Taxonomy & naming
Stenolebias damascenoi was originally described by Wilson J. E. M. Costa in 1991 as Plesiolebias damascenoi, published in Ichthyological Exploration of Freshwaters (1(4):375). The type locality is recorded in the Pantanal region of Brazil, with the holotype associated with field code HVP 16-35 from that collection. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & van der Laan) treats the valid combination as Stenolebias damascenoi (Costa, 1991), with parentheses around the authority indicating that the name has been moved from its original genus.
The transfer from Plesiolebias to Stenolebias was made by Costa in 1995, in the Revue française d'Aquariologie et d'Herpétologie (21(3–4):70), when he erected the genus Stenolebias to accommodate a small group of Pantanal annual killies that he distinguished from the broader Plesiolebias assemblage on morphological grounds. Meristic data recorded for the species include dorsal-fin rays D10.1, anal-fin rays A14.0, and a lateral-line scale count of approximately 27 — a set of characters consistent with the small, slender body plan shared by its congeners.
The species epithet damascenoi honours a person named Damasceno; Costa's 1991 paper is the primary source for this patronym, which follows the convention common in South American killifish taxonomy of naming species for collecting colleagues or regional contributors to freshwater ichthyology.
Morphology
Stenolebias damascenoi is a small, slender killifish. FishBase records a maximum total length of 1.5 in, while field observations reported from collector accounts suggest many individuals in life remain closer to 1 in, making it one of the smaller annual killies of the Pantanal. The body is elongate and laterally compressed in the manner typical of the family Rivulidae, with a subterminal mouth adapted for seizing small prey at or just below the water surface.
Meristic counts — approximately ten dorsal-fin rays, fourteen anal-fin rays, and around twenty-seven lateral-line scales — place the species comfortably within the Stenolebias morphological framework. As in many rivulid killies, males carry brighter coloration than females: the sexually dichromatic patterning typical of this group includes iridescent flank patterning in males that serves in courtship and rival assessment, while females tend toward a plainer, more cryptic appearance. Detailed colour descriptions from live specimens are not well represented in the available literature, reflecting the species' modest profile in the hobby compared to flashier South American annuals.
Habitat
The species is endemic to the Pantanal region of Brazil, within the Paraguay River basin — one of the world's great seasonal wetland systems. The Pantanal undergoes an annual flood-and-drought cycle driven by regional rainfall: during the wet season the plains inundate extensively, creating temporary pools, backwaters, and flooded grasslands that fill with aquatic life; during the dry season these pools contract and many disappear entirely, leaving the substrate dry and cracked.
Stenolebias damascenoi occupies the most extreme end of this dynamic: the temporary, isolated pools that completely desiccate each year. These pools are typically shallow, often turbid or tea-coloured from decomposing organic matter, with soft mud or peat substrates where the killies spawn. Water temperatures in Pantanal pools can be warm, reflecting the tropical to subtropical climate of the region. The Paraguay River basin spans a lowland mosaic of savanna, gallery forest, and seasonally flooded plains; this annual killifish is tied specifically to the pool microhabitats within that landscape, not the permanent river channels.
Feeding
Like other small rivulid annual killies of the Pantanal, Stenolebias damascenoi is a micro-predator. The diet in the wild is composed primarily of small invertebrates available within temporary pools — microcrustaceans, insect larvae, aquatic worms, and other zooplankton-scale prey. The upturned or subterminal mouth characteristic of the rivulid body plan is suited to intercepting prey at the water surface and in the water column rather than grubbing the substrate.
In captivity the species accepts live and frozen small invertebrates readily. Nauplii of Artemia, Daphnia, small chironomid larvae, and other standard killifish foods are appropriate. Because individuals are small, prey items should be sized accordingly; overfeeding can rapidly foul the small volumes of water typically used to house annual killies, and water quality management is more effective than rationing when fish are kept at their best.
Mating
Stenolebias damascenoi is a substrate-spawning annual killifish. Courtship follows the pattern well documented across the South American annual killie group: males display to females with lateral and spread-fin posturing, leveraging their brighter coloration to signal fitness. When a female is receptive, the pair align flank-to-flank and dive together into the soft substrate of the pool bottom — typically peat, mud, or detritus — where eggs are deposited with each spawning embrace.
