Taxonomy & naming
Procatopus aberrans was described by the German ichthyologist Ernst Ahl in 1927, with the type locality recorded as Ossiding near Eyomojok in southwestern Cameroon. The genus Procatopus belongs to the family Poeciliidae (sensu lato) under current FishBase placement, or is treated within the lamprichthyid or aplocheiloid lineage depending on the authority — it sits firmly in the non-annual lampeye assemblage regardless of the family boundary applied. Eschmeyer's Catalog of Fishes records Procatopus aberrans Ahl, 1927 as the valid combination.
The genus name Procatopus combines the Greek pro- (before, in front) and catopus from kata (downward) and pous (foot), alluding to the position of the paired fins. The specific epithet aberrans is Latin for 'wandering' or 'deviating', likely reflecting the species' divergence in some character from the type species of the genus. In the aquarium hobby the fish is sold under the common name Blue-green Lampeye, describing the male's vivid body colouration and the iridescent eye-organ.
Several named populations are recognised in the hobby, including fish from Adoro (Anambra drainage, Nigeria), Kumbe, the Osse River (Nigeria), and a DKG Red form, as well as the nominate Ossiding-area fish. Aquarium Glaser notes that specimens labelled P. nototaenia from Yabassi, Cameroon, are sometimes considered an undescribed species rather than a separate valid name, and hobbyists are advised to maintain population lines separately.
Morphology
Procatopus aberrans is among the larger lampeye species, with males reaching approximately 2.5 in total length and females remaining somewhat smaller, typically up to 1 in shorter than males. The body is slender and moderately compressed, typical of surface-oriented killifishes. Meristic counts recorded by the American Killifish Association are D7–8, A15–16, with a lateral line scale count of approximately 30; the karyotype is n=25.
Male colouration is the primary ornamental draw: the body carries a deep, partially iridescent blue to blue-green sheen that intensifies under strong lighting and during display. Above the eye sits the diagnostic lampeye light organ — a crescent of bright, iridescent blue-green photophore tissue that catches the light and gives the genus its common name. Fin colouration includes transparent to lightly tinted rays. Females are considerably plainer, showing a more olive or silvery-brown body with reduced iridescence and a much less conspicuous eye-organ.
Habitat
The natural range of Procatopus aberrans spans southwestern Cameroon (Cross River drainage) and Nigeria (Niger and Benue river basins), according to FishBase. Within that range it inhabits small rivers and brooks under forest cover, forested-savannah transition zones, and streaming creeks — clear, well-oxygenated water with moderate to good flow and surface access. Populations are found in both true rainforest streams and in the more open creeks typical of the forest-savannah ecotone.
FishBase records water temperatures of 75–79 °F and a pH band of 6.5–7.2, reflecting the moderately soft to neutral, warm conditions typical of West African forest and savannah-edge streams. The fish is a surface and upper-water-column species, living near and below the water surface rather than in the benthic zone. AKA records note that the Adoro population (Anambra drainage) comes from typical forested savannah habitat, while other Nigerian localities extend into the Osse River watershed.
Feeding
Procatopus aberrans is an opportunistic micro-predator feeding primarily at and near the water surface. In the wild the diet consists of small invertebrates — aquatic insect larvae, emerging insects, small crustaceans, and zooplankton — items typical of surface-feeding killifishes of clear West African streams.
In the aquarium the species accepts a wide range of small live and frozen foods: Daphnia, Cyclops nauplii, small bloodworm, and micro-worm are all relished. Dry foods are taken from the surface once the fish are acclimatised, though a varied diet with live or frozen invertebrates maintains the best colour and condition. The relatively small mouth constrains prey size; foods should be sized appropriately for a 2–2.5 in fish.
Mating
Procatopus aberrans is a non-annual killifish with no diapause stage. Rather than the explosive, season-compressed spawning of annual peat-burying species, aberrans spawns continuously throughout the year in permanent water, producing modest clutches at regular intervals. The mating system involves courtship displays in which males use their iridescent blue-green body colour and the conspicuous light-organ above the eye to attract females — the lampeye organ is believed to function as an intraspecific signal in the dimly lit, shaded stream habitat.
Spawning is triggered by proximity to suitable egg-deposition sites. Females produce approximately 10–20 eggs per week rather than a single large clutch, reflecting the continuous-spawner strategy typical of permanent-water lampeyes. The AKA records that unlike many killifish that scatter eggs in fine plants, aberrans deposits eggs in fissures and crevices near or at the water surface — using cork bark, rough wood surfaces, and gaps in stones — and females eject eggs with some force so that they adhere in these sheltered spots just at or slightly above the water surface.
Breeding
Eggs of Procatopus aberrans are adhesive and carry the long filaments typical of plant-spawning killifish egg morphology (as noted in Tropical Fish Hobbyist coverage of African plant-spawning killies), anchoring them to the substrate surface. Incubation lasts 12–20 days depending on temperature across the range of 68–79 °F. Fry hatch at night and are quite small, beginning feeding on infusoria and Cyclops nauplii immediately. The AKA records that growth is slow relative to many killifishes: the fish mature at approximately 12 months and are long-lived for a killifish, reaching 4 years under good aquarium conditions.
For aquarium breeding, a species tank with pairs or a small group (one male, several females) is most productive. Cork bark or coarse wood with natural crevices at the water surface provides the preferred spawning substrate. Spawned eggs can be left in the tank if there is adequate cover for fry, or the cork bark can be removed and incubated separately in a shallow dish. Water temperature in the lower part of the natural range (72–75 °F) slows development and tends to produce more robust fry. First foods must be very small — infusoria, commercial fry food, or newly hatched Artemia nauplii once the fry have grown enough to take them.
In the aquarium
Procatopus aberrans is a peaceful, schooling species best kept in a group of six or more individuals. It is an ideal companion for other small, peaceful West African fishes of similar water requirements, and is docile enough for community setups provided tankmates are not so large as to threaten it. The characteristic upper-water-column position means that mid- and bottom-dwelling species make good companions with minimal competition.
Aquarium conditions should replicate the clear, moderately soft to neutral, warm forest-stream environment: temperature 75–79 °F, pH 6.5–7.2, good surface movement, and excellent water quality. Subdued lighting or a tank planted with floating vegetation suits the species' preference for shaded surface zones. The tank should be tightly covered — like all killifishes, aberrans is a capable jumper. Population integrity matters to hobbyists: because several named locality forms exist (Adoro, Kumbe, Osse, Ossiding, DKG Red), it is considered good practice within the killifish hobby to maintain each form separately and label offspring with their origin to avoid diluting distinct genetic lines.
Conservation
The IUCN Red List assessed Procatopus aberrans as Least Concern (LC) in September 2019, reflecting its relatively broad distribution across the Cross River system in Cameroon and the Niger and Benue drainages in Nigeria, and the absence of evidence for a rapid population decline meeting threatened thresholds. The species occupies multiple river systems and is not a single-locality endemic, which provides some buffer against localised habitat loss.
Nevertheless, the West African forest zone that the species depends on faces ongoing deforestation, agricultural conversion, and water extraction pressure. Stream-shading forest cover directly affects the cool, clear, well-oxygenated micro-habitats that lampeyes require; removal of riparian forest degrades water quality and raises temperatures beyond the species' tolerance. Within the killifish hobby, Procatopus aberrans is not widely kept and hobbyist populations are maintained across only a handful of specialist collections, most tied to specific locality codes. Sustaining aquarium breeding lines — particularly for the less common locality forms such as Adoro and Osse — has value as a hedge against the erosion of wild population genetic diversity, even for a species currently assessed as LC.