Taxonomy & naming
Spatuloricaria gymnogaster was described by Eigenmann and Vance in 1912, with the type locality recorded as Apulo in the Magdalena basin, Colombia, as formalised in Eigenmann (1912, Indiana University Studies 16:1–27). The original combination was Loricaria gymnogaster; it is currently placed in the genus Spatuloricaria, recognised in the Catalog of Fishes (Eschmeyer, CAS) as the valid name for this group of depressed, elongate loricariin whiptails. Loricaria gymnogaster Eigenmann & Vance, 1912 is retained as the basionym.
The IUCN assessment (Sanchez-Duarte 2016) and FishBase both treat S. gymnogaster as a valid species distinct from its congener S. fimbriata, which overlaps in geological age of description but differs in distribution (S. fimbriata extends into Panama and the Atrato drainage) and, notably, in adult size.
Morphology
S. gymnogaster shares the characteristic Spatuloricaria body plan: strongly depressed and elongated, with a spatulate (paddle-shaped) snout overhanging the ventrally placed suckermouth, and a fully armoured trunk covered in lateral series of bony scutes. The caudal peduncle is slender, and in mature specimens the upper caudal lobe typically carries a filamentous extension.
A size figure of 145.5 in SL appears in the FishBase database (ref 96636) but almost certainly reflects a decimal-entry error: a supporting weight record of 235.30 g from the same reference is consistent with a fish of roughly 12–14.5 in, not one approaching four metres. The corrected working estimate of approximately 14.5 in SL is used here. No published morphometric description of colour pattern or fin-ray counts specific to this species has been located in the accessible secondary literature. The specific epithet gymnogaster (bare-bellied) suggests the ventral surface lacks the scute cover or is otherwise unarmoured, a feature that may aid in distinguishing it from congeners, though field-verification of this character awaits a modern revision of the genus.
Habitat
The species is documented from the Upper and Middle Magdalena River basin in Colombia, and the IUCN assessment describes it as endemic to that drainage. The type locality, Apulo, lies in the Cundinamarca department at mid-elevation along the Magdalena valley. The IUCN (2016) characterises its habitat as small and medium-sized rivers with soft and rocky bottom substrates in permanent stream environments. No physicochemical field data (temperature, pH, conductivity, depth) for this species' collection sites are available in the published literature. FishBase records very low resilience for the population, with minimum population doubling time estimated at more than 14 years — a figure that, while model-derived, suggests it may be slow to recover from disturbance.
Feeding
FishBase assigns S. gymnogaster a trophic level of 2.0, which places it among primary consumers — algae, periphyton, and fine detritus grazers. This is consistent with the general feeding ecology of Loricariinae, in which the ventral suckermouth is adapted to scraping biofilm and organic material from hard surfaces in flowing water. No direct dietary study or gut-content analysis for this species has been published.
Mating
No mating behaviour or reproductive seasonality has been documented for S. gymnogaster. The IUCN assessment (2016) lists population trend as unknown and notes that no life history data have been published. Within the Loricariinae broadly, male territorial behaviour around spawning sites and the development of elongated caudal filaments as a secondary sexual character are common, but whether these apply to this species is unrecorded.
Breeding
Reproductive biology of S. gymnogaster is undescribed. The species is not known from the aquarium trade, and no captive breeding records exist. Loricariins typically deposit adhesive eggs on firm substrates in flowing water, sometimes with paternal care, but nothing is documented for this taxon specifically.
In the aquarium
Spatuloricaria gymnogaster has no established presence in the aquarium hobby. PlanetCatfish carries no Cat-eLog entry, no L-number has been assigned, and the IUCN notes no commercial use. No aquarium husbandry data — water conditions, feeding response, tank size requirements, or compatibility observations — are on record. Given its apparently moderate adult size (estimated around 14.5 in SL), it would be a fish for a large aquarium if it ever entered the trade, comparable in scale to other mid-to-large whiptail catfishes.
Conservation
The IUCN Red List assessed S. gymnogaster as Least Concern (LC) in an evaluation dated 10 October 2014 and published in 2016 (Sanchez-Duarte 2016, e.T49830396A61473958). The assessment notes a wide distribution within the Magdalena basin and no identified major threats, but also flags the evaluation as needing updating — now over a decade old. Population trend is listed as unknown; no data on population size, density, or trajectory exist. The IUCN identifies research needs including distribution surveys, population assessments, and threat identification. No conservation measures are currently in place for the species. FishBase records a very high fishing vulnerability score (90/100) for the species, which, combined with the population model suggesting very low natural resilience, warrants monitoring if the species is subject to any level of targeted harvest.