Taxonomy & naming
Melanocharacidium pectorale was described by the Brazilian ichthyologist Paulo Buckup in 1993, part of a wave of darter-characin species split out and formally described as researchers worked through the previously poorly resolved Characidiinae. It belongs to the family Crenuchidae — the South American darters and their relatives, including the sailfin characins Crenuchus and Poecilocharax — within the order Characiformes. The genus Melanocharacidium itself was erected by Buckup to hold a group of darters distinguished from the larger genus Characidium by details of colour pattern, fin structure and osteology.
As with much of this genus and its neighbours, M. pectorale is easy to confuse in the field and in the hobby with other small, dark-blotched Characidiinae, and species-level identification generally rests on close examination of pigmentation pattern and meristic counts rather than anything visible at a glance in an aquarium. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the governing authority for the valid name and combination; nothing in the available sources suggests a synonymy or recent revision affecting this species.
Morphology
Melanocharacidium pectorale is a small, slender, torpedo-shaped fish reaching a maximum recorded length of just 1.5 in total length, placing it firmly among the smallest characins kept in the hobby. Like other darters in the subfamily Characidiinae, it has a reduced swim bladder, which is the anatomical reason for its characteristic behaviour: rather than swimming freely through the water column, it perches on the substrate propped on its pelvic and pectoral fins and moves in short, controlled hops and darts, more reminiscent of a goby or a hillstream loach than a typical tetra-shaped characin.
Colouration in the genus generally runs to a base of muted olive, tan or grey with dark blotching or barring along the flanks — camouflage suited to a life spent motionless against rock and gravel — though the finer species-level detail of M. pectorale's pattern is not covered in the sources available here. Sexual dimorphism is not documented for this species in the material reviewed; see "Mating" below.
Habitat
The species is recorded from the Amazon and Orinoco River basins of South America, where FishBase describes it inhabiting rivers with rocky bottoms and a benthopelagic lifestyle — living at and near the substrate rather than in open water. This matches the broader ecology of Characidiinae darters generally, which favour flowing water over hard or coarse substrate where their perching, low-swim-bladder body plan is an advantage rather than a liability.
Specific water chemistry data for M. pectorale itself was not located in the available sources. Genus-level accounts for Characidium and Melanocharacidium describe a fairly wide tolerance — practical aquarium guidance for darter characins generally cites a pH range around 5.5–7.5 and temperatures of roughly 64–81 °F with moderate to strong current — but these figures should be read as genus-level context rather than a confirmed data point for this exact species.
Feeding
Darter characins are micro-predators, not grazers or flake-eaters. In the wild they pick tiny insects, insect larvae and other small invertebrates from the substrate and water column, using their perching, dart-and-strike style of movement to ambush prey rather than cruising for it. Practical hobby accounts for the genus describe them feeding readily on live and frozen foods of appropriate size — Tubifex, mosquito larvae and brine shrimp are specifically mentioned for darter characins generally — while often ignoring dry flake altogether.
For a fish this small, food size matters as much as food type: at 1.5 in total length, M. pectorale needs correspondingly tiny prey items such as baby brine shrimp, microworm, grindal worm or finely sieved frozen cyclops. Keepers should expect to feed live or frozen foods routinely rather than relying on prepared diets.
Mating
No courtship description specific to Melanocharacidium pectorale was located in the sources reviewed. Within the broader Crenuchidae, breeding behaviour is not uniform: the sailfin characins Crenuchus spilurus and Poecilocharax species are cave- or leaf-spawners in which the male takes on a period of brief guarding duty, while Characidium darters are described in hobby literature as pairing off and spawning side by side over open substrate with no ongoing parental involvement. Given that Melanocharacidium is more closely allied to Characidium than to the cave-spawning sailfin genera, the open-substrate pattern is the more plausible analogue for this species, but that inference should not be read as a confirmed account for M. pectorale itself.
No external sexual dimorphism is documented for this species in the available sources.
Breeding
There is no confirmed, species-specific breeding account for Melanocharacidium pectorale in the sources reviewed here — this is a case where the honest answer is that the data is sparse rather than absent. The closest documented analogue, Characidium darters generally, are described in hobby literature as substrate egg-scatterers: a pair spawns side by side low over the bottom, and the eggs receive no parental care, with breeders typically removing the adults after spawning to prevent the eggs being eaten.
If M. pectorale follows this pattern — plausible given its placement close to Characidium within the Characidiinae — a keeper attempting to breed it should expect a similar approach: soft, slightly acidic conditions, fine-leaved plants or a bare spawning substrate, and separation of adults from eggs. This should be treated as an informed guess based on generic darter-characin husbandry rather than a documented fact for this species.
In the aquarium
Melanocharacidium pectorale is a true nano fish and should be sized and stocked accordingly: at a maximum of 1.5 in, it is easily overwhelmed by larger, more boisterous tankmates and is best suited to a quiet, dedicated nano or species setup rather than a general community tank. Genus-level accounts for Melanocharacidium note that these darters are even more strictly bottom-bound than Characidium, and that while they are peaceful fish overall, some aggression can appear when too few individuals are kept together in a small space — suggesting a modest group is preferable to a single specimen or a pair.
A tank with a rocky or gravel substrate, moderate to strong water movement and good oxygenation suits the species' rheophilic, perching lifestyle, and cover in the form of smooth stones or driftwood gives it places to rest and retreat. Darter characins as a group are noted as capable jumpers, so a tight-fitting lid is a sensible precaution. Because it takes live and frozen micro-foods rather than flake, this is not a low-maintenance beginner fish; it suits a keeper already comfortable culturing or sourcing small live foods.
Conservation
Melanocharacidium pectorale has not been formally assessed by the IUCN Red List and is coded here as Not Evaluated. This is unremarkable for a small, range-restricted darter characin described relatively recently (1993) from South American river systems that have not been comprehensively surveyed for conservation status — many similarly obscure Crenuchidae carry the same Not Evaluated or Data Deficient designation simply because no assessment has been undertaken, not because the species is known to be secure or at risk.
No specific threats or population trend data for this species were located in the sources reviewed. As with many small, non-charismatic characins occupying a broad river basin (the Amazon and Orinoco), the general pressures facing South American freshwater fish — habitat degradation, damming and water-quality change in specific tributaries — are plausible long-term considerations, but nothing in the available sources ties a documented decline to M. pectorale specifically.