Taxonomy & naming
Alestopetersius compressus was described in 1963 by Max Poll and Jean-Pierre Gosse. The parenthetical authority reflects the fact that the species was not originally placed in the genus Alestopetersius under which it now stands; Eschmeyer's Catalog of Fishes (CAS) confirms the valid name and records two synonyms: Hemigrammopetersius compressus and Petersius compressus, the latter indicating an earlier placement in the broadly defined Petersius before that assemblage was revised.
The genus Alestopetersius belongs to the family Alestidae, the African tetras, a clade of characoids distributed across sub-Saharan Africa and comprising roughly a dozen genera of mostly small to mid-sized riverine schooling fishes. Alestopetersius is concentrated in the Congo drainage, where its species tend to be associated with large, high-discharge rivers and their lower tributary systems. No subspecies of A. compressus are currently recognised.
Morphology
As the specific epithet suggests, Alestopetersius compressus is noticeably compressed laterally — its body is distinctly flattened from side to side relative to its depth, giving it a blade-like profile that is characteristic of the genus. FishBase records a maximum standard length of 3 in, placing it among the smaller members of Alestopetersius.
The genus shares with other alestids the two-part dorsal fin, a forked caudal, and the adipose fin that marks all characoids. Precise details of colour pattern, squamation, and fin-ray counts for A. compressus are not widely documented in accessible hobbyist literature; available photographs and field records suggest a silvery fish with the typical lateral flank sheen of a schooling Congo tetra relative, though lacking the spectacular elongated finnage of the more familiar Congo tetra (Phenacogrammus interruptus) with which it shares portions of its range.
Habitat
Alestopetersius compressus is endemic to the middle Congo River basin in the Democratic Republic of the Congo. FishBase lists its distribution across the Congo River proper, the Itimbiri, Aruwimi, Lindi-Tshopo, and Lomami river systems, and around Wagenia Falls — a substantial, though geographically coherent, stretch of the mid-Congo drainage.
Field data from the Lake Tumba landscape (Bongo Stream, 2007–2011) shed useful light on microhabitat preferences. The species was strongly dominant at the Bongo Stream headwater site — the most abundant fish there — yet was completely absent during brown-water phases, when the stream's water chemistry and clarity shifted. This pattern suggests a preference for clear-water conditions with stable chemistry, which in the Congo basin typically corresponds to seasonal peaks in river flow from forested catchments rather than backwater or floodplain environments with high tannin and low dissolved-oxygen inputs.
The IUCN assessment notes habitat types as permanent and seasonal inland wetlands — rivers, streams, creeks, and permanent freshwater marshes — across the central Congo basin, with known localities including Yangambi, Buta, and Lac Maindombe. It is classified as a pelagic freshwater species, indicating a preference for the open water column rather than benthic or heavily vegetated microhabitats.
Feeding
FishBase assigns Alestopetersius compressus a trophic level of 3.1, placing it at the base of the secondary consumer range and consistent with an opportunistic diet of small invertebrates, zooplankton, and organic detritus. This is typical for alestids of similar body size; most species in the family are omnivores that shift diet composition opportunistically with season and prey availability.
In the aquarium, analogous Congo-drainage alestids of comparable size accept a wide range of foods: quality flake and micro-pellets form a workable staple, but live and frozen invertebrates — brine shrimp nauplii, Daphnia, micro-worms, and finely chopped bloodworm — improve condition and likely replicate the prey spectrum encountered in the river. Regular small meals suit the active metabolisms of mid-water schooling tetras.
Mating
No published account of courtship behaviour in Alestopetersius compressus specifically is available in accessible sources. Based on the biology of closely related Congo alestids and the family pattern, the species is almost certainly an egg-scattering open spawner: males pursue females through the water column, and fertilised eggs are released non-adhesively into the environment without directed placement on vegetation or substrate.
In riverine alestids, spawning tends to be triggered by seasonal cues — rising water levels, temperature fluctuations, and the influx of oxygenated water that accompanies Congo basin wet-season floods. The complete absence of A. compressus from Bongo Stream during brown-water phases may reflect a seasonal withdrawal from marginal habitats coinciding with or preceding reproductive activity in the clearer channel waters of the main river.
Breeding
Alestopetersius compressus has not been documented as established in the aquarium trade, and specific captive-breeding records for the species are not available in accessible hobbyist or scientific literature. Based on the pattern seen across comparable African tetra genera, breeding in captivity would likely follow the open egg-scattering mode: a group of conditioned adults, a spacious tank with fine-leaved plants or spawning mops, slightly acidic to neutral and moderately soft water, and a dawn-light trigger.
Eggs in egg-scattering alestids are typically non-adhesive, scattered freely among vegetation or over the substrate, and hatch within 24–72 hours at tropical temperatures. Adults offer no parental care and readily consume eggs, so removal of spawning medium or parents after spawning is standard practice. Fry are tiny at hatching and require infusoria or commercial micro-fry foods before graduating to brine shrimp nauplii.
In the aquarium
Alestopetersius compressus is seldom encountered in the aquarium hobby. No commercial supply of tank-bred or wild-caught stock is established in major markets, and the species does not appear in mainstream trade listings. Specialists in Congo basin fishes occasionally obtain wild-caught specimens as bycatch in shipments of other mid-Congo tetras.
If kept, its requirements would follow those of related alestids from clear-water Congo tributaries: a spacious tank with good water movement and oxygenation, slightly acidic to neutral water (pH 6.5–7.5 based on IUCN habitat notes and the clear-water affinity documented at Bongo Stream), temperatures in the tropical range typical for mid-Congo lowland rivers, and a schools of six or more individuals to allow normal social behaviour. The species is pelagic in nature and will use the open water column; dense planting along the margins with open central swimming space suits the family. Compatible tankmates would be other mid-water, similarly sized Congo tetras, small dwarf cichlids, and peaceful bottom-dwellers.
Conservation
Alestopetersius compressus is assessed as Least Concern (LC) on the IUCN Red List, with the assessment published 16 February 2009 by assessor T. Moelants. The listing reflects a species with no recognised major threats, a broad if geographically restricted distribution within the middle Congo basin, and high local abundance where it does occur. No specific conservation actions are noted.
The Congo River basin is the world's second-largest river system by discharge and remains relatively intact compared to many tropical freshwater systems; its fish assemblages face fewer imminent pressures from deforestation or dam construction than equivalent river basins in South and Southeast Asia. The population trend for A. compressus is listed as unknown. High local abundance at specific survey sites — such as Bongo Stream, where it dominated catches — suggests the species is not in decline at a landscape scale, though targeted monitoring data are absent. Its resilience rating on FishBase is recorded as high, consistent with the LC assessment.