The eggs are buried in the substrate rather than attached to vegetation or released in open water. This substrate-diving behaviour is the diagnostic feature of annual killifish reproduction and is the mechanism by which the embryos are placed in a position to survive the dry season underground while the adults, with little remaining time in their truncated annual life cycle, continue to spawn until the pool dries. Males may court and spawn with multiple females, and in productive conditions pairs may spawn repeatedly across the wet season.
Breeding
The buried eggs of Stenolebias damascenoi undergo embryonic diapause — a state of suspended development during which metabolic activity is drastically reduced, allowing the embryo to survive desiccation of the substrate through the dry season. FishBase records an incubation period of approximately four months under laboratory conditions, consistent with the diapause biology documented across South American annual killies and supported by research on the molecular mechanisms of developmental arrest in this group.
Hatching is triggered when the pool refills with the return of seasonal rains, and fry begin feeding immediately on microorganisms in the water. Growth is rapid — it must be, since the fish's entire reproductive lifespan is compressed into a single wet season. In the hobby, keepers replicate this cycle by spawning pairs in tanks with a peat or coir substrate layer; the substrate is periodically removed and stored slightly moist in sealed bags or containers for the diapause period (typically one to four months), then re-wetted to trigger hatching. First foods for fry are microworms, vinegar eels, or freshly hatched Artemia nauplii. Because adults of this species are short-lived even by killifish standards, maintaining a colony requires consistent cycling of breeding generations.
In the aquarium
Stenolebias damascenoi is kept by specialist killifish hobbyists, primarily members of organisations such as the American Killifish Association (AKA). It is not a mainstream aquarium fish, and its culture requires familiarity with the annual-killie keeping cycle: spawning on peat, drying the substrate, storing eggs through diapause, and hatching on schedule. The reward is access to a genuinely unusual life-history strategy made visible, and a fish that completes its entire arc — from hatching to spawning to senescence — within the space of a hobby year.
Tank requirements are modest given the species' small size. A well-planted, covered tank of 5.5–10 US gal can comfortably house a trio (one male, two females); tight-fitting lids are essential, as killies of this size are capable jumpers. Water chemistry should reflect the soft, slightly acidic to neutral conditions of Pantanal seasonal pools — soft water, pH around 6.0–7.0, temperature in the range of 72–79 °F. Subdued lighting and leaf litter or peat filtration that replicates the dark, tannin-stained water of the natural habitat will keep fish in the best colour and least stressed. The species should not be combined with larger or more aggressive fish; it is best kept as a species-only setup or with comparably sized, non-competitive companions.
Data on this species' representation in hobbyist collections is limited; it has a lower profile than some of the more colourful Pantanal annuals such as Simpsonichthys or Notholebias species, but dedicated killifish societies maintain culture lines and periodically list eggs or fry for exchange.
Conservation
The IUCN Red List assessed Stenolebias damascenoi as Least Concern in its 2018 evaluation (assessed 7 November 2018). This assessment reflects the species' known occurrence within the Pantanal — a wetland system of global conservation significance that, while subject to considerable human pressure, retains large areas of seasonal habitat. The Least Concern status does not imply the species is without threats, but rather that its population is not currently considered to be declining at a rate or to a degree that would place it in a threatened category.
The Pantanal faces ongoing and intensifying pressures: agricultural expansion (soy and cattle ranching) in the surrounding cerrado and upland catchments alters hydrological regimes that drive the annual flood pulse on which the entire system depends; road construction and drainage schemes fragment and dry out marginal pool habitats; and climate variability is increasingly altering the timing and magnitude of the wet-dry cycle. For annual killies, which are tied to specific pool microhabitats that must dry predictably and refill reliably each year, disruption of the flood cycle is an existential threat. These are landscape-scale concerns that exceed any single species assessment. Stenolebias damascenoi, as a small-bodied endemic of a biologically significant seasonal wetland, merits ongoing monitoring even under a Least Concern designation, particularly if the Pantanal's hydrological integrity continues to erode.