Taxonomy & naming
Bathyaethiops greeni was originally described by Henry Weed Fowler in 1949, based on material from the Congo drainage; the primary description appears at pages 247–248 of his publication and includes a figure. The parenthetical authority — (Fowler, 1949) — signals that the species was subsequently transferred out of the genus in which Fowler first placed it into Bathyaethiops, where it is recognised today. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) remains the governing reference for the valid name.
The genus Bathyaethiops belongs to the family Alestidae, the African characids, a diverse assemblage of over 100 species distributed across sub-Saharan Africa and including the Congo tetra (Phenacogrammus interruptus) and the tiger fish (Hydrocynus). Bathyaethiops is a small genus of laterally compressed, deep-bodied tetras confined largely to the Congo basin, distinguished within Alestidae by their flattened, disc-like body profile and a distinctive reflective lateral patch. The genus was erected for species that had been shuffled among related genera, and the taxonomy of the group has been subject to periodic revision; Catalog of Fishes is the reference for current placement.
Morphology
Bathyaethiops greeni is a moderately deep-bodied, laterally strongly compressed tetra reaching a reported maximum of 2.5 in total length. The body is relatively high and disc-like in profile — characteristic of the genus — with a rounded snout, large eyes, and a forked tail. The overall coloration is silvery to pale greenish, with the flanks carrying a metallic sheen that can catch the light brilliantly from certain angles.
The species' common name references the round, mirror-like silvery or gold patch on the flank that is a hallmark of Bathyaethiops species, reminiscent of a small moon. Finnage is generally transparent to faintly tinted. As with most alestids, the species possesses an adipose fin between the dorsal and caudal. Sexual dimorphism is not strongly documented in the available literature, though females of deep-bodied characids are typically plumper across the belly when gravid.
Habitat
Bathyaethiops greeni is native to the middle Congo River basin, recorded from the Likouala and Ruki river drainages and the Lake Mai Ndombe drainage system, spanning territory in both the Republic of Congo and the Democratic Republic of Congo. These are lowland, heavily forested waters characterised by slow currents, abundant leaf litter, submerged wood, and often dark, tea-coloured water stained by humic acids from decaying vegetation.
Water chemistry in these habitats tends toward the soft and slightly acidic, consistent with the Congo basin's generally poor, granitic soils. Reported aquarium-compatible parameters centre on pH around 6.9 and moderate hardness (approximately 8–9 dH), with temperatures ranging from 72–82 °F. The lake-associated portions of the range — particularly the shallow, vegetation-rich margins of Lake Mai Ndombe — likely offer calmer conditions with dense aquatic plant growth and drifting leaf material.
Feeding
Bathyaethiops greeni is an omnivore in the wild, feeding opportunistically on small invertebrates, zooplankton, aquatic insect larvae, and vegetable matter encountered in the water column and at the surface. Congo basin alestids of similar size typically exploit a broad dietary range, capitalising on the seasonal productivity of forested floodplain waters.
In the aquarium, the species accepts good-quality flake and small sinking pellets readily, and should be offered regular supplements of frozen or live foods — midge larvae (bloodworm), Daphnia, brine shrimp, and similar small invertebrates — to maintain condition and colour. A varied diet is especially important for bringing fish into breeding condition. It feeds primarily in the middle and upper water column.
Mating
Bathyaethiops greeni is a schooling species with no known parental pair bond. Like most small African tetras in the family Alestidae, it is an open egg-scatterer: males pursue ripe females, and spawning occurs without territorial defence or nest construction. Under good aquarium conditions, conditioning groups of fish together and providing fine-leaved plants or spawning mops replicates the stimulus that triggers natural spawning behaviour.
Spawning has been reported to take place in groups near the substrate, among mosses or on gravel, suggesting that eggs fall or are deposited among bottom material rather than being broadcast into the water column purely at random. Males likely show intensified colour or increased activity during courtship, though detailed field observations are not documented in the available literature.
Breeding
Breeding Bathyaethiops greeni in captivity follows the general pattern for small egg-scattering alestids. Conditioned adults should be offered fine-leaved plants such as Java moss, water sprite, or synthetic spawning mops near or on the substrate, which serve as the egg deposition site. Spawning occurs in groups, and the adults should be removed after spawning concludes as they will consume their own eggs.
Eggs are small and adhesive, and hatch within a few days at tropical temperatures. The fry are initially very small and require appropriately fine first foods — infusoria, paramecia, or commercial micro-fry preparations — before graduating to newly hatched brine shrimp nauplii as they grow. Soft, slightly acidic, warm water (around 79 °F) is generally recommended for breeding attempts with Congo basin alestids.
In the aquarium
Bathyaethiops greeni is a peaceful, somewhat shy schooling fish that should be kept in groups of at least six, and preferably more, to express natural behaviour and reduce individual stress. In smaller groups it tends to be skittish; a larger school allows the fish to settle, swim more openly, and display their reflective flanks to better effect. It is well suited to a community aquarium with other small, peaceful fish from similar biotope habitats.
The aquarium should replicate the shaded, plant-rich conditions of its native forest-stream habitat: a dark substrate, driftwood and dried leaf litter, areas of dense fine-leaved planting, and floating cover to diffuse surface light all help the fish feel secure and show their best coloration. Water should be soft to moderately hard and near neutral to mildly acidic (pH around 6.5–7.2), with temperatures in the 75–82 °F range. Strong current is not required or preferred. The species is infrequently available in the trade but appears occasionally through specialist retailers and importers dealing in Congo basin species.
Conservation
Bathyaethiops greeni is classified as Least Concern (LC) on the IUCN Red List. The species' distribution across multiple drainage systems within the broad middle Congo basin — including the Likouala, Ruki, and Lake Mai Ndombe drainages spanning two countries — provides a relatively wide range buffer compared with range-restricted Congo endemics, supporting its current low-concern assessment.
The Congo basin as a whole faces increasing pressure from deforestation, agricultural expansion, and artisanal fishing, which gradually degrade the slow-water, forested-riparian habitats that species like B. greeni depend upon. While no acute threat to the species is currently documented, continued monitoring is warranted given the rate of land-use change in the region. The low profile of the species in the ornamental trade means collection pressure is minimal.