Taxonomy & naming
Leptodoras marki was formally described by José L. O. Birindelli and Luiz M. Sousa in 2010, part of a wave of revisionary work on the genus Leptodoras in the early 2000s and 2010s that resolved a long tangle of poorly distinguished Amazonian doradids. It sits in the family Doradidae, the thorny or talking catfishes, within the order Siluriformes. The Catalog of Fishes treats Leptodoras marki as a valid, currently recognised species, and the genus placement has not shifted since the original description.
As with many recently described Leptodoras, older regional catfish literature sometimes lumped similar-looking Rio Xingu doradids under other, better-known Leptodoras names before the group was carefully revised; Leptodoras marki was split out and diagnosed on its own combination of spine, fin-ray and body-proportion characters rather than inherited from an older genus. The species epithet honours a named individual (a personal dedication in the tradition typical of doradid descriptions from this period), a detail not further elaborated in the sources available here.
Morphology
Leptodoras marki is a small doradid, reaching only about 3.5 in standard length, modest even by the standards of the genus Leptodoras, whose members are generally slim-bodied, elongate thorny catfishes rather than the bulkier Megalodoras- or Pterodoras-type doradids. Like other Doradidae it carries a row of bony lateral scutes along the flank and stiff, serrated, LOCKING spines at the leading edge of the dorsal and pectoral fins — spines that can lock rigid, tangle in a net and jab an unwary hand, so this fish is best moved in a container rather than netted.
The skin beneath and around the scute row is naked rather than fully scaled, a trait shared across catfishes that makes Leptodoras marki more sensitive to copper-based and some other medications than fully scaled fish — treatments should be dosed conservatively. Detailed colour pattern and fin-ray counts are not covered in the sources available here; specific diagnostic morphology is best confirmed against the original 2010 description.
Habitat
The species is known from the Rio Fresco basin, a tributary of the Rio Xingu in the Brazilian Amazon, which serves as its type locality. Available notes on the genus and on Rio Fresco habitat point to sandy beaches and shallow water with moderate current — the kind of open, sandy-bottomed river-channel habitat typical of many small Leptodoras, rather than dense leaf-litter or blackwater pools.
The Rio Xingu system is a clearwater-to-slightly-turbid Amazonian tributary with warm, soft-to-moderate water chemistry typical of the region; exact published pH and hardness figures for Leptodoras marki specifically were not found in the cached sources, so the temperature range given here follows general Leptodoras husbandry guidance rather than a site-specific reading for this species.
Feeding
Leptodoras marki is a nocturnal benthic omnivore, foraging over the riverbed after dark for small invertebrates and organic detritus, in keeping with the feeding pattern typical of small Doradidae. In the aquarium this translates to sinking pellets, frozen foods such as bloodworm and brine shrimp, and other prepared foods offered after lights-out.
Because it is a modestly sized, sociable doradid rather than a bold competitor, food is best offered once tankmates have settled for the night so it is not out-competed at the surface or in open water. It does not need live food but will take it readily when offered.
Mating
No published account of courtship or spawning behaviour for Leptodoras marki was found in the sources available here. Reproductive biology has not been documented for most small Leptodoras species, which are rarely kept or bred in the aquarium hobby and are known mainly from museum specimens and field surveys rather than long-term aquarium observation.
Breeding
Breeding has not been recorded for Leptodoras marki in the aquarium, and the sources available here give no confirmed spawning mode for the species. Unlike the armoured callichthyid catfishes, which build floating bubble-nests, or the driftwood catfishes (Auchenipteridae), which fertilise internally, most Doradidae — including the smaller Leptodoras — are presumed egg-scatterers over open substrate with little or no parental care, based on what little is known of the family, but this has not been specifically confirmed for this species. Given its restricted known range and its absence from aquarium-breeding literature, Leptodoras marki should be considered essentially unbred in captivity; prospective keepers should not expect to reproduce it at home.
In the aquarium
Leptodoras marki stays small for a doradid, topping out around 3.5 in SL, so it does not carry the size trap that catches out keepers of larger thorny catfishes — but it is rarely available in the trade and, being known from only a small stretch of the Rio Xingu drainage, is unlikely to be a routine import. Provide a soft sandy substrate, gentle to moderate current, and open swimming space echoing the sandy-beach habitat of its type locality, with subdued lighting and some cover for daytime retreat since it is a nocturnal forager.
Two care points follow from its biology as a doradid catfish. First, its skin is naked around the scute row, so it is more sensitive than a fully scaled fish to copper and certain medications — dose conservatively. Second, it carries stiff, serrated, locking pectoral and dorsal spines that can snag in a net and jab the keeper, so it should always be moved in a container rather than netted. Keep it with calm, peaceful tankmates rather than boisterous species, in line with general guidance for small Leptodoras.
Conservation
The IUCN Red List assesses Leptodoras marki as Near Threatened, an assessment dated November 2018 under criterion B1b(iii), reflecting a restricted range tied to the Rio Fresco basin and its Rio Xingu drainage. A narrow known distribution in a single tributary system makes the species vulnerable to localised pressures — the Xingu basin has been significantly altered by hydroelectric development (notably the Belo Monte dam) and by ongoing deforestation and land-use change in the surrounding Amazon, though the sources available here do not detail a specific threat assessment beyond the IUCN status itself.
Leptodoras marki does not appear to be a significant part of the aquarium trade; its conservation relevance rests on its role as one of many narrow-range endemics whose fate is bound to the health of the Xingu river system.