Taxonomy & naming
Epactionotus gracilis was described by Roberto E. Reis and Scott A. Schaefer in 1998 in American Museum Novitates (number 3254, pages 1–25), along with two sister species — E. bilineatus and E. itaimbezinho — when the authors proposed the new genus Epactionotus to accommodate a group of dwarf loricariids from coastal drainages of southern Brazil. The Catalog of Fishes (Eschmeyer, CAS; updated June 2026) recognises Epactionotus as a valid genus within Loricariidae: Hypoptopomatinae.
The genus name is derived from the Greek epaktios (at the seaside or coastal) and noton (back), a reference to the coastal river systems in which the species occur — an apt choice given that these fish inhabit the narrow Atlantic coastal drainages of southern Brazil rather than the vast interior Paraná system. The three original species share a distinctive combination of features, including the body form reflected in the epithet gracilis (slender, graceful).
Note: Roxo et al. (2019) proposed synonymising Epactionotus with Hisonotus Eigenmann & Eigenmann 1889, based on molecular phylogenetic analysis. The Catalog of Fishes records both the synonymy and the continuing validity arguments; CoF's current status entry lists the genus as valid as Epactionotus Reis & Schaefer 1998, which is the name followed here. The taxonomy of southern-Brazil Hypoptopomatinae remains an active research area.
Morphology
Adults of E. gracilis reach approximately 1.5 in standard length (SL), making it a small but not the most diminutive member of its genus. The epithet gracilis — Latin for slender — refers to the notably elongate, narrow body form that distinguishes the species from the generally more robust build of other cascudinhos. The body is dorsoventrally compressed, broad across the head and pectoral girdle and narrowing progressively toward the caudal peduncle.
The armour of overlapping bony scutes covers the body fully on the dorsal surface; the ventral surface of the head and abdomen is typically unplated or with reduced scutation, as is common in Hypoptopomatinae. The mouth is ventrally positioned with a sucking disc and fine, multicuspid teeth suited to rasping periphyton and algae from surfaces. Coloration in preserved specimens is pale to light brown, often with a faint darker lateral stripe; live colouration data are sparse given the species' absence from the aquarium trade.
No published formal description of secondary sexual dimorphism is available for E. gracilis. In related Hypoptopomatinae, males of breeding condition typically develop a cluster of hypertrophied odontodes around the snout and sometimes on the leading edge of the pectoral spine, which could serve as a diagnostic field character if observed. Morphological data beyond the original 1998 description are limited.
Habitat
Epactionotus gracilis is endemic to the Araranguá River basin in the southern portion of Santa Catarina state, Brazil (FishBase; IUCN 2022). The Araranguá is a short coastal drainage — less than 124 mi in length — that flows eastward from the highland plateaus of the Serra Geral directly to the Atlantic coast, entirely independent of the Paraná system. This isolation has produced a distinctive ichthyofauna with multiple endemic species.
The streams of the Araranguá headwaters flow over rocky substrates at moderate elevations in a subtropical climate characterised by year-round rainfall and cooler temperatures than inland tropical Brazil. Water quality in the less-disturbed headwater tributaries is high: cool, clear, well-oxygenated, with low conductivity and soft to slightly hard chemistry reflecting the granitic and basaltic geology of the Serra Geral. Temperatures in the upper catchment likely range from roughly 57 °F in winter to 75 °F in the warmest months.
The IUCN (2022) notes the species occurs in coastal drainages in the south of Santa Catarina, consistent with its restriction to this single coastal basin. The fish are assumed to occupy fast-flowing sections with rock and cobble substrate where biofilm growth is abundant — the typical microhabitat for small Hypoptopomatinae in Atlantic Forest streams.
Feeding
Like its congeners and the broader Hypoptopomatinae, E. gracilis is expected to be a periphyton grazer and biofilm rasper. Its fine multicuspid dentition is adapted to scraping the epilithic biofilm — a community of diatoms, cyanobacteria, filamentous algae, and associated fine organic matter — from rock and wood surfaces in fast-flowing water. This mode of feeding is typical across the small loricariid 'cascudinho' guild and is consistent with the species' stream microhabitat.
Published dietary data specific to E. gracilis are not available in the literature. Studies on ecologically similar Hypoptopomatinae (such as Otocinclus species and Hisonotus species in Atlantic Forest streams) routinely find that gut contents are dominated by diatoms, green algae, filamentous algae, and fine detritus, with little to no animal material. This profile would be expected in E. gracilis as well.
