Taxonomy & naming
The species was described by the Belgian-British ichthyologist George Albert Boulenger in 1890 as Haplochilus hartii, with the type locality recorded as the Río Copei on Isla Margarita, Venezuela. The authority is presented in parentheses because the name has since been moved from Haplochilus to Rivulus. The Catalog of Fishes (Eschmeyer, Fricke & van der Laan) records the valid combination under Anablepsoides hartii, using the corrected epithet spelling harti; the USGS nonindigenous species database records the spelling variant Anablepsoides hartii in parallel with older literature.
A current taxonomic reassignment places the species in Anablepsoides — a genus resurrected to accommodate a clade of South American and Caribbean rivulines formerly lumped in Rivulus sensu lato — and the combination Anablepsoides hartii appears in recent molecular-based classifications. Because the Catalog of Fishes remains the formal nomenclatural authority for this site, Anablepsoides hartii is retained here, with Anablepsoides hartii noted as the alternative currently in use. The specific epithet honours an unrecorded person named Hart; the species is not named for a characteristic of the fish itself.
This fish was long listed as Rivulus harti; Eschmeyer's Catalog of Fishes now treats that name as a synonym of Anablepsoides hartii, the valid name followed here.
Morphology
Hart's rivulus reaches 3.9–4.3 in total length, with published maxima of 3.9 in (FishBase; Smithsonian STRI) and 4.3 in (It Rains Fishes / Vermeulen). The body is slender and cylindrical, tapering to a rounded caudal fin — the typical rivuline build suited to darting through root tangles and shallow margins. The mouth is slightly upturned, consistent with surface-feeding habits and the aerial strikes on prey documented in the field.
Males carry bright orange-yellow margins on the upper and lower lobes of the caudal fin, a reliable sex signal visible at a distance. Body colouration in males is typically more vivid than in females, with greenish to brownish flanks that can show iridescent flecks; females are plainer with a rounded belly and less-marked finnage. Both sexes can reach 3.9–4.3 in, though females in breeding condition are noticeably fuller-bodied. The remarkable tail-vascular anatomy that underpins cutaneous air-breathing is not visible externally but explains the fish's documented tolerance of temporarily hypoxic environments.
Habitat
Hart's rivulus occupies a broad mosaic of permanent and near-permanent water types across the southern Caribbean and adjacent South American mainland. Its native range encompasses Trinidad and Tobago, Grenada, Isla Margarita (Venezuela), and coastal lowlands and foothills of Venezuela and Colombia draining toward the Caribbean. The University of the West Indies (St. Augustine) documents the habitat spectrum as small mountain streams, seasonal rain pools, estuaries, lowland swamps, and rivers, with salinity tolerance spanning fresh to brackish conditions including mangrove fringe waters.
The Smithsonian Caribbean (STRI) dataset records the species at depths of 0–7 ft in estuarine, mangrove, and freshwater settings, often in water with abundant organic matter and leaf litter. Temperature tolerances centre on 72–79 °F (FishBase; UWI), reflecting the relatively stable thermal environment of the Caribbean lowland tropics. The species is diurnal and behaviourally conspicuous, with the capacity to jump and to move short distances overland across wet leaf litter to bypass obstacles — a trait the UWI accounts note makes waterfall barriers effectively permeable to it. This overland ability also accounts for its presence in apparently isolated hill-stream pools above local falls.
Feeding
The UWI (St. Augustine) natural-history account describes a notably broad omnivorous diet. Primary food items include algae, diatoms, plant material, and mineral particles — indicating significant incidental or deliberate consumption of benthic biofilm. Alongside this, the fish is actively predatory, taking aquatic invertebrates, small fish, tadpoles, and insect larvae. In the field it jumps up to 5.5 in to catch aerial prey including insects, a behaviour that bridges the surface and the air in a way unusual even for killifishes.
