Taxonomy & naming
Odontostilbe pao was described by Lucia Bührnheim and Luiz R. Malabarba in a 2007 paper published in Neotropical Ichthyology, which simultaneously redescribed Odontostilbe pulchra (Gill, 1858) and introduced two new species from the Río Orinoco basin. The type locality is Río Pao at el Caserio El Pueblito, in the state of Cojedes, Venezuela — a lowland tributary entering the Orinoco system through the llanos.
The species is placed in the subfamily Cheirodontinae, a group of small characids united by a specialised, pointed dentition from which the subfamily takes its name (Greek cheirodon, 'hand tooth'). Odontostilbe itself is one of the more speciose cheirodontine genera and has seen ongoing taxonomic revision; several species once lumped within broad morphological concepts have been split out as more material and molecular data have accumulated. The valid name as recorded in Eschmeyer's Catalog of Fishes is Odontostilbe pao Bührnheim & Malabarba, 2007.
Morphology
Odontostilbe pao is a very small, slender fish with a maximum recorded standard length of 1 in — placing it among the smallest members of its genus. Like other Odontostilbe species it has a fusiform, laterally compressed body, large eyes relative to head size, and the semi-transparent musculature typical of small cheirodontines living in open water.
The most readily applied character for distinguishing males from females is the elongation of the second unbranched dorsal-fin ray in mature males — a feature shared with related species but useful in field and aquarium contexts. Detailed meristic and morphometric data (fin-ray counts, lateral-line scales, proportions) were established in the original description; the species was distinguished from O. pulchra and its congeners by a combination of such counts alongside pigmentation patterns on the body and fins. Published photographs and aquarium records are scarce, so the full extent of colour variation in live fish remains poorly documented.
Habitat
The known range of Odontostilbe pao is confined to the Río Pao drainage in the state of Cojedes, Venezuela, within the broader Río Orinoco basin. The Río Pao drains the central Venezuelan llanos — an immense seasonally flooded tropical savanna that ranks among the most productive freshwater systems in South America. The species is classified as benthopelagic and strictly freshwater.
The llanos environment is defined by extreme seasonality. During the wet season (May–November) vast areas of the plains flood, connecting streams, pools, and lagoons into continuous shallow wetlands; in the dry season the hydrology contracts sharply, concentrating fish in remaining water bodies. White-water conditions — slightly turbid, sediment-laden water typical of the Orinoco lowlands — prevail in the Río Pao. Temperature and pH data specific to the type locality are not available in the published literature, but the central Venezuelan llanos generally produces warm, near-neutral to mildly acidic river water.
Feeding
No dedicated feeding study has been published for Odontostilbe pao. By analogy with other cheirodontines, the diet is likely omnivorous, centred on small invertebrates — zooplankton, microcrustaceans, and insect larvae — supplemented by algae, diatoms, and organic detritus. Cheirodontines are commonly abundant mid-water schoolers in Neotropical streams and are important components of the small-fish food web, both as consumers of microinvertebrates and as prey for larger predatory fish.
In the few cases where aquarium care has been attempted for related Odontostilbe species, fish accept standard small-particle prepared foods readily and respond well to live and frozen foods such as Artemia nauplii, micro-worm, and Daphnia. Given the species' tiny size, any live or frozen food offered must be correspondingly small.
Mating
No direct observations of mating behaviour in Odontostilbe pao have been reported in the scientific or hobby literature. The sexual dimorphism noted at description — elongation of the second unbranched dorsal-fin ray in males — is consistent with the kind of fin-display ornamentation seen in other small cheirodontines where males court females through lateral displays and fin posturing.
Based on what is known of closely related species and of the subfamily broadly, spawning is presumed to follow the typical small-characid pattern: egg-scattering over fine vegetation or substrate with no parental care. Males likely establish temporary display hierarchies during the breeding period, with the elongated dorsal ray serving as a visual signal to both rivals and potential mates.
Breeding
Odontostilbe pao has not been bred in captivity in any documented account, and no husbandry protocol is established. Extrapolating from the biology of closely related cheirodontine tetras, it is reasonable to expect open-water egg-scattering over fine-leaved plants or spawning mops, with small adhesive or semi-adhesive eggs and no parental care from either sex. Adults should be removed after spawning to prevent egg predation.
The very small adult size means that fry would be extremely tiny at hatching, almost certainly requiring infusoria or paramecia as first foods before graduating to Artemia nauplii. Conditioning adults on live and frozen microfoods before any breeding attempt would be standard practice. Until captive records exist, these remain informed extrapolations rather than established facts for this species.
In the aquarium
Odontostilbe pao is not an established aquarium fish. No commercial collection from the Río Pao appears to have reached the hobby trade, and the species is absent from major hobbyist databases and forums. Its tiny size, specialised llanos habitat, and narrow known distribution place it firmly in the category of species known only from ichthyological surveys.
For any serious attempt at keeping the species, the environmental template of the Venezuelan llanos would apply: warm water (approximately 75–82 °F), gentle filtration, neutral to slightly acidic chemistry, and the company of similarly small, non-predatory tankmates. A spacious, well-planted nano tank with open water for schooling would be the logical approach. Given the absence of established trade stock, any future availability would most likely arise through specialist breeders collaborating with ichthyological collections.
Conservation
Odontostilbe pao has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). The narrow type locality — a single collection site on the Río Pao in Cojedes state — means that the true extent of the species' range, population size, and trends are unknown. Whether populations exist elsewhere in the Río Pao drainage or adjacent Orinoco tributaries has not been systematically investigated.
The Venezuelan llanos face ongoing pressures from agriculture, cattle ranching, water extraction, and oil-industry activity, all of which can alter the hydrology and water quality of lowland streams. Small, range-restricted species in this landscape are inherently vulnerable to habitat degradation, even if their conservation status has not been formally evaluated. A targeted survey to establish distribution limits and population health would be the necessary first step toward understanding whether Odontostilbe pao requires active protection.