Taxonomy & naming
Characidium macrolepidotum was described by the German ichthyologist Wilhelm Peters in 1868. It sits in the genus Characidium, one of the largest genera in the family Crenuchidae — the South American darters — which the Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises as holding roughly 60-plus valid species, most of them small, cryptic streambed fish that are easy to overlook and historically under-collected relative to their diversity.
Crenuchidae as a whole splits loosely into the darters (Characidium and relatives) and the sailfin characins (Crenuchus, Poecilocharax), which occupy a very different niche as shy, blackwater nano-fish rather than current-loving bottom perchers. Characidium species are notoriously difficult to tell apart on external characters alone — flank blotch pattern, scale counts and fin-ray counts are typically needed for confident identification — and it is common for darters to be sold in the trade simply as "Characidium sp." without species-level confirmation.
Morphology
Characidium macrolepidotum has the classic darter body plan: an elongate, fairly cylindrical body, a pointed snout, and a subterminal or slightly upturned mouth suited to picking prey off the substrate. Like other members of the genus, its pectoral and pelvic fins are enlarged and held low and flat, acting almost like small props that let the fish brace against current on rocks or wood rather than fight the flow by swimming continuously.
Maximum size is modest — around 3 in total length, consistent with the genus generally, where most species top out in the 2.5–3 in range. Colouration in Characidium is typically muted: silvery-brown to olive flanks, often with a dark lateral stripe or a series of blotches, patterning that provides camouflage against a gravel or leaf-litter streambed rather than the bold colours associated with open-water tetras.
Habitat
Characidium macrolepidotum, like most darters in its genus, is a fish of flowing Neotropical streams and rivers rather than still floodplain water. Darters characteristically hold position on or just above the substrate in areas with noticeable current, using rocks, wood and coarse sediment as both cover and a perch from which to dart after prey.
Water across the genus's range tends toward soft and acidic to neutral, roughly pH 5.5–7.5, with the group tolerating a fairly wide temperature range (documented for the genus at around 64–81 °F), reflecting that many darter species live in cooler, well-oxygenated, moving water rather than warm, static blackwater. Specific locality and precise water-chemistry data for C. macrolepidotum itself are not well documented in accessible sources, so keepers should treat the genus-level figures as a reasonable guide rather than a species-specific certainty.
Feeding
Characidium macrolepidotum is a micro-predator, not a grazer or flake-eater by nature. In the wild it takes tiny aquatic and terrestrial insects and their larvae, picked individually off the substrate or snapped up as they drift past — a hunting style that matches its dart-and-perch behaviour rather than continuous open-water foraging.
In the aquarium this translates directly: darters frequently ignore dry flake and pellet food, especially early on, and do best offered small live or frozen foods such as bloodworm, mosquito larvae, brine shrimp, daphnia and cyclops. Feeding needs to reach the bottom, since the fish rarely rises far off the substrate to intercept food in the water column.
Mating
Documented detail on courtship in Characidium macrolepidotum specifically is sparse. Within the broader genus and family, spawning in aquarium accounts is associated with cooler water changes that mimic a seasonal shift, alongside the presence of fine-leaved plants such as Java moss, which the fish use as an egg-scattering site. There is no evidence of pair bonding, courtship display or nest-building comparable to the true piranhas or the crenuchid sailfin characins; behaviour is better described as a loose, current-triggered spawning event within a group rather than a distinct courtship ritual.
External sexual dimorphism is not well documented for this species; darters in general show little obvious difference between the sexes beyond gravid females appearing fuller-bodied when in spawning condition.
Breeding
Characidium species, including presumably C. macrolepidotum, are egg-scatterers: eggs are released over the substrate or among fine-leaved vegetation with no nest construction and no parental care, in contrast to the cave- and leaf-spawning sailfin characins (Crenuchus, Poecilocharax) elsewhere in the same family, where the male briefly tends the clutch. Hobby accounts for darter tetras describe triggering spawning with cooler water changes and providing dense, fine-leaved plants such as Java moss as an egg trap; eggs and fry are vulnerable to filter intake, so a sponge filter is recommended over an open intake during any breeding attempt.
Parental care is absent once eggs are scattered — adults do not guard or fan the clutch, and eggs and fry left with adult darters are readily eaten. Captive breeding of C. macrolepidotum specifically is not well documented; the notes above reflect what is reported for darter tetras of this genus more broadly, and a keeper should treat a home breeding attempt as exploratory rather than a well-established protocol.
In the aquarium
Characidium macrolepidotum suits a stream-style setup far better than a standard planted community tank: strong, oxygen-rich flow from a powerful filter, a substrate of sand or fine gravel, and scattered rock and driftwood to break up the current and give the fish perches to hold on. Tanks of at least 39.5 in in length are recommended for a proper group, with 30 US gal cited as a sensible minimum so several individuals can each establish a small territory without constant conflict.
Darters are social in the loose sense of tolerating conspecifics and doing better in numbers — a group of six or more is typically recommended — though they are not shoaling fish in the tetra sense and spend most of their time perched apart from one another rather than swimming together. They are also noted as capable jumpers, so a tight-fitting lid is essential. Because they are micro-predators that often refuse dry food, new keepers should be prepared to offer small live or frozen foods, at least until (if ever) a given individual accepts prepared foods. Tankmates should be other small, current-tolerant fish that will not outcompete the darters at feeding time or view them as an easy target.
Conservation
Characidium macrolepidotum has not been evaluated by the IUCN Red List, and no species-specific assessment is currently available. This is common across the genus: with roughly 60-plus described Characidium species scattered through Neotropical stream systems, many are poorly surveyed, taxonomically under-resolved, or simply too data-sparse for a formal conservation assessment, and this species falls into that category rather than being confirmed as either secure or at risk.
In the absence of a dedicated assessment, the general pressures facing small-bodied South American stream fish — damming, siltation from deforestation, and local water-quality degradation — are relevant watch items for stream-dwelling darters generally, but nothing specific to C. macrolepidotum's population trend can be stated without overreaching the available sources.