Taxonomy & naming
Spatuloricaria evansii was originally described by George Albert Boulenger in 1892, in the Annals and Magazine of Natural History (Series 6, volume 10, number 55, article 2, page 10, Plate 1). Boulenger placed it in the genus Loricaria under the name Loricaria evansii; the original combination is listed as the only formal synonym in PlanetCatfish's Cat-eLog. The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Spatuloricaria evansii (Boulenger, 1892). Because the species was described in a genus other than Spatuloricaria, the authority is cited with parentheses.
The genus Spatuloricaria Bleeker, 1862, belongs to the subfamily Loricariinae (Armbruster, 2004; Ferraris, 2003). The genus diagnosis centres on the flat, spatula-shaped body plan — the most strongly depressed in the whiptail lineage — and a characteristic abdominal plating pattern. Spatuloricaria was revised by Isbrücker & Nijssen (1979) and further addressed in Ferraris (2003). The type locality for S. evansii is Jangada, Mato Grosso State, Brazil — a locality on the Cuiabá River, a major tributary of the Paraguay River draining the southern edge of the Pantanal.
The eponymous Evans is Dr John William Evans (1857–1930), a British geologist whose South American collections supported several Boulenger descriptions of this era.
Morphology
FishBase records a maximum length of 11 in SL (Ref. 111728), with a maximum published weight of 126 g from the same source — making S. evansii the largest well-documented member of its genus by SL and one of the more substantial loricariin whiptails. PlanetCatfish's Cat-eLog lists 8 in SL; the divergence reflects different specimen sets, and the FishBase figure from the more recent primary reference should be considered the current maximum.
The body is extremely depressed — flattened to a degree exceptional even within Loricariinae — and broadly spatula-shaped when viewed from above: widest across the pectoral girdle and head, narrowing steadily toward the tail, which carries the characteristic extended caudal filaments of large male Loricariinae. The overall impression is of a fish that has been pressed against the substrate like a leaf pressed between pages.
Dorsal ground colour is pale sandy brown to grey-brown with darker irregular mottling or a faint reticulate pattern, providing near-perfect camouflage on sand and fine gravel. The ventral surface is pale and unspotted. PlanetCatfish notes that sexing is reliable in adults: males develop heavier interopercular odontodes (cheek bristles) and thicker, slightly shorter pectoral fin spines than females, and the male's head is isosceles-triangle shaped when viewed from above (wider at the snout tip, narrower at the body junction), whereas the female's head profile is more equilateral.
Habitat
Spatuloricaria evansii occurs in the Paraguay River basin (including the type locality on the Cuiabá, a Pantanal-draining tributary in Mato Grosso, Brazil), the Beni River basin in Bolivia, and the broader Madeira drainage (PlanetCatfish; FishBase). The Paraguay system is subtropical to temperate, with marked seasonal temperature fluctuations — winter water temperatures in the lower basin can fall below 64 °F, while summer temperatures reach 82–86 °F or above. FishBase classifies the species as subtropical.
The Pantanal, through which the Cuiabá and other upper-Paraguay tributaries pass, is the world's largest tropical wetland — a vast, seasonally inundated savanna where rivers spread across enormous floodplains during the wet season and contract to deeper channels with sand and clay substrates in the dry season. Sandy riverbeds with soft substrates, moderate current, and little rooted vegetation characterise the primary microhabitats of whiptail catfishes in this system. S. evansii's extreme body compression and cryptic colouration fit the sand-flat benthic lifestyle precisely.
No detailed field water-chemistry data specific to S. evansii collection localities are currently published; the subtropical classification and Pantanal context suggest moderate hardness and near-neutral pH in the main channel, with the possibility of softer, more acidic conditions in floodplain pools during the wet season.
Feeding
Like all Loricariinae whiptails, Spatuloricaria evansii is presumed to feed primarily on aufwuchs — the biofilm of algae, diatoms, bacteria, and associated microorganisms that colonises submerged substrates. Its broad suckermouth and multicuspid dentition are typical of the scrapers in this subfamily. In the sandy, low-relief substrates of the Paraguay and Cuiabá systems, foraging likely involves rasping both the surfaces of submerged wood and the biofilm on gravel and consolidated clay-sand substrates.
In the aquarium, broadly whiptail-appropriate foods should be offered: algae wafers and spirulina-based sinking pellets are a staple; blanched vegetables including courgette (zucchini), cucumber, and sweet potato are accepted. Given the size of this species and its subtropical origin, a nutritionally complete diet with periodic protein supplementation — frozen or live bloodworm, Artemia, white mosquito larvae, and quality sinking carnivore pellets — is advisable, particularly when conditioning for breeding.