In any aquarium context (should the species ever be kept), a diet of natural algae growth on surfaces, spirulina-based wafers, and blanched soft vegetables would approximate its natural intake. Like Otocinclus, it is not a driftwood rasper and has no special xylophagous requirements.
Mating
No observations of courtship or mating behaviour in Epactionotus gracilis have been published. The species is essentially unknown in aquaria, and field studies of its reproductive behaviour are also absent from the literature. Inferences from the broader Hypoptopomatinae suggest that, as in Otocinclus and related genera, males would establish proximity to females during the breeding season, possibly engaging in chasing and positioning behaviour near suitable spawning microhabitats.
The limited available data on breeding seasonality in comparable small loricariids in Atlantic Forest coastal streams of southern Brazil suggest that reproduction peaks during the warmer, higher-flow months of the austral spring and summer (October–February). Cooler winter conditions at higher elevations in Santa Catarina likely suppress reproductive activity.
The role of environmental triggers such as temperature increase, rainfall, and photoperiod change in initiating spawning has not been studied in this species. Its restricted distribution and specialist habitat make field studies logistically challenging, and no captive breeding attempts appear in the literature.
Breeding
Breeding biology of Epactionotus gracilis is undescribed. Given its membership in the Hypoptopomatinae and the general spawning biology of the group, egg deposition is presumed to occur on hard substrates — on rocks, smooth wood, or in shallow crevices — with the eggs adhesive and brooded or guarded by one or both parents, more likely the male. Clutch size is unknown but expected to be modest given the parent's small body size.
Among the best-studied analogues, Otocinclus species are known to deposit eggs in clusters on plant leaves or smooth surfaces in the open, with minimal or no parental care; Hypoptopoma and related genera show somewhat different patterns. Where exactly Epactionotus falls on this spectrum has not been determined. The species' small body size (under 1.5 in SL) limits clutch size and might be associated with more intense per-egg investment.
No captive reproduction records exist. The species has no presence in the ornamental fish trade and is not held in scientific aquarium collections as far as published records indicate.
In the aquarium
Epactionotus gracilis is not found in the aquarium trade and has not been assigned an L-number or widely circulated common name. Its absence from the hobby reflects the combination of factors that characterise so many of Brazil's micro-loricariids: a small, restricted range in a non-trade collecting zone, a non-spectacular appearance, and no captive population to supply the market.
For a specialist with access to the species, its care requirements would resemble those of an Otocinclus or small Hisonotus: a cool-running planted or rocky nano-tank (15–20 US gal for a small group), strong filtration providing high oxygen and a moderate current, clean soft water with temperature in the range of 61–73 °F and pH 6.5–7.2. Given the species' origin in cold coastal streams of southern Santa Catarina, it would not thrive at tropical temperatures (above 79 °F) and would fare poorly in warm, low-oxygen conditions.
A diet of established algae growth on stones and wood, supplemented with spirulina tablets and blanched vegetables, would be appropriate. The fish are entirely harmless to plants and other small fish. Its diminutive size means it would be swamped by typical community-tank inhabitants and is best kept with small, slow-water species. Captive breeding would represent a genuine scientific and hobbyist achievement but has not yet been reported.
Conservation
The IUCN Red List assesses Epactionotus gracilis as Least Concern (2022, ICMBio, e.T167755A134709837), assessed under criteria version 3.1. However, this benign listing must be read against the species' extremely restricted range — a single, short coastal drainage in southern Santa Catarina.
The Araranguá basin faces ongoing pressures from coal mining (the region around Criciúma, SC is one of Brazil's historically important coal-mining zones), agricultural expansion, and urbanisation. Coal-mine drainage historically caused severe acidification and heavy-metal contamination of streams in the Araranguá basin, and while remediation efforts have improved conditions in some areas, the catchment remains one of the most impacted in southern Brazil in terms of industrial water pollution.
A species with the range of E. gracilis — confined to one coastal river system — is inherently sensitive to catchment-wide disturbance even if individual populations are locally stable. The 2022 IUCN assessment did not identify population decline serious enough to trigger a threatened category, but the restricted endemism and continued watershed pressure mean the species warrants monitoring. No captive-breeding programme or ex-situ conservation effort is known.