Taxonomy & naming
Characidium travassosi was described in 2016 by Melo, Buckup & Oyakawa in a paper reviewing the darter characins of the Iguaçu basin, published in the Brazilian journal Zoologia (SciELO). The holotype measures 1.5 in standard length, with type series specimens ranging 1–2 in SL, collected from the rio das Torres, a tributary of the rio Jordão in the Rio Iguaçu basin, Paraná, Brazil, at approximately 25°48'28"S, 51°59'01"W. The species belongs to the family Crenuchidae — the South American darters, which also includes the sailfin characins Crenuchus and Poecilocharax — within the order Characiformes.
Within the large and taxonomically dense genus Characidium, subsequent comparative work (including the 2016 description of the related species C. dumonti) places C. travassosi in the so-called "C. lauroi species group" (informally Clade C1), a cluster of highland Iguaçu-basin darters distinguished from other Characidium lineages by details of postcleithrum development and by small, faint body spotting rather than bold bars or blotches. It is diagnosed from its congeners chiefly by a reduced count of caudal-fin rays (15–18) and pectoral-fin rays (10–12) and by the absence of an adipose fin — a trait shared with only a handful of other Characidium species. As with most of this genus, there is no established common or trade name for C. travassosi in the aquarium hobby; it is essentially unknown outside ichthyological literature.
Morphology
Characidium travassosi is a small, slender, cylindrical fish typical of the genus: an elongated body built for perching and darting rather than sustained open-water swimming, a relatively small mouth, and a slim caudal peduncle. The original description gives a size range of 1–2 in standard length (roughly 1–2 in), making it one of the smaller described darters even by Characidium standards, which is itself a genus of small, often overlooked fish.
Colour pattern is understated rather than showy: the flanks carry a series of inconspicuous, small triangular to V-shaped dots rather than the continuous dark lateral stripe or bold saddle-blotches seen in some congeners, and there is no adipose fin — notable because most Characidium species retain one. Fin-ray counts are also comparatively reduced (15–18 caudal rays, 10–12 pectoral rays), one of the diagnostic features separating it from superficially similar Iguaçu-basin relatives. No sexual dimorphism has been documented for this species specifically; see "Mating" below.
Habitat
The species is known only from the rio das Torres, a small tributary stream of the rio Jordão within the upper Rio Iguaçu basin in the highlands of Paraná state, southern Brazil — part of the Serra do Mar / Mata Atlântica (Atlantic Forest) region. This is cool-water highland stream habitat rather than lowland Amazonian blackwater: Iguaçu-basin headwater creeks at this elevation run notably cooler than typical tropical Amazon systems, with clear, well-oxygenated, moving water over sand, gravel and leaf-litter substrate — exactly the kind of structured streambed where Characidium perch and dart between cover.
No detailed water-chemistry data (pH, hardness) specific to the type locality was captured in the sources available here; general Characidium care literature describes the genus broadly as tolerant of slightly acidic to neutral, moderately soft water, and that is used as a general guide below rather than as a confirmed reading for this stream. The species is currently known only from this single Iguaçu tributary system, consistent with the fine-grained local endemism typical of Serra do Mar highland darters.
Feeding
As is typical for the genus, Characidium travassosi is best understood as a micro-predator rather than an omnivorous grazer or filter-feeder. Wild Characidium forage on the streambed and among leaf litter for small aquatic insect larvae, tiny crustaceans and other invertebrate prey, picking off individual items rather than shoaling to feed in open water — no species-specific gut-content study is available for C. travassosi, but this pattern is well documented across the genus.
In the aquarium, Characidium generally do poorly on flake alone and need to be offered small live or frozen foods to thrive — frozen bloodworm and mosquito larvae, and small live foods such as cyclops, daphnia and brine shrimp are the standard genus-level recommendation. A darter that ignores flake is not being fussy; it is simply not built to recognise floating dry food as prey, and keepers should plan feeding around small, meaty, bottom-delivered items from the outset.
Mating
No courtship behaviour specific to Characidium travassosi has been documented in the sources available here. Across the genus, courtship in Characidium is not elaborate: conditioned pairs or small groups become more active around fine-leaved plants or dense cover as spawning approaches, and there is no reliably documented external sexual dimorphism in body shape or colour for most species in this genus — sex is difficult to determine outside of gravid condition in females. Nothing about pairing behaviour or sex differences specific to C. travassosi itself can be stated with confidence; this section should be treated as genus-level background rather than a description of this species.
Breeding
Characidium as a genus are egg-scatterers, not mouthbrooders, bubble-nest builders or cave spawners — a female sheds adhesive eggs, most often over or among fine-leaved plants such as Java moss, and neither parent provides care afterward. Genus-level hobby accounts describe successful home breeding in soft, slightly acidic water, with clutches in the range of roughly 150 eggs, hatching in 36–48 hours, and fry that start on infusoria before graduating to newly hatched brine shrimp.
No breeding record specific to Characidium travassosi itself was found in the sources consulted, and given how recently the species was described (2016) and how narrow its known range is, it should be assumed essentially unbred in the hobby. The account above reflects genus-level Characidium breeding biology and is offered as a plausible template, not a confirmed report for this species — anyone attempting it should expect to be working from scratch.
In the aquarium
Characidium travassosi is not established in the aquarium trade — it has no common name, no known import history, and given its narrow single-stream distribution in a Brazilian headwater, it is very unlikely to appear as a deliberately collected ornamental fish. Any care guidance here is therefore extrapolated from the genus rather than from direct experience with this species, and should be treated accordingly.
Genus-level Characidium care calls for a tank with a soft, sandy or fine-gravel bottom and some structure (driftwood, smooth stones, leaf litter) to give the fish perches, kept in a group of six or more rather than singly, since darters behave more naturally and confidently in numbers. Water movement matters more for this genus than for many characins — a moderate-to-strong current with well-oxygenated water suits their streambed habits, and given the type locality is a cool highland stream rather than lowland tropical water, this species specifically may prefer the cooler, well-oxygenated end of the typical tropical range rather than a warm blackwater setup; a cautious keeper should run it cooler than a standard community tropical tank rather than assume warm Amazonian conditions. Filter intakes should be guarded, since small darters can be drawn into open intakes. Tankmates should be small, peaceful, non-competitive bottom or midwater fish that will not out-compete a shy, perching micro-predator for food.
Conservation
The IUCN Red List assessment for Characidium travassosi lists it as Least Concern, per the cached assessment referenced here, with no known major threats reported. That said, the species is known only from a single small tributary — the rio das Torres in the upper rio Iguaçu basin — a pattern of extreme local endemism that is common among Serra do Mar highland darters and that makes a species vulnerable to any single localised disturbance (deforestation, siltation, water abstraction or damming) even where no specific threat has yet been documented.
As with many recently described, narrow-range headwater fish, formal population trend data and detailed threat assessment are limited, and the Least Concern rating should be read as reflecting the absence of a known active threat rather than a confirmed healthy or monitored population. The species is not part of the aquarium trade and there is no indication of collection pressure; the primary long-term watch items for this stream system are the general pressures facing Atlantic Forest headwater habitat in southern Brazil.