Taxonomy & naming
Diapoma lepiclastum was described by Luiz Roberto Malabarba, Stanley H. Weitzman, and Jorge Casciotta in 2003, in a landmark paper that established the genus Diapoma and diagnosed six new species from southern Brazil, Uruguay, and Argentina, published in Comunicações do Museu de Ciências e Tecnologia da PUCRS, Série Zoologia. The type locality is the state of Rio Grande do Sul, Brazil, within the rio Uruguay drainage. The species epithet is derived from the Greek lepís (scale) and klastós (broken into pieces), a reference to the fragile, easily shed scales that characterise members of the genus — a feature that makes fresh material essential for complete counts. Because Diapoma was newly erected in that same publication, the authority appears in parentheses: (Malabarba, Weitzman & Casciotta, 2003).
Diapoma belongs to the subfamily Stevardiinae (family Characidae), a large and phylogenetically complex clade of South American characids that includes the "crevalle tetras" and related small streamlined fishes of the Río de la Plata and Atlantic slope drainages. FishBase continues to index the species under the synonym Cyanocharax lepiclastus, but Diapoma lepiclastum is the currently accepted name per Eschmeyer's Catalog of Fishes. Phylogenetic studies, including work published on the La Plata River basin stevardiines, have confirmed the placement of D. lepiclastum within Diapoma and resolved its relationships to the other six congeners; specimen lots examined in those studies (e.g. MACN-ict 9682) span 1–1.5 in SL and were taken from the Uruguay drainage.
The genus Diapoma is distinguished within Stevardiinae by a combination of small body size, the fragile easily lost scales from which the specific epithet derives, and a suite of osteological characters detailed in the original description. Six species were included at the time of the original description; subsequent revisionary work has continued to refine species limits across this cluster of southern South American stevardiines.
Morphology
Diapoma lepiclastum is a small, streamlined characid reaching a maximum recorded standard length of 1.5 in. The body is slender and fusiform, typical of the swift-water stevardiines. The scales are notably fragile and prone to being shed or damaged during collection, a feature reflected in the species name and one that complicates morphological studies on preserved material.
As with most small stevardiines, sexual dimorphism is subtle in preserved specimens, though males of related Diapoma species may show minor differences in fin ray hooks or body proportions. No detailed colour description in life is available from the cache for this species; the genus as a whole tends toward silvery to pale yellowish tones with a lateral stripe, consistent with the cryptic coloration of small, schooling stream fishes.
Habitat
Diapoma lepiclastum is native to the rio Uruguay basin of southern South America, with the type locality in the state of Rio Grande do Sul, Brazil. The rio Uruguay system drains parts of southern Brazil, Uruguay, and northeastern Argentina before joining the Río de la Plata estuary. FishBase classifies the species as benthopelagic, freshwater, and subtropical, consistent with the cool, temperate-influenced rivers and streams of the southern cone.
The broader habitat of Diapoma species in the Uruguay drainage includes flowing streams and rivers with clear to moderately turbid water, often with riparian vegetation providing marginal cover. The subtropical latitude means water temperatures are moderate and subject to seasonal variation, with cooler winters than tropical tetra habitats farther north. Distribution data from phylogenetic studies confirm D. lepiclastum as a constituent of the Uruguay basin stevardiine fauna, alongside other members of the genus.
Feeding
No species-specific dietary data for Diapoma lepiclastum are available from the published record captured in the research cache. Based on its size, body form, and the general ecology of small stevardiine characids from subtropical South American streams, the species is likely an opportunistic invertivore, consuming small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and surface-fallen insects — in the water column and at the surface.
In an aquarium setting, small stevardiines of this type typically accept fine-particled prepared foods, microgranules, and small live or frozen invertebrates such as newly hatched brine shrimp, Daphnia, and Cyclops. Specific dietary observations for this species in captivity are lacking given its minimal presence in the hobby.
Mating
No specific mating observations for Diapoma lepiclastum have been published in the sources captured here. Based on its stevardiine phylogenetic placement and the general reproductive biology of small characids from its region, the species is expected to be an egg-scattering open spawner with no parental care, likely depositing small adhesive eggs among fine-leaved aquatic vegetation or substrates during active spawning events.
Within Stevardiinae, some genera display internal fertilisation or the insemination of eggs prior to external fertilisation, a remarkable derived trait; whether Diapoma shares this trait has not been confirmed for this species in the sources available. Seasonal spawning tied to temperature and hydrological cues is typical for subtropical South American characids, with reproductive activity likely concentrated in the warmer months.
Breeding
Diapoma lepiclastum has not been reported as bred in the aquarium hobby in the sources available, and no captive breeding accounts are documented in the research cache. As a small egg-scattering stevardiine, it would be expected to follow the pattern typical of similar characids: spawning over fine-leaved plants or spawning mops, with small adhesive eggs, no parental care, and adults that will predate eggs and fry if not separated.
For hobbyists working with the species, standard small-tetra breeding protocols — a species tank or breeding pair isolated in a well-planted or mop-equipped aquarium, slight temperature increase to trigger spawning, removal of adults post-spawning, and rearing fry on fine first foods such as infusoria and newly hatched brine shrimp — would be a reasonable starting point. Data on clutch size, incubation period, and fry development specific to D. lepiclastum are not currently available.
In the aquarium
Diapoma lepiclastum is essentially absent from the aquarium hobby and is unlikely to be encountered in the trade outside of specialist collections or direct contact with researchers working on southern South American characids. No dedicated hobbyist accounts of the species have been located.
Its small size (to 1.5 in SL), subtropical origins, and membership in the stevardiine clade suggest that basic care requirements would be similar to other small, cool-tolerant South American tetras: a well-filtered, well-oxygenated aquarium with some flow, temperatures in the low-to-mid 20s Celsius, slightly acidic to neutral pH, and a planted environment providing cover. A group of six or more individuals would be appropriate for a schooling species of this size. Any aquarist fortunate enough to obtain specimens should document behaviour and breeding carefully, as almost no captive natural-history data exist for this species.
Conservation
Diapoma lepiclastum is assessed as Least Concern (LC) on the IUCN Red List, with the assessment completed on 4 March 2021 by Flávio Lima (Universidade Estadual de Campinas). The Least Concern listing reflects that the species is not currently considered to be at elevated extinction risk, though the basis for this assessment in a species with restricted range data typical of small stream fishes reflects the information available at the time of evaluation.
The rio Uruguay basin, where D. lepiclastum occurs, is subject to ongoing pressures including hydroelectric development, agricultural runoff, riparian deforestation, and habitat modification. As a small, range-restricted stevardiine with limited distributional data, the species merits continued monitoring. Its presence across the phylogenetic literature as a study taxon may help ensure that distribution data continue to be accumulated as revisionary work in the Stevardiinae proceeds.