Taxonomy & naming
Diplotaxodon sp. "Limnothrissa Blackdorsal" has no describing author, no year of publication, and no FishBase entry, since it has never been the subject of a published taxonomic description. Its trade name references the formally described Diplotaxodon limnothrissa, described by George F. Turner in 1994 and named for its resemblance to Limnothrissa miodon, a small sardine-like clupeid that shares its pelagic, planktivorous role — a comparison used here to place this form within the same general silvery, slender-bodied group. "Blackdorsal" then records the field mark separating this Tukombo population: a black dorsal fin, contrasting directly with the yellow-white blaze documented along the dorsal fin of ripe D. limnothrissa males. That contrast is the clearest documented basis for treating this as a distinct form rather than a colour variant within D. limnothrissa itself, though no genetic study has resolved the question.
Morphology
This form follows the standard Diplotaxodon body plan shared with D. limnothrissa: a slender, laterally compressed, torpedo-shaped fish built for sustained open-water swimming, with large eyes suited to the dim light of deeper or offshore water. The documented field mark is a black dorsal fin, distinguishing it from the yellow-white dorsal blaze recorded in breeding-condition D. limnothrissa males. Outside of that fin marking, sexes in the nominal species show no body-shape dimorphism, and D. limnothrissa reaches a published maximum of about 6 in SL; no species-specific measurement has been published for this Tukombo form, but a similar size is plausible given the close comparison drawn in its name.
Habitat
Diplotaxodon sp. "Limnothrissa Blackdorsal" is recorded from open water off Tukombo, on Lake Malawi's western shore. Like D. limnothrissa, it is presumed to be a pelagic, open-water fish rather than a rock- or sand-associated cichlid, occupying a wide depth range from the surface down into deep water — D. limnothrissa itself has been recorded from the surface to roughly 722 ft. Water chemistry follows Lake Malawi's standard profile — warm, alkaline, and well-buffered near the surface, with cooler, less oxygenated conditions at the depths this genus favours.
Feeding
Diplotaxodon limnothrissa is documented as a pelagic feeder on small fish and zooplankton, reflecting the broader genus pattern of open-water planktivory with some species supplementing their diet with smaller pelagic fish. "Limnothrissa Blackdorsal" is presumed to follow the same feeding ecology given its close comparison to the nominal species, though no dedicated dietary study exists for this specific form.
Mating
Reproductive behaviour in Diplotaxodon is poorly documented for the genus as a whole. Pelagic living makes courtship and spawning difficult to observe directly, since the fish do not hold conventional rock or sand territories. What is known of D. limnothrissa points to open-water breeding rather than fixed pair bonds or defended territories, consistent with the maternal mouthbrooding shared across every Malawi haplochromine, but the specific courtship sequence for "Limnothrissa Blackdorsal" has not been recorded in the literature available here.
Breeding
As with D. limnothrissa, this form is presumed to be a maternal mouthbrooder: the female takes fertilised eggs into her mouth and carries the developing brood until the fry are free-swimming. D. limnothrissa is documented as notably low-fecundity, typically carrying only one or two large, well-developed young (roughly 1 in TL) per brood, rather than the dozens typical of rock-dwelling mbuna — an unusual reproductive strategy investing heavily in few, well-developed offspring. Whether this specific figure holds for "Limnothrissa Blackdorsal" has not been confirmed, but it is presented here given the close comparison drawn in the trade name.
In the aquarium
Diplotaxodon sp. "Limnothrissa Blackdorsal" is not an established aquarium fish. Pelagic Diplotaxodon species are collected far less often than rock and sand cichlids, are more delicate in transport, and require the kind of large, open, well-oxygenated midwater space that few home aquaria can provide; the genus is essentially absent from the ordinary hobby trade. Any keeper who did encounter this form would need to approach it as a schooling open-water fish rather than a territorial cichlid — a large, uncluttered tank, strong water movement and oxygenation, and the standard alkaline, well-buffered Lake Malawi water chemistry (roughly 75–82 °F, pH 7.7–8.8) — but specific husbandry experience with this form has not been documented and none should be invented.
Conservation
Diplotaxodon sp. "Limnothrissa Blackdorsal" has no IUCN Red List assessment, since formal evaluation requires a validly published scientific name and this form has never received one; D. limnothrissa itself, by contrast, has been assessed as Least Concern. More broadly, Lake Malawi's pelagic Diplotaxodon community is exposed to pressures distinct from the inshore rock-dwellers: it overlaps with the open-water usipa (Engraulicypris sardella) and utaka fisheries, which use fine-mesh nets capable of taking cichlids as bycatch, and the genus's dependence on deep, cool, well-oxygenated water makes it potentially sensitive to the lake's documented warming and strengthening thermal stratification. No population-level data exist for this specific form to say more than that it shares those general exposures.