Taxonomy & naming
Anablepsoides derhami was described by Fels and Huber in 1985. The original description, 'Description d'une Espèce nouvelle de Rivulus du Pérou, R. derhami n.sp.', placed the fish in the genus Rivulus, which served for decades as the catch-all genus for New World rivuline killifishes. The ongoing molecular and morphological revision of that sprawling genus resulted in its dismemberment; Anablepsoides derhami now sits in the genus Anablepsoides Costa, 2011, the group that accommodates the larger-bodied, more elongate South American rivulines with a particular affinity for shallow forest-floor and pool habitats. The authority is therefore presented in parentheses, indicating that the original combination has changed. The Killifische Info reference (killifische.info) and the American Killifish Association both confirm the authority as (Fels & Huber, 1985).
FishBase also cross-references the name under its prior combination Rivulus derhami for legacy literature searches. Catalog of Fishes (Eschmeyer, Fricke & van der Laan) gives the valid name as Anablepsoides derhami (Fels & Huber, 1985), and that is the combination followed here. The killifische.info source notes a possible Orinoco Delta Venezuela connection in the collection history, though FishBase records the confirmed type locality and distribution as the Amazon basin in Peru; the IUCN assessment corroborates the Peruvian type locality and does not extend the range to Venezuela.
Morphology
FishBase records a maximum total length of 2 in for Anablepsoides derhami, placing it among the smaller members of its genus. Like most Anablepsoides, it has a slender, slightly cylindrical body deepening gently toward the midsection, with a slightly upturned mouth and dorsally placed eyes adapted for surveying the water surface and the aerial zone just above it — a feature shared across rivulines that makes them effective hunters of small invertebrates falling onto the water's surface.
Detailed colouration data for this species is sparse in the literature reviewed. South American rivulines of the Anablepsoides group typically show a brownish or olive base on the dorsal surface, with flanks that may carry a series of red or brown dots arranged in rows, and males frequently develop more intense pigmentation and extended unpaired fins during breeding condition. Sexual dichromatism — males being more boldly marked than the plainer, rounder-bellied females — is the rule across the group and is expected here, though species-specific colouration data for A. derhami is limited by the rarity of both wild-caught material and aquarium-kept specimens.
Habitat
The entire confirmed range of Anablepsoides derhami centres on the area around Tingo María in the Huánuco region of Peru, within the upper Amazon drainage. The IUCN Red List assessment (2014) notes that the species is known only from the type locality at the Universidad Nacional Agraria de la Selva — the grounds and immediate surrounds of an agricultural university — and that the area of occupancy is estimated at fewer than 10 square kilometres. No additional confirmed populations had been located at the time of assessment.
Tingo María lies in a transition zone between Andean foothills and lowland Amazonian forest, at an elevation where streams and pools can be clear to moderately stained depending on soil type and vegetation cover. FishBase records a temperature range of 72–79 °F and lists the species as a tropical freshwater benthopelagic fish — associated with the lower water column and bottom of shallow forest pools and stream margins rather than open midwater. The setting is consistent with the permanently flowing or semi-permanent pool habitats that characterise the non-annual rivuline lifestyle: water persists year-round, allowing the fish to complete a full life cycle without diapausing eggs.
Feeding
Specific dietary studies for Anablepsoides derhami are not available in the sources reviewed. By analogy with closely related Anablepsoides species and with the broader South American rivuline guild, the diet in the wild is presumed to consist primarily of small invertebrates: aquatic insects and their larvae, zooplankton, chironomid midges, small worms, and terrestrial insects landing on the water surface. The upturned mouth and dorsally placed eyes are morphological indicators of a surface- and near-surface feeding strategy.
In aquarium conditions, keeping the fish in good condition requires small live or frozen foods — brine shrimp nauplii and adults, daphnia, cyclops, and micro-worms are the staples recommended by killifish hobbyists for small rivulines of this type. The American Killifish Association rates the species as very difficult to maintain, which likely reflects a sensitivity to water quality and diet rather than unusual feeding specialisations; a varied diet of suitably sized live and frozen invertebrate prey is the practical starting point.
