Taxonomy & naming
Mylochromis sp. "Melanonotus Deep" has no scientific description, no describing author or year, and does not appear in Eschmeyer's Catalog of Fishes or FishBase. Its trade name pairs a resemblance to the described species Mylochromis melanonotus with a "deep" qualifier, the standard convention for a population that looks similar to a named species but is found deeper than that species' typical range. Mylochromis melanonotus takes its epithet from the Greek for "black-backed," referring to a dark stripe or saddle along the dorsal surface, a marking pattern that recurs across several genus members. This form is not claimed here to be conspecific with M. melanonotus, only to resemble it closely enough to carry the name informally; a formal comparison of specimens has not been published. No authority or publication date should be attached to it.
Morphology
As implied by the trade name, this form is expected to resemble Mylochromis melanonotus in general body shape and in carrying a dark dorsal stripe or saddle, without being formally diagnosed as the same species. No independent measurement or colour description specific to this deeper-water population has been published. Mylochromis melanonotus is documented at roughly 6.5 in TL as a genus-typical estimate, and a similar figure is reasonable here pending direct measurement. Sexual dimorphism is expected on genus-typical grounds — territorial breeding males intensifying colour and contrast relative to drab, cryptic females — but the specifics have not been separately documented for this population.
Habitat
The only recorded locality for this form is Kaporo, close to Lake Malawi's northern tip near the Tanzania-Malawi border. The "deep" qualifier in its name indicates it occupies greater depth than typical Mylochromis melanonotus populations found in the lake's mixed sand and intermediate habitat closer to shore; deeper-dwelling Malawi haplochromine populations are generally reported from sand slopes further offshore, commonly in the range of roughly 66–131 ft, though the specific depth for this Kaporo population has not been formally documented. Water at that depth remains within Lake Malawi's characteristic alkaline, well-buffered chemistry but is cooler, dimmer, and more stable than the shallows.
Feeding
This form is presumed to be a benthic invertivore in the manner typical of Mylochromis melanonotus and its close relatives, foraging over sand and mixed substrate for small invertebrates. Deeper-water populations of Malawi haplochromines in general are expected to exploit broadly similar prey to their shallower counterparts, though prey composition can shift somewhat with depth and light availability; no dedicated diet study exists for this specific population.
Mating
No study of courtship or territoriality has been published for this form. Genus-typical expectations apply: a polygynous mating system with no pair bond, males holding loosely defended territories over sand or mixed substrate and displaying to passing females. Deeper-water haplochromine populations are sometimes reported to be less densely territorial than shallow-water conspecifics, owing to lower population density and reduced competition for space at depth, but this has not been documented specifically for this form.
Breeding
Mylochromis sp. "Melanonotus Deep" is presumed to be a maternal mouthbrooder, following the universal reproductive strategy of the Lake Malawi haplochromine flock. Spawning would take place on open sand at depth, with the female taking the fertilised eggs into her mouth and brooding them through several weeks of development before releasing free-swimming fry, with no further parental care from the male. Clutch size has not been documented for this form; a modest clutch of a few dozen eggs is a reasonable estimate by analogy with similarly sized congeners.
In the aquarium
This form is not established in the aquarium hobby and no husbandry record exists for it specifically. A keeper who obtained it should follow genus-typical Mylochromis practice: a tank of at least 47–59 in, a soft sand substrate to support natural foraging, and water matched to Lake Malawi's chemistry — roughly 75–82 °F, pH 7.7 to 8.6, well-buffered. Because deeper-water Malawi cichlid populations are collected less frequently and at greater difficulty and expense, keepers who acquire this form should record and preserve the collection site rather than mixing stock from other localities.
Conservation
No IUCN Red List assessment exists for Mylochromis sp. "Melanonotus Deep", and none can until it is formally described. Its status in the wild is unassessed. Deeper-water populations are generally less accessible to inshore netting and small-scale fisheries than shallow-water species, which may afford this form somewhat less direct pressure than shallow-shelf relatives, but no population-specific data exist to characterise its status beyond "unassessed."