Taxonomy & naming
Lethrinops sp. "Yellow Chest" has no describing author and no listing in Eschmeyer's Catalog of Fishes; it is an informal, descriptive trade name, not a scientific one. Lethrinops was erected by Charles Tate Regan in 1922 for a genus of sand-sifting Lake Malawi haplochromines typified by Chromis lethrinus Günther, 1894, and now spans roughly two dozen formally described species plus a substantial number of undescribed local forms distinguished mainly by breeding-male colour. Senga Bay has long been a major collection point on the lake's central-west shore, close to Salima, and has produced numerous named and unnamed Lethrinops forms over decades of hobby trade; "Yellow Chest" is one of several colour-based names applied to sand-dwellers from this general area. No described species has been proposed in the accessible literature as its closest formal relative.
Morphology
The form is expected to follow the standard Lethrinops body plan: moderately elongate and laterally compressed, with a pointed head and protrusible jaws for sand-sifting. As the trade name suggests, breeding males are reported to develop a yellow wash across the breast and lower flank, likely set against blue-grey or silvery-blue tones on the back and upper body, following a colour theme repeated across several Lethrinops forms. The precise extent of the yellow and its contrast with the rest of the breeding pattern have not been formally described. Genus-typical maximum size for medium Lethrinops runs to roughly 4.5–5.5 in total length; no validated figure exists for this specific form. Females and non-breeding males are assumed silvery and largely unmarked, as is typical for the genus.
Habitat
Senga Bay offers a mix of sandy shoreline, scattered rocky points and offshore sand flats, supporting both mbuna along the rocky sections and a range of sand-dwelling haplochromines, including several Lethrinops forms, over the open bottom. "Yellow Chest" was recorded from this general area; its specific depth range is not documented, but genus-typical Lethrinops on comparable open sand occupy roughly 26–82 ft, moving in loose groups outside the breeding season. Sand-dwelling Lethrinops are known to bury themselves in the sand at night, a predator-avoidance behaviour documented across several species in the genus and likely shared by most undescribed forms occupying similar open-sand habitat. Lake Malawi's water at these depths is typically clear and well oxygenated, a legacy of the lake's great depth and permanent thermal stratification below roughly 656 ft.
Feeding
As in other Lethrinops, feeding is presumed to be sand-sifting: the fish takes mouthfuls of substrate, works it in the mouth, and expels sand through the gills while retaining chironomid larvae, ostracods and similar small invertebrates. No feeding study specific to this form has been published. The protrusible-jaw sifting mechanism at the core of Lethrinops feeding was among the trophic adaptations catalogued by Geoffrey Fryer and Trevor Iles in their influential 1972 ecomorphological survey of the Malawi haplochromine radiation, which grouped genera like Lethrinops as functionally convergent sand-sifters distinct from the biting and scraping guilds found on rock. Feeding activity is concentrated during daylight hours, when the fish forage over open bottom, typically alone or in loose, shifting groups.
Mating
Lethrinops breed on a lek system: males set up small territories on open sand and display to visiting females, who assess several males before spawning. Courtship behaviour has not been documented specifically for "Yellow Chest", but the vivid breeding colour implied by the trade name is consistent with a lek-display strategy where male colour is the primary cue used by females. As in nearly all Malawi haplochromine mouthbrooders, courting males are presumed to display the egg-spot markings on the anal fin characteristic of the group — orange or yellow ocelli that mimic eggs and prompt the female to repeatedly attempt to collect them into her mouth, a behaviour that brings her into contact with sperm and fertilises the clutch she is already carrying.
Breeding
Reproduction follows the universal Lethrinops pattern of maternal mouthbrooding: the female takes fertilised eggs into her mouth at the male's territory and carries the developing brood, unaided, for roughly three to four weeks before releasing free-swimming fry. Clutch size has not been documented for this form; genus-typical broods for medium-bodied Lethrinops number a few dozen eggs. Incubation in Malawi's warm, stable water typically runs close to three weeks; the female generally stops or greatly reduces feeding for the duration, and fry are released at a size large enough to forage and take shelter independently almost immediately. Aquarium keepers working with related Lethrinops report that a female nearing release of fry becomes noticeably reclusive, spending more time hidden and less time foraging in the open, a pattern presumed to hold for this form as well.
In the aquarium
Senga Bay forms move through the trade more often than most undescribed Lethrinops, though "Yellow Chest" specifically should still be treated as an occasional, specialist-import fish rather than a routine stock item. Standard sand-dweller care applies: a long aquarium with a deep fine-sand substrate for natural foraging behaviour, hard alkaline water matching Lake Malawi chemistry, and restrained tankmates, since Lethrinops feed more slowly and deliberately than mbuna and are easily outcompeted at feeding time. A single male kept with several females generally brings out full breeding colour with the least stress. A tank of at least 47–59 in in length suits the genus's need for open swimming and foraging space, and a sinking, protein-rich diet supplemented with some vegetable matter approximates its natural sand-sifting intake reasonably well.
Conservation
As an undescribed form, "Yellow Chest" has not been assessed by the IUCN and carries no conservation status. Senga Bay is one of the most heavily fished and most heavily collected stretches of Malawi shoreline for the aquarium trade, and sand habitats there face pressure from both artisanal fishing and coastal development, but no population data specific to this form are available. More broadly, undescribed, locality-restricted forms like this one sit outside any formal conservation framework by definition — IUCN assessment requires a validated taxonomic name — even though a population confined to a single reef or bay can in principle be as vulnerable to local disturbance as many formally listed species.