Taxonomy & naming
Gephyrocharax martae was described by George Dahl in 1943. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & van der Laan) treats Gephyrocharax martae Dahl, 1943 as the valid name; since the species was described directly in Gephyrocharax, the authority is unparenthesised.
The genus Gephyrocharax belongs to the tribe Stevardiin within the family Characidae — a diverse Neotropical group sometimes treated as the subfamily Stevardiinae. Phylogenetic work by Vanegas-Rios (2018), published in the Zoological Journal of the Linnean Society, resolved G. martae as sister to a clade that includes G. chocoensis, G. major, G. atracaudatus, and G. intermedius, placing it within a well-supported western South American assemblage. An earlier comparative study by Vanegas-Rios and Phillip (2013) examined all recognised Gephyrocharax species — including a Colombian specimen of G. martae (ZMUL 3703, 1.5 in SL) — and provided diagnostic morphological data for the genus.
The type locality has been reported in different sources as either the upper Magdalena River basin or the San Jorge River basin of Colombia; both drainages are in the same general north-Andean region.
Morphology
Gephyrocharax martae is a small, laterally compressed characid with a maximum recorded standard length of 1.5 in. Like other members of its genus it carries the characteristic abdominal keel — a row of modified, gland-bearing scales along the ventral midline — that unites Gephyrocharax as a natural group and distinguishes it from superficially similar small tetras.
Colouration is typical for the genus: an overall silvery body with a thin, dark lateral stripe and a hyaline to faintly yellowish fin complement. The caudal fin may show a dark basal blotch or stripe entering the lower lobe, a character useful in separating some Gephyrocharax species. Detailed meristic counts (scale rows, fin-ray formulae, branched dorsal rays) provided in the 2013 comparative study allow separation of G. martae from congeners, though in preserved material the species is unremarkable to the non-specialist eye.
Habitat
Gephyrocharax martae is known from the upper Magdalena River basin in Colombia, a major Andean drainage running north between the Eastern and Central Cordilleras before emptying into the Caribbean. FishBase records the species as a freshwater benthopelagic fish inhabiting tropical latitudes, consistent with the warm Andean foothill and lowland streams of the Magdalena system.
No detailed microhabitat data have been published for this species. By analogy with better-studied Gephyrocharax congeners, it likely occupies clear to moderately turbid forest streams and river margins, associating with submerged vegetation or leaf litter near the bank. The Magdalena basin supports extraordinary fish diversity but has been substantially altered by deforestation, agriculture, and sedimentation in many reaches.
Feeding
No published dietary data specific to Gephyrocharax martae exist in the available literature. Gephyrocharax species generally are opportunistic micropredators and omnivores, taking small invertebrates — aquatic insect larvae, microcrustaceans, and terrestrial insects that fall to the water surface — as well as algal and detrital material. The abdominal gland keel is associated with secretions used in courtship rather than feeding, so it does not imply any specialised foraging strategy.
In captivity, small Stevardiin characids of comparable size accept fine-grade quality flake, micro-pellets, and live or frozen Daphnia, baby brine shrimp, and Cyclops without difficulty. Offering a varied diet sustains condition and promotes natural behaviour.
Mating
No specific mating observations have been published for Gephyrocharax martae. Members of the Stevardiin group, including Gephyrocharax, are generally egg-scatterers with internal fertilisation preceding external oviposition — a derived trait of the tribe in which females receive sperm from males and then deposit fertilised eggs, often among fine-leaved aquatic plants, with no parental care.
The abdominal glandular keel of Gephyrocharax is believed to function in close-range courtship signalling, with the male positioning beneath the female and exposing the keel region. The specifics of courtship behaviour in G. martae are undescribed in the literature.
Breeding
No captive breeding records for Gephyrocharax martae appear in the published or hobbyist literature reviewed. Based on the tribe's general biology, spawning would be expected to involve adhesive or semi-adhesive eggs deposited among fine-leaved vegetation, with no parental investment; the eggs would hatch into small, initially yolk-sac-dependent larvae requiring very fine first foods once free-swimming.
The species is essentially absent from the ornamental trade, so breeding protocols have not been developed or documented.
In the aquarium
Gephyrocharax martae is not an established aquarium fish. It does not appear in commercial ornamental-fish catalogues and is unknown in the hobby outside occasional scientific specimens. Any aquarist who obtained wild-caught material would be keeping a fish for which no husbandry literature exists.
By extension from comparable small Stevardiin species, it would likely do best in a well-planted aquarium with soft to moderate water, tropical temperatures in the mid-to-upper 20s Celsius, and fine-grade live or frozen foods. A species tank or a community of similarly sized, peaceful Neotropical fishes would be appropriate. Given the IUCN Data Deficient status and the lack of wild-population data, collection for the ornamental trade without proper assessment would be inadvisable.
Conservation
Gephyrocharax martae is assessed as Data Deficient (DD) on the IUCN Red List, in an evaluation carried out on 10 October 2014. The Data Deficient designation does not imply that the species is necessarily threatened, but that insufficient information exists to make a reliable determination of its risk category — the species has been collected so rarely that population size, range extent, and trend are all essentially unknown.
The Magdalena River basin, the species' home, is one of the most heavily modified river systems in South America: deforestation, agricultural runoff, artisanal gold mining, and urban effluents have degraded water quality across much of the drainage, and overfishing of the food-fish fauna has cascading effects on smaller species. Without targeted surveys, it is impossible to say whether G. martae remains locally common in suitable microhabitats or has declined. Revisiting its status with modern field sampling is the most immediate conservation need.