PlanetCatfish records no breeding reports, indicating S. evansii remains essentially an uncharted species in captivity. Very little specific aquarium dietary data exists; recommendations here draw from the broader Loricariinae whiptail literature and the species' inferred wild ecology.
Mating
Virtually no direct observation of mating behaviour in Spatuloricaria evansii has been published. Analogy with other Loricariinae suggests the following framework, grounded in the tribe-wide pattern documented for genera such as Loricaria, Rineloricaria, and Sturisoma.
Males are expected to develop territorial behaviour around preferred spawning sites — in this case likely flat substrate surfaces or the undersides of submerged wood and flat stones rather than vertical glass surfaces, consistent with the benthic, sand-substrate ecology of the species. Male odontodal development (cheek bristles and enlarged pectoral spine odontodes) is confirmed from PlanetCatfish morphological data, consistent with their role in intersexual signalling. The isosceles head shape in males (broader at the snout tip) relative to the more equilateral female head likely has a visual signalling function in lateral display.
For aquarium attempts, conditioning pairs with diverse live and frozen foods, cool-season temperature reduction of several degrees (mimicking subtropical winter), and the provision of suitable flat spawning substrates (slate, broad smooth stones, or flat ceramic tiles on the substrate) are the logical starting points, extrapolated from success with related genera.
Breeding
No breeding of Spatuloricaria evansii in aquaria has been documented in the published or accessible hobbyist literature, and PlanetCatfish records zero breeding reports for the species. It is therefore among the uncharted loricariin whiptails from a captive-reproduction standpoint.
Within Loricariinae, breeding strategies range from open substrate spawning with paternal or biparental care (as in Sturisoma and Loricaria) to cave or crevice spawning in some Rineloricaria. The strongly benthic habits and sandy-substrate association of Spatuloricaria suggest open substrate deposition on the riverbed is the natural mode, with the male guarding the egg mat. In closely related genera, males fan eggs, remove infertile ones, and guard the fry until dispersal.
Given the subtropical origin and the extreme seasonal temperature fluctuations of the Pantanal watershed, a marked cool-season temperature drop to 64–68 °F for several weeks, followed by gradual warming alongside protein-rich conditioning foods, represents the most physiologically sound trigger strategy for aquarium spawning attempts. The species is so rarely kept that any documented captive breeding would represent a significant contribution to the hobby literature.
In the aquarium
Spatuloricaria evansii is a rarely available, specialist fish rather than a mainstream aquarium subject. Its size (to 11 in SL) and subtropical temperature requirements set it apart from the more popular tropical whiptails. A large tank — at minimum 150 × 23.5 in footprint, ideally larger — with a fine sand or sand-gravel substrate is appropriate; a bare or gravel-only tank provides neither the foraging substrate nor the visual security a depressed benthic specialist requires.
Temperature should follow a seasonal cycle: 68–75 °F in winter months, rising to 79–82 °F in summer. This range reflects the subtropical Paraguay basin where winter cool periods are a natural feature of the environment and likely a breeding cue. The fish is not tropical in the strict sense, and continuous high temperatures may reduce long-term condition and lifespan.
Water chemistry should be moderate — pH 6.8–7.5, soft to moderately hard — with excellent filtration and regular partial water changes (25–30% weekly) to maintain low nitrate and high oxygen. Good flow is beneficial but the extreme body compression means the species can function in relatively modest current compared with rheophilic whiptails.
S. evansii is a peaceful species toward dissimilar tankmates and poses no threat to fish it cannot outcompete on the substrate. Suitable companions include peaceful mid-water species that will not harass the catfish — characins, peaceful cichlids of appropriate size, and other non-territorial bottom dwellers sharing similar temperature preferences. The species is an essentially daytime-inactive, cryptic fish and will spend most visible hours pressed motionless against the substrate.
Conservation
Spatuloricaria evansii was assessed by the IUCN Red List as Least Concern in 2020. The species occupies a substantial geographic range spanning the Paraguay, Beni, and Madeira drainages across Bolivia and Brazil, and no evidence of significant population decline was identified at assessment.
The Paraguay River basin, including the Pantanal, is under increasing pressure from agricultural intensification (particularly soybean and cattle farming) in the Mato Grosso plateau that drains into the Cuiabá River. Sedimentation from deforestation, modification of the Pantanal's natural flood pulse by upstream water management, and the direct channelisation of rivers for navigation all pose potential threats to the sandy-substrate benthic microhabitats this species occupies. The Pantanal itself experienced severe wildfires in 2020 that affected riparian zones, though aquatic habitats were less directly impacted.
At present, S. evansii is not subject to significant commercial ornamental collection; it remains an obscure species in the trade, which likely reduces collection pressure. Its conservation status appears stable, but continued monitoring of Paraguay basin freshwater ecosystems is warranted given the pace of land-use change in the region.