This dietary breadth makes the fish straightforward to maintain in captivity. It accepts a wide range of small live and frozen foods — artemia nauplii and adults, daphnia, bloodworm, small earthworm pieces — as well as good-quality dried foods of appropriate size. Its predatory tendency means tankmates significantly smaller than itself are at risk; otherwise, aggression toward similar-sized fish is typically limited to male rivalry.
Mating
Anablepsoides hartii is a non-annual plant-spawner. Internal fertilization is reported by the Smithsonian STRI, and It Rains Fishes (Vermeulen) documents the pair spawning daily over an extended period rather than in a single mass event — the hallmark of a non-annual killifish adapted to stable, productive water rather than a seasonal pool under threat of desiccation.
In the aquarium the male courts the female and the pair align briefly at or near the surface or adjacent to a floating spawning mop. Each spawning session produces 5–15 eggs that are deposited on the mop fibres or on fine-leaved plants. The eggs are amber, approximately 0.06 in in diameter (Vermeulen), and slightly adhesive. This daily-small-clutch strategy results in a continuous trickle of eggs over weeks, allowing the aquarist to collect batches incrementally. Males are not excessively aggressive during courtship, but some pursuit does occur; adequate plant or mop cover for the female is advisable.
Breeding
Eggs collected from the spawning mop or plants are incubated in water — not in damp peat — at around 75–79 °F. Vermeulen records an incubation period of approximately 14 days. The eggs require no diapause and no drying period; they are simply maintained in a small container of clean, slightly acid water and checked for development. Infertile eggs cloud and should be removed to prevent fungal spread.
Fry hatch at a functional swimming stage and immediately take newly hatched artemia nauplii (brine shrimp), which Vermeulen identifies as the standard first food. Growth is moderate: the UWI and Vermeulen both record a captive lifespan of up to three years, and Vermeulen notes 4–5 months to sexual maturity — long by killifish standards, consistent with the non-annual life history. The comparatively long lifespan makes this species a rewarding long-term project rather than the one-season annual cycle typical of many ornamental killifishes.
In the aquarium
Hart's rivulus is one of the more accessible and forgiving Caribbean killifishes for the intermediate hobbyist. It tolerates the water conditions it encounters across its wild range — temperatures of 72–79 °F, neutral to mildly acid pH, soft to moderately hard water — and is not demanding about chemistry precision. Its tolerance of mild brackish conditions is unusual among killies and makes it compatible with some coastal-fish setups.
A species aquarium with ample floating plants or a cork-bark surface for cover is the ideal setup; a small group of one male and two or three females works well. Dense surface vegetation mimics the natural habitat and provides spawning sites without requiring separate mops, though hobbyists who want to maximise fry yield will prefer to use dedicated floating mops and collect eggs every few days. Because the fish jumps readily and can move overland, a tight-fitting lid is essential.
This species is rarely offered commercially but has a following in specialist killifish clubs. It is generally kept as a long-term resident rather than a seasonal species, and its three-year potential lifespan means a well-maintained pair will produce eggs over an extended period. Compatible tankmates, if any, should be similarly sized, non-predatory species with matching water requirements.
Conservation
Anablepsoides hartii has not been assessed by the IUCN Red List. Neither the FishBase entry nor the UWI or STRI sources carry a formal IUCN status, and the USGS records it simply as a Caribbean slope species without a listing. Its comparatively wide distribution across Trinidad, Tobago, Grenada, Isla Margarita, and the Venezuelan coast, combined with its tolerance of degraded and disturbed habitats including brackish and semi-polluted estuarine margins, suggests it is not immediately threatened at the species level.
However, the individual stream and hill-pool populations of the northern Venezuelan and island ranges face the same pressures affecting freshwater biodiversity across the Caribbean — deforestation of forested catchments, channelisation and pollution of small coastal streams, and ongoing land conversion. Its ability to tolerate brackish conditions and to move between water bodies overland provides some buffer against localised habitat loss, but this resilience has limits. The species has not been the subject of targeted conservation study, and the absence of a formal IUCN assessment means trends in island and Venezuelan mainland populations are unmonitored.