Taxonomy & naming
Lebiasina marilynae was described by Netto-Ferreira in 2012, making it one of several Lebiasina species erected by that author in the early 2010s as revisionary work on the genus progressed. The valid name as governed by Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & van der Laan) is Lebiasina marilynae Netto-Ferreira, 2012.
The genus Lebiasina belongs to the family Lebiasinidae within the order Characiformes. Lebiasinidae is a strictly Neotropical family that unites two ecologically distinct groups under one roof: the slender, peaceful pencilfish genera (Nannostomus and relatives) confined largely to the Amazon and Orinoco basins, and the larger, more robustly built Lebiasina and its allies, whose ranges extend across Pacific-slope Colombia, the Orinoco drainage, and parts of the Guiana Shield. The family is defined in part by the shared absence of an adipose fin, which distinguishes lebiasinids from most other characiforms at a glance.
The specific epithet marilynae is a feminine patronym — the Latinised genitive of a personal name — honouring an individual recognised by the describing author. The name carries no geographic information about the type locality.
Morphology
Members of Lebiasina share a recognisable body plan: moderately elongate and somewhat cylindrical, with a relatively large head, a terminal mouth bearing conical teeth suited to a micropredatory lifestyle, and a robust caudal peduncle. The genus lacks an adipose fin. Scales are noticeably large relative to body length compared with pencilfish in the same family, and the lateral line is typically complete.
Coloration in the genus generally runs to olivaceous or brownish flanks with a dark midlateral stripe or a series of dark blotches extending from behind the head toward the caudal base; there is often a reddish or orange suffusion, particularly in the fins of breeding individuals. The precise colour pattern and meristic counts — lateral-line scales, fin-ray formulae, head proportions — that distinguish L. marilynae from its congeners are established in the original 2012 description and are not reproduced here without access to the primary publication. Maximum size data for this specific species are not confirmed in the sources consulted; Lebiasina species of similar build typically fall in the range of roughly 3–5.5 in total length.
Habitat
Lebiasina marilynae is a South American freshwater species; the type locality and drainage affiliation are given in the original 2012 description. Across the genus, Lebiasina species occupy a broad range of habitats — from cool, swift, well-oxygenated streams draining Pacific-slope Andean foothills in Colombia and Ecuador to warmer, slower, more tannic lowland creeks and blackwater channels in the Orinoco and Guiana Shield drainages.
Common microhabitat features across the genus include shallow water over leaf litter and coarse substrate, submerged root masses, and the margins of forest streams where overhanging riparian vegetation creates shaded, invertebrate-rich conditions. Water chemistry varies considerably by drainage: Pacific-slope populations encounter relatively hard, near-neutral to moderately acidic water, while inland Orinoco and Guiana species typically inhabit soft, acidic water with low conductivity. Specific water-parameter data for the type locality of L. marilynae are not available from the sources consulted.
Feeding
Lebiasina species are generally micropredators, a role signalled by their robust dentition and relatively large, forward-set mouth. Natural diet across the genus is inferred to consist primarily of aquatic and terrestrial invertebrates — insect larvae, small crustaceans, worms, and fallen insects taken at or near the surface — consistent with the invertebrate-rich stream-margin and leaf-litter habitats they typically occupy. Some larger individuals may take small fish fry opportunistically.
In captivity, congeners accept live and frozen invertebrate foods readily: bloodworm, Daphnia, Artemia, and similar items. High-quality carnivore pellets or sinking granules are generally taken once fish have settled. As with the genus generally, a diet weighted toward meaty live or frozen foods produces better condition and more natural colouring than a purely dried-food regime. No specific feeding observations for L. marilynae in captivity are published in the hobby literature.
Mating
No published observations of courtship behaviour in Lebiasina marilynae are available. Across the family Lebiasinidae, reproductive strategies range from open egg-scattering with no parental care (as in most pencilfish) to limited site-associative behaviour reported in some Lebiasina and Piabucina species. In the open-spawning pattern typical of the group, males actively pursue females through vegetation or over substrate, and eggs are released in small batches rather than in a single mass spawning event.
Any seasonality in reproduction is likely linked to the hydrological cycles of the native drainage — rising water levels and increased food availability in the wet season are common triggers for breeding in South American stream fishes. Whether L. marilynae shows nest-guarding, site fidelity, or other derived reproductive behaviours beyond simple egg-scattering has not been reported in the literature consulted.
Breeding
Lebiasina marilynae has not been reported bred in captivity in the accessible hobby or scientific literature. For the genus generally, reproduction follows the typical characiform pattern: small, adhesive or semi-adhesive eggs are scattered among fine-leaved vegetation or deposited over substrate, incubation is brief at tropical temperatures, and larvae become free-swimming within days. No parental care of eggs or fry has been confirmed for the genus.
Should specimens become available to dedicated breeders, conditioning on a varied diet of live and frozen invertebrate foods, a well-planted or leaf-litter-furnished aquarium, and water parameters reflecting the conditions of the type locality would be a reasonable starting approach. Any confirmed breeding records for this species would represent a notable contribution to the documentation of Lebiasinidae reproduction.
In the aquarium
Lebiasina marilynae is not established in the ornamental trade and is essentially unavailable through commercial channels. Lebiasina species appear occasionally in the specialist South American biotope trade but circulate rarely and sporadically; most aquarists will never encounter one.
Based on the genus, a keeper who obtains specimens should provide a well-filtered aquarium with ample cover — driftwood tangles, dried leaf litter, root masses, and dense planting — that replicates the shaded, structure-rich stream environments the species inhabits in the wild. A micropredatory diet of live and frozen invertebrates should be the staple. These are not community fish suited to a general tropical tank: the combination of relatively large size, strong jaws, and a predatory temperament means they are better kept with robust, similarly sized tankmates or in a species-dedicated setup. Water temperature in the 72–81 °F range, soft to moderately hard, with slightly acidic to near-neutral pH, covers the range typical of South American lebiasinid habitats, though exact parameters for this species are not confirmed.
Conservation
Lebiasina marilynae has not been confirmed to hold an IUCN Red List assessment at the time of writing. Its description in 2012 and limited profile in the ichthyological literature mean no formal evaluation has been published; the species is treated here as Not Evaluated (NE).
Many recently described Lebiasina species occupy restricted ranges in Colombian, Venezuelan, or Guianan drainages where habitat degradation through agriculture, deforestation of riparian buffers, and water-course modification poses ongoing and documented threats to freshwater biodiversity. Whether L. marilynae faces analogous pressures, or has a sufficiently broad range to be less immediately at risk, cannot be determined from available data. A formal range assessment and IUCN evaluation would meaningfully advance the conservation picture for this and other recently described members of the family Lebiasinidae.