Taxonomy & naming
Pseudocheirodon terrabae was described by William A. Bussing in 1967, with the type locality in the Río Grande de Térraba drainage of Costa Rica. Eschmeyer's Catalog of Fishes recognises the valid name as Pseudocheirodon terrabae Bussing, 1967. The genus Pseudocheirodon belongs to the family Characidae, the large and diverse neotropical characid assemblage that encompasses the bulk of what hobbyists call tetras.
The genus name combines the Greek prefix pseudo- ('false') with Cheirodon, an older genus of small South American characids, indicating a superficial resemblance. The species epithet terrabae is a Latinised form of Térraba, the name of the principal river system in the type locality region of southern Costa Rica. The species has no widely established common name in either the scientific or hobby literature.
Morphology
Pseudocheirodon terrabae is a slender, small characid reaching approximately 2 in standard length according to FishBase records. Like other members of the genus it has the typical compressed, moderately deep body plan seen across small neotropical tetras, with a relatively large eye and a subterminal mouth suited to mid-water feeding.
Detailed accounts of coloration in the literature are sparse; Costa Rican stream tetras of this size generally display a silver to greenish-silver lateral field, often with a dark lateral stripe or spot at the caudal peduncle, and transparent fins. Sexual dimorphism, if present, has not been described in accessible sources; the species is rarely encountered in the aquarium trade, so hobbyist accounts of its appearance at close range are limited.
Habitat
This species is endemic to southern Costa Rica, restricted to the Río Grande de Térraba, Río Jicote, and Río Pirrís (Parrita) river basins. These are Pacific-slope drainages that descend from the Cordillera de Talamanca through lowland forest and agricultural land before reaching the Pacific coast. FishBase records the species as benthopelagic in freshwater, with a tropical thermal range of 70–86 °F.
The rivers of the Térraba system flow through one of Central America's more biologically diverse regions, but they are also subject to significant agricultural pressure, deforestation, and altered hydrology. The restricted geographic footprint of Pseudocheirodon terrabae — limited to three adjacent but small drainages — means any degradation within that catchment directly affects the entire known population.
Feeding
No detailed dietary studies specific to Pseudocheirodon terrabae appear in the accessible literature. Based on its morphology and its membership in Characidae, the species is presumed to be a generalised omnivore feeding opportunistically on small invertebrates, insect larvae, and organic particles in the water column, as is typical for small neotropical stream tetras.
In the aquarium, if kept, it would likely accept high-quality small flake and micro-pellet foods along with frozen or live offerings such as Daphnia, Artemia nauplii, and micro-worms — the standard fare for small characids of similar size and build.
Mating
No published observations of mating behaviour in Pseudocheirodon terrabae are available in the sources consulted. As a member of Characidae, the species is expected to follow the egg-scattering open-spawning strategy typical of the family: males likely court females with fin displays and chasing, with spawning occurring over fine-leaved vegetation or substrate, after which adhesive eggs are deposited among plants or in the water column.
Costa Rican endemic stream tetras often respond to subtle seasonal cues — shifts in temperature, photoperiod, and current — that correspond with the onset of the rainy season. Whether Pseudocheirodon terrabae exhibits pronounced seasonality in reproduction is not documented.
Breeding
There are no documented captive breeding accounts for Pseudocheirodon terrabae in the accessible hobby or scientific literature. Given its close relationship to other small characids, the breeding biology is expected to conform to the family pattern: egg-scattering spawning with adhesive eggs deposited among fine-leaved vegetation, no parental care, and adults that will readily consume their own eggs if not separated.
A successful breeding attempt would likely require soft to moderately soft, slightly acidic water reflecting the species' origin in Pacific-slope Costa Rican rivers, temperatures in the lower part of its recorded range (around 72–77 °F to simulate cooler upland tributaries), and a well-planted or moss-furnished tank. The rarity of the fish in the trade means captive-breeding experience with it is essentially absent from the public record.
In the aquarium
Pseudocheirodon terrabae is essentially absent from the mainstream aquarium hobby. It is not commercially bred or traded in meaningful quantities, and the few specimens that have appeared in collections have typically been wild-caught research or incidental imports. Its Vulnerable status on the IUCN Red List and the restrictions on collecting from Costa Rican protected watersheds mean commercial availability is unlikely to change substantially.
For the specialist interested in Central American stream fishes, a setup mimicking the Térraba drainage — moderate current, well-oxygenated water in the 72–79 °F range, neutral to slightly acidic pH, fine-leaved plants and leaf litter — would be the appropriate framework. The species' small size (around 2 in) and presumed peaceful temperament suggest it could be maintained in a community of comparably sized, non-aggressive Central American tetras and small catfish, though any such attempt should use legally and ethically sourced specimens.
Conservation
Pseudocheirodon terrabae is assessed as Vulnerable (VU) on the IUCN Red List under criteria B1ab(iii)+2ab(iii), with the assessment dated 14 May 2019. The listing reflects the species' restricted range — confined to the Río Grande de Térraba, Río Jicote, and Río Pirrís basins in southern Costa Rica — and ongoing habitat degradation within those drainages. The criteria applied indicate that both the extent of occurrence and the area of occupancy fall below Vulnerable thresholds, and that continuing decline in the quality of suitable habitat is the primary driver.
Habitat loss in these Pacific-slope drainages is driven by agricultural expansion, particularly pineapple and oil palm cultivation, deforestation in the upper catchments, and water extraction and channelisation associated with farming. Costa Rica's conservation framework includes protected areas in parts of the Talamanca highlands, but lowland and mid-elevation reaches of the Térraba system face ongoing pressure. The species' narrow endemism leaves it without refuge populations elsewhere; any significant decline in the Térraba drainage directly threatens the entirety of its known range.