Taxonomy & naming
Characidium pumarinri was described by Teixeira & Melo in 2020, with the type series collected from affluents of the Río Huallaga, a major tributary of the Río Marañón in the Peruvian Amazon. It belongs to the genus Characidium within the family Crenuchidae — the South American darters — a group long associated with the characins (Characiformes) but morphologically and behaviourally distinct from open-water tetras: darters perch on the substrate on their pelvic and anal fins and move in short, quick dashes rather than swimming continuously in a shoal.
The genus Characidium is large and taxonomically active, with new species still being described from Amazonian and Andean drainages; the original description of C. pumarinri included a review of secondary sexual characters across the genus, reflecting how much of Characidium taxonomy now leans on fin pigmentation and body proportions to separate similar-looking species. As with many recently described, narrow-range Characidium, C. pumarinri has not yet been assessed by the IUCN Red List, and its status is Not Evaluated.
Morphology
Characidium pumarinri is described as notably deep-bodied for the genus, with body depth running 24-31% of standard length, and the flanks marked with 11-17 dark vertical bars over a paler ground colour — a classic darter pattern that breaks up the outline against gravel and leaf litter. Related Characidium species run small: close congeners such as C. barbosai (1.5 in SL) and C. cricarense (2 in SL) reach roughly 1.5–2 in, and C. pumarinri is inferred to fall in the same range, though no dedicated maximum-size figure has been published for the species itself.
Sexual dimorphism is pronounced and well documented in the original description: males carry darker, more extensive pigment in the anal, dorsal, pectoral and pelvic fins than females, a difference that likely intensifies with breeding condition and is one of the more reliable ways to sex a group by eye.
Habitat
The type locality is a set of small affluent streams of the Río Huallaga, itself a major tributary of the Río Marañón in the Peruvian Amazon — fast, clear headwater and tributary habitat typical of the genus, where Characidium species hold station on gravel, sand and leaf litter in areas of moving water rather than the still floodplain lakes and backwaters favoured by many other small characins.
No water-chemistry data specific to C. pumarinri has been published. Data is sparse here; keepers should default to the moderate, well-oxygenated, moving-water conditions documented for other Amazonian Characidium rather than assuming extreme blackwater parameters.
Feeding
Characidium are micro-predators of the stream bed, taking small aquatic and terrestrial insects, their larvae, and other tiny invertebrates picked off the substrate rather than filter-feeding or grazing algae. No species-specific diet study exists for C. pumarinri, but this feeding style is consistent across the genus and matches its perching, dart-and-pounce foraging behaviour.
In the aquarium, related Characidium are reported to often ignore flake food and do best on small live or frozen foods — bloodworm, brine shrimp, Daphnia and Cyclops — offered near the substrate where the fish naturally forages.
Mating
No courtship description specific to Characidium pumarinri has been published. The clearest documented sexual dimorphism in the species — darker pigment through the anal, dorsal, pectoral and pelvic fins in males — is presumed to play a role in signalling during pairing, as fin colour differences of this kind are typical breeding-condition cues in small substrate-associated characins, but this has not been directly observed or reported for this species.
Breeding
Breeding has not been documented for Characidium pumarinri specifically. The genus as a whole are egg-scatterers over the substrate: the related C. rachovii, the best-studied Characidium in the hobby, scatters roughly 150 adhesive eggs over the stream bed with no parental care, hatching in 30-40 hours in soft, acidic water. Data is sparse for C. pumarinri itself, so this pattern should be treated as an informed expectation from its congeners rather than a confirmed account for this species.
In the aquarium
There is no published aquarium care record for Characidium pumarinri specifically, so the notes below extend from the wider genus. Characidium are modest in size — likely around 1.5–2 in as adults, in line with related species — and best suited to a tank set up to mimic a small, well-oxygenated stream: fine sand or gravel, leaf litter, driftwood, and strong filtration relative to tank volume (overlarge filtration, on the order of 10-20x turnover, is commonly recommended for the genus) to keep water moving and well-oxygenated.
As micro-predators that often ignore flake, they do best offered small live or frozen foods — bloodworm, brine shrimp, Daphnia, Cyclops — delivered near the bottom. They are peaceable, retiring fish that perch rather than shoal in open water, and are easily outcompeted by faster, more boisterous tankmates at feeding time, so calm, similarly sized bottom- and mid-dwelling companions are the safer choice.
Conservation
Characidium pumarinri has not been assessed by the IUCN Red List; its status is Not Evaluated. It was described only in 2020 from a limited set of tributary streams of the Río Huallaga in the Peruvian Amazon, and no population or range data beyond the type locality has been published, so its broader distribution and any threats to it are unknown. As with many recently described, narrow-range Amazonian stream fish, an absence of assessment reflects a lack of survey data rather than any evidence the species is secure.