Taxonomy & naming
Alestopetersius smykalai was described by Max Poll in 1967. The valid name as recognised by Eschmeyer's Catalog of Fishes is Alestopetersius smykalai Poll, 1967. Two synonyms circulate in older hobby and trade literature: Hemigrammopetersius smykalai and Rhabdalestes smykalai, both reflecting historical uncertainty about generic placement within the family Alestidae — the African tetras.
The genus Alestopetersius contains a handful of slender, laterally compressed Congo-basin tetras; A. smykalai is anomalous within it because its entire wild range lies in the Niger drainage of Nigeria, not the Congo basin at all. That biogeographic oddity has made the species a subject of ichthyological interest out of proportion to the sparse collecting records that exist for it.
Morphology
The Blue Diamond Tetra reaches around 2.5 in total length, with some sources recording individuals approaching 3 in under optimal conditions. The body is elongate and laterally compressed in typical alestid fashion, with a moderately forked tail and the large eye characteristic of many African tetras.
Colouration is the species' primary appeal. The body is silver to golden-silver with a faint blue-green iridescent sheen along the flanks. Adult males develop a conspicuously elongated dorsal fin with blue pigmentation along its leading rays, and the anal fin carries a white or pale margin that intensifies in dominant fish. A darker marking is often visible at the base of the tail. Females are somewhat smaller, plainer, and lack the elongated dorsal — the sexual dimorphism is clear in mature specimens and is one of the more useful tools for sexing the fish.
Habitat
The species inhabits the lower Niger River and its tributaries in Nigeria. The Niger at this latitude flows through lowland forest and savanna, with seasonal flood-pulse dynamics driving water chemistry and habitat availability. Wild collections have been associated with relatively soft, near-neutral water: temperatures around 70–81 °F and pH approximately 6.0–7.5 depending on season and precise locality.
In common with many smaller African characins, A. smykalai likely shelters among submerged root tangles, marginal vegetation, and riparian debris rather than in open, fast-flowing channels. The restricted and incompletely documented range — fewer collecting records exist for this species than for most Congo-basin alestids — means a precise habitat characterisation remains elusive, but the combination of soft to medium-hard water, moderate temperature, and vegetated or structurally complex microhabitats appears consistent across reports.
Feeding
Alestopetersius smykalai is an opportunistic omnivore, feeding at the surface and in the middle water column. In the wild it takes small invertebrates, insect larvae, terrestrial insects that fall to the water surface, and presumably plant matter and detritus.
In the aquarium it accepts standard aquarium foods readily: quality flake, small pellets, and frozen or live foods such as Daphnia, fruit flies (Drosophila, which Aquarium Glaser's Frank Schäfer notes as a particularly appreciated food), brine shrimp, and bloodworm. A varied diet with regular live or frozen components maintains condition and intensifies the blue dorsal colouration in males.
Mating
Like other alestids, A. smykalai is a free-spawning, egg-scattering species with no parental care. Males display to females and to rival males with spread fins, the elongated dorsal raised and angled to maximise its apparent size, and the pale anal-fin margin flashed as a visual signal. The species is active and fast-swimming, and courtship chases through a well-planted tank are energetic and rapid.
Breeding condition is best maintained by keeping a small group — several males with females — rather than an isolated pair, since the presence of competing males sustains display intensity. Water chemistry for conditioning and spawning should be kept soft and slightly acidic (pH at or below 7.0, hardness below 10° dH) to replicate the low-mineral conditions of the Niger floodplain.
Breeding
Successful spawning in captivity is documented but described as difficult and uncommon. Eggs are reported to be non-adhesive and relatively large — approximately 0.5 in in diameter — deposited near spawning mops placed on or near the substrate, or scattered among fine-leaved vegetation. Reported incubation at warmer breeding temperatures (around 82–84 °F) is approximately 5–6 days, with free-swimming fry appearing a further 4–5 days after hatching.
Hatch rates in captivity are often low (estimates of 20–40 % have been noted), and fry are slow growers — reaching maturity at roughly 6–8 months. First foods for the tiny fry should be infusoria or commercial liquid fry food, graduating to freshly hatched brine shrimp nauplii as the fry grow. Adults must be removed or eggs transferred after spawning to prevent predation. The species is considered rare to breed in the literature, and any documented successful reproduction represents a meaningful contribution to maintaining captive stock of an Endangered species.
In the aquarium
The Blue Diamond Tetra is a challenging but rewarding species best reserved for experienced aquarists. It is sensitive to nitrate accumulation and to poor water quality — diligent maintenance, generous filtration, and regular partial water changes are non-negotiable. The fish is also a confirmed jumper, and the aquarium must be kept covered at all times.
A group of six or more is recommended; the species is skittish when few in number but gains confidence and displays more freely in larger schools. A planted aquarium with dark substrate and subdued lighting shows the species at its best — the iridescent silver-blue flanks and blue dorsal glow under low light in a way that vanishes under bright overhead illumination. Tankmates should be peaceful, similarly sized fish unlikely to fin-nip the males' long dorsal. The species is rarely offered in the trade and is often expensive when available; sourcing captive-bred stock rather than wild-caught imports is strongly preferable both for animal welfare and for the species' conservation.
Conservation
Alestopetersius smykalai is assessed as Endangered (EN) on the IUCN Red List, with the assessment based on its restricted range in the lower Niger drainage combined with documented and ongoing habitat degradation. The Niger River basin faces intense pressures from agricultural runoff, artisanal and industrial pollution, sand mining, and altered hydrology; these pressures are particularly acute in the lowland reaches of Nigeria where this species occurs.
The rarity of the species in both the wild record and the aquarium trade reflects how infrequently it is collected. It is a difficult species to transport — high mortality in transit has been noted — which further limits its presence in the hobby. Captive-breeding programmes in the hands of specialist fishkeepers represent one of the more practical conservation contributions available, given that the wild population cannot be easily monitored or protected. Aquarists who succeed in breeding the species are encouraged to share surplus stock through specialist groups and society auctions rather than returning unsold fish to the general trade.