Taxonomy & naming
Poptella spinula was described by Garcia-Ayala, Oliveira & Benine in 2025 and is recognised as a valid species in Eschmeyer's Catalog of Fishes (CAS Ichthyology). The type locality is the Rio Tapirapé, a tributary of the Rio Tocantins basin. Because the species was named directly into Poptella — the genus in which it remains — no parenthetical authority is used.
The genus Poptella belongs to the family Characidae and comprises a handful of small, schooling characins distributed across South America east of the Andes. Poptella spinula is the most recently described member and differs from its closest relatives by a suite of characters including 9 dorsal-fin soft rays, 27–33 anal-fin soft rays, 30–31 vertebrae, a long first dorsal-fin ray, and a caudal-fin spot restricted to the upper lobe. The description, published in the Journal of Fish Biology (Garcia-Ayala et al. 2025), placed the species within a broader revision of the genus.
As a 2025 description, the species has not yet been assessed by the IUCN Red List.
Morphology
Poptella spinula is a small, slender-bodied characin reaching a maximum recorded standard length of 2 in. The body form follows the typical Poptella plan: laterally compressed, with a relatively high back behind the head and a subterminal mouth. The pigmentation pattern includes a spot on the upper lobe of the caudal fin, which distinguishes it from some congeners that show a more centrally placed or absent caudal marking.
Key meristic data from the original description and FishBase include 9 dorsal-fin soft rays, 27–33 anal-fin soft rays, and 30–31 vertebrae. The first ray of the dorsal fin is notably elongated relative to those of similar species, providing a visible fin-shape difference in the field. A short predorsal spine — the character that gives the species its name — is present anterior to the dorsal fin.
Sexual dichromatism is not described in the literature; as in many small characins in the family, males and females are likely externally similar except for slight differences in body depth when females are gravid.
Habitat
Poptella spinula is known from the upper Rio Tocantins and the middle to upper portions of the Rio Araguaia, both draining southward from the Brazilian Highlands into the Tocantins–Araguaia system before joining the Rio Pará and flowing to the Atlantic. The type locality, the Rio Tapirapé, is a clearwater tributary of the Tocantins basin.
The Tocantins–Araguaia freshwater ecoregion (FEOW ecoregion 324) is classified as a nutrient-poor clearwater system characterised by a seasonal flooding regime driven by rainfall on the Brazilian Highlands. More than 175 fish species are endemic to this ecoregion, among them 36 endemic Characidae. Water monitoring data from the Tocantins system document near-neutral conditions (pH 7.0–7.4) and warm temperatures year-round (approximately 84–86 °F), consistent with the lowland tropical rivers of central Brazil.
FishBase classifies the species as benthopelagic and freshwater, suggesting it spends time in the lower water column of rivers and streams, as is typical for small schooling characins in open-water and vegetated marginal habitats.
Feeding
No diet study specific to Poptella spinula has been published. FishBase assigns a trophic level of 3.1 ± 0.4 se, consistent with an opportunistic omnivore feeding primarily on small invertebrates with some plant material — the pattern seen in related species such as Poptella paraguayensis, which is documented to consume plant matter, fish, invertebrates, and zooplankton.
In the aquarium, small characins of this ecological guild typically accept fine-grade sinking and floating prepared foods alongside small live or frozen invertebrates — Daphnia, Artemia nauplii, micro-worms — which also serve as conditioning foods. Offering a varied diet supports condition and natural colouration better than prepared foods alone.
Mating
No published observations of courtship behaviour in Poptella spinula exist in the available literature. By analogy with other small schooling Characidae, including congener Poptella paraguayensis and the broader family, the species is expected to be an open-water egg-scatterer with no pair bond and no parental care. Males of many such species pursue gravid females and spawn in brief, energetic bursts among fine-leaved aquatic vegetation or in open water near the substrate.
In the aquarium, conditioning with live and frozen foods and a slight drop in temperature to simulate the onset of the rainy season often stimulates spawning activity in small characins from seasonal floodplain systems.
Breeding
Captive breeding of Poptella spinula has not been documented in the hobbyist or scientific literature available at the time of writing. As a member of a genus of small egg-scattering Characidae, spawning in the aquarium would be expected to follow the pattern typical of the family: adhesive or semi-adhesive eggs deposited among fine-leaved plants or over open substrate, with no parental care and a tendency for adults to consume eggs if not separated from the spawning medium.
At tropical temperatures consistent with the species' range (approximately 81–86 °F), incubation periods for small South American characins are typically 24–48 hours, with free-swimming fry appearing within a few days. Rearing fry of such small species requires infusoria or similarly fine first foods before transitioning to newly hatched brine shrimp. Because P. spinula is a very recently described species, detailed breeding reports remain to be established by hobbyists who obtain captive stock.
In the aquarium
Poptella spinula is a newly described species and not yet established in the aquarium trade. If it becomes available, its modest adult size (to 2 in SL) and the ecological profile of the genus suggest it would suit a well-filtered aquarium in the 31.5–47 in range, kept as a school of six or more individuals. Water chemistry consistent with its native clearwater rivers — warm (79–86 °F), near-neutral (pH 7.0–7.4), with relatively low conductivity — would be appropriate.
Congener Poptella paraguayensis adapts well to aquarium life and is peaceful toward similarly sized tankmates. P. spinula can be expected to behave similarly: an active, shoaling mid-water fish compatible with other small tetras, peaceful rasboras, and small corydoras catfishes. Furnishings that break up sightlines — floating plants, fine-leaved stem plants, or driftwood — help reduce stress in recently imported wild-caught individuals and complement the darkwater aesthetic of Brazilian clearwater habitats.
Conservation
Poptella spinula has not yet been assessed by the IUCN Red List; its 2025 description means the species is too recently named to appear in current assessments. FishBase notes the status as Not Evaluated. No specific threats or population-size estimates are recorded in the available literature.
The Tocantins–Araguaia ecoregion, where the species is endemic, faces pressure from hydroelectric dam development — the Tucuruí complex on the lower Tocantins is the most prominent example — along with deforestation, agricultural runoff, and water extraction in the Brazilian Highlands headwater zone. These pressures can alter the thermal and chemical regime of clearwater tributaries and fragment fish populations. With an endemic range restricted to the upper Tocantins and middle to upper Araguaia, P. spinula is geographically limited in a way that elevates its vulnerability to large-scale habitat change. Formal assessment of its status, once sufficient distributional and abundance data accumulate, will be an important conservation priority.