Mating
Anablepsoides derhami is a non-annual killifish. Its habitat in permanent or near-permanent forest streams and pools means there is no seasonal drying event that would select for diapausing eggs buried in substrate — the reproductive strategy that defines annual killifishes. Instead, A. derhami follows the plant-spawning mode characteristic of non-annual South American rivulines: a male and female pair spawn repeatedly over days or weeks, depositing small numbers of adhesive eggs among fine-leaved aquatic or surface vegetation, floating roots, or spawning mops placed at or near the water surface.
Courting males in good condition display intensified colouration and erect their unpaired fins to signal fitness to females. The pair align laterally, and a single spawning act deposits one or a small number of eggs, which adhere to the plant material or mop fibres. The process is repeated over successive days rather than in a single mass-spawning event. This protracted, low-clutch mode is the functional opposite of the annual killifish strategy, favouring survivorship of parents and modest steady egg production over boom-and-bust reproduction tied to ephemeral water.
Breeding
Eggs of Anablepsoides derhami are small, adhesive, and incubate in water — there is no diapause and no requirement to dry eggs in peat or store them in humid conditions. Incubation periods for non-annual rivulines at typical aquarium temperatures (72–79 °F) range from around two to four weeks depending on temperature; eggs should be checked regularly and any that cloud should be removed to prevent fungus spreading to viable eggs.
Hobbyists working with this species should provide fine-leaved plants such as Java moss or artificial spawning mops suspended near the surface. Eggs can be removed to a separate, shallow rearing vessel with gentle aeration; fry hatch as miniature replicas of the adults and are ready to feed immediately on the finest live foods — newly hatched brine shrimp nauplii and micro-worms are standard. Water quality in the rearing vessel is critical, as fry are sensitive to ammonia and nitrite accumulation. Small, frequent water changes with matched temperature and pH water support optimal growth. The American Killifish Association notes the species is considered very difficult to maintain, suggesting that stable, high-quality water and consistent live-food provision are not optional but essential.
In the aquarium
Anablepsoides derhami is rare in the hobby. The American Killifish Association lists it as very difficult to maintain, a rating that places it among the more demanding South American rivulines rather than in the beginner-friendly category. The challenges are partly husbandry — this is a small, somewhat delicate fish that requires pristine water quality, consistent temperatures in the 72–79 °F range, and a diet centred on live or frozen invertebrate prey — and partly availability: the species' extremely restricted range and apparent scarcity in the wild mean that captive material is seldom offered at killifish society auctions and study groups.
A small, well-planted or mop-furnished species aquarium is the appropriate setting: 5.5–10 US gal is sufficient for a pair or trio, with gentle filtration that does not create strong currents and a tight-fitting lid to prevent jumping, which is characteristic of rivulines. Tankmates should be selected with great care if used at all; other small, non-competitive killifishes or peaceful microfish of comparable size are the safest choices. Specialist killifish clubs and organisations such as the American Killifish Association are the most reliable sources for obtaining this species legitimately; trade in wild-caught specimens from such a restricted-range and Near Threatened fish should be approached with caution.
Conservation
The IUCN Red List assessed Anablepsoides derhami as Near Threatened in 2014 (assessment date 2014-04-24). The grounds for this listing are straightforward and sobering: the species is known from a single locality — the Universidad Nacional Agraria de la Selva at Tingo María — and its estimated area of occupancy is fewer than 10 square kilometres. Any development, agricultural expansion, or chemical contamination of that small habitat patch could rapidly eliminate the entire known population. Assessors recommended continued monitoring and research to determine whether additional populations exist elsewhere in the Huánuco region.
The Tingo María area sits in a zone where the Andean foothills meet Amazonian lowland forest, a landscape that has experienced significant pressure from coca cultivation, deforestation for agriculture, and associated runoff and soil disturbance. Although the university grounds may provide a degree of de facto protection, the site is not a formally protected nature reserve, and the fish's fate is directly tied to the condition of whatever watercourses and pools remain on and near the campus. A targeted survey of similar microhabitats in the broader Huallaga River drainage — of which Tingo María's waters form a part — would help determine whether the apparent single-site distribution reflects genuine rarity or gaps in collecting effort.