the egg-dummy courtship that this whole flock shares.

Genetics has done more than fieldwork to place the species. Phylogenomic analyses resolve D. greenwoodi as the sister of Pallidochromis tokolosh, with D. longimaxilla as the next closest relative, and a full genome of the species has been sequenced as part of work on the lake's deep-water radiation. That radiation is itself a puzzle worth flagging: several closely related, similar-looking Diplotaxodon live sympatrically at the same depths, raising real questions — explored in studies of reproductive isolation among the deep-water species — about how so many predators stay distinct in a dark, structureless habitat.

In the aquarium

For practical purposes, this fish is not an aquarium animal. Diplotaxodon greenwoodi has never been exported alive and is not maintained in captivity, and there is no body of hobbyist keeping experience behind it. The reasons are inherent to the species, not a gap in the trade: it lives at pressures and in cold, dark water that decompression and capture do not survive, it reaches a foot in length, and it is a piscivore that would treat most tankmates as food.

It is worth stating plainly because the genus name occasionally surfaces in advanced cichlid circles attached to the idea of a 'pelagic predator from Malawi,' and because the silver, deep-water Diplotaxodon are sometimes confused in conversation with the showier offshore haplochromines that do reach the hobby. If you are reading about D. greenwoodi, treat it as natural history rather than livestock. The honest hobbyist takeaway is simply that some of the most interesting cichlids in Lake Malawi are ones you will only ever meet on a research trawl or in a museum jar.

Conservation

The IUCN Red List assesses Diplotaxodon greenwoodi as Least Concern (assessed 22 June 2018; amended assessment published 2019 by Konings & Kazembe), with a population trend listed as stable. The reasoning is straightforward: it is endemic to Lake Malawi but widely distributed within it, with no major lake-wide threat specific to the species. The pressure it does face is fishing — it turns up as bycatch in deep-water demersal trawls and is taken in small numbers by the artisanal fishery on handlines and deep-set gill nets — so overfishing is flagged as a potential, not a current, threat, and the assessment recommends population monitoring.

That single 'Least Concern' line, however, sits inside a lake under real strain, and it is worth keeping the two facts side by side rather than collapsing them. The basin-scale review by Chavula et al. (2023, Journal of Great Lakes Research 49(6):102241) documents heavy overfishing across Lake Malawi — most visibly the collapse of the prized chambo (Oreochromis) stocks — together with rising sediment and nutrient loading off deforested catchments and the risk posed by invasive species. Climate adds a quieter, deeper threat: roughly 0.7 °C of warming in the shallow water column strengthens the lake's permanent stratification, and long-term records show the same warming reaching the deep water (Vollmer et al. 2005), which slows the mixing that lifts nutrients toward the surface and ultimately caps productivity. For a deep-shelf piscivore like D. greenwoodi, the exposure is indirect but real: it sits atop the offshore food web that this stratification-limited productivity feeds, and the same deep-water nets that harvest the abundant pelagic Diplotaxodon take it as bycatch. The species itself is not endangered today — but the system it depends on is the same one the fisheries and limnology literature describes as increasingly squeezed.

Diplotaxodon greenwoodi

About this species