Taxonomy & naming
Chrysobrycon calamar was formally described in 2024 by Vanegas-Ríos, Urbano-Bonilla, and Sánchez-Garcés in the journal Zoosystematics and Evolution (volume 100, issue 2, pages 675–689; DOI 10.3897/zse.100.121499). The type locality is Caño Toño, in the Río Unilla basin near the town of Calamar, upper Río Vaupés, Guaviare Department, Colombia (approximately 2°09'50"N, 72°50'16"W, ~820 ft elevation). The holotype is deposited as MPUJ 18618; paratypes are held at ICNMHN, MLP, and MPUJ.
Eschmeyer's Catalog of Fishes (California Academy of Sciences) lists the species as valid, placed within Stevardiidae, subfamily Stevardiinae — a family that FishBase and some authorities treat as a subfamily of Characidae. The top-level family field here follows the broader Characidae treatment. The genus Chrysobrycon comprises small South American characids notable for marked sexual dimorphism, including bony fin hooks in males. Chrysobrycon calamar is currently sympatric with Aphyocharax pusillus and Charax tectifer at its type locality.
Morphology
Males of Chrysobrycon calamar reach 1.5 in standard length; females are smaller, reaching 1.5 in SL. FishBase records a maximum size of 1.5 in SL for the species. Like other members of Chrysobrycon, the species is sexually dimorphic: males bear a conspicuous dark vertical blotch on the abdomen, a well-developed humeral blotch near the shoulder, and bony hooks on the caudal and anal fins — a secondary sexual character common to several genera within Stevardiidae and used in courtship or male–male interactions.
Beyond these diagnostic features the species has the typical form of a small, moderately compressed characid. Detailed meristic and morphometric data are provided in the original description but are not reproduced here.
Habitat
Chrysobrycon calamar is known from the Río Itilla and Río Unilla basins in the upper Vaupés River drainage, at elevations of approximately 820–886 ft above sea level in Guaviare Department, Colombia. The species inhabits shallow water (less than 3 ft deep) that is clear and black-water in character, with moderate current over substrates of sand, pebbles, and rocks. This is Amazonian black water: low conductivity, slightly acidic, and rich in dissolved organic matter.
Water parameters measured at the Río Itilla type-locality site include a temperature of 78 °F, pH 6.5, dissolved oxygen 7.99 mg/L, and conductivity 14.0 µS/cm. The very low conductivity and slightly acidic pH are consistent with the geochemistry of upper Amazon tributaries draining laterite soils, where mineral salts are scarce and tannins stain the water tea-brown.
Feeding
Gut-content analysis from the original description records a diet of aquatic and terrestrial invertebrates, with identifiable remains of Diptera (flies and midges), Lepidoptera (moths or caterpillars), and Formicidae (ants). This reflects opportunistic surface and mid-column feeding on whatever invertebrates fall into or emerge from the shallow, shaded streams the species occupies.
In the aquarium, small live or frozen foods such as Daphnia, Artemia, mosquito larvae, and finely chopped bloodworm would match the natural diet closely. Good-quality micro-pellets and flake food are likely accepted as supplements, as is typical for small characids, though dedicated feeding trials for this species have not been published.
Mating
No specific mating observations for Chrysobrycon calamar have been published. Based on the biology of the genus Chrysobrycon and the broader Stevardiidae, the species is assumed to be an egg-scatterer with no parental care, spawning among fine-leaved plants or over substrate in its shallow stream habitat. The bony fin hooks present in males — a synapomorphy seen across several stevardiin genera — are associated with courtship contact behaviour, in which males use the hooks to grip or stimulate females during spawning runs.
Sexual dimorphism is pronounced: the dark abdominal blotch and humeral blotch of males are likely visual signals in mate choice or male competition, and the size difference (males larger than females at maximum reported lengths) is consistent with the pattern seen in close relatives.
Breeding
No captive-breeding records for Chrysobrycon calamar appear in the literature as of the date of this article. The species was only described in 2024 and has not, to the author's knowledge, reached the ornamental trade. Breeding behaviour can be inferred from the genus: egg-scattering open spawning over fine-leaved plants or along the substrate, adhesive or semi-adhesive eggs, and no parental care — adults should be removed after spawning to prevent egg predation.
If the habitat data (pH 6.5, 78 °F, low conductivity) are used as a guide for conditioning, replicating soft, slightly acidic, warm water in a well-oxygenated breeding setup would be the logical starting point. First foods for fry would likely need to be very small — infusoria or commercial liquid fry food — given the small adult size.
In the aquarium
Chrysobrycon calamar is not established in the ornamental trade and is unlikely to be encountered outside specialist collections or researchers working with Amazonian characids. Its small size (under 1.5 in SL), tolerance for soft acidic water, and the visual interest of the sexually dimorphic males make it a plausible candidate for species-specific nano aquaria if it were ever to become available.
Based on its documented habitat — shallow, clear black water with moderate flow, pH 6.5, temperature ~78 °F, and very low conductivity — a soft-water setup with good oxygenation, a dark substrate, and minimal mineral content would be appropriate. The species should be kept in groups to allow natural social behaviour. Tankmates, if any, should be comparably small and non-aggressive. Because the species is known only from a restricted range in Colombia, any specimens in the trade should ideally be captive-bred.
Conservation
Chrysobrycon calamar has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). The species was described only in 2024 and the data needed for a formal Red List assessment — including population size, trend, and extent of occurrence — have not yet been compiled.
The species is known from a restricted area in the upper Vaupés basin of Colombia's Guaviare Department, a region that has experienced pressure from deforestation, agricultural expansion, and resource extraction in recent decades. Given its apparently narrow range in shallow headwater streams, any future assessment should examine the extent of suitable habitat and the degree of catchment disturbance in the Río Itilla and Río Unilla drainages. As a species known from very few collection sites, precautionary caution about collection for trade is warranted.