Taxonomy & naming
Nothobranchius rubroreticulatus was described by Blache and Miton in 1960. The type locality is Koundoul, in the environs of Fort-Lamy — the city now known as N'Djamena — in Chad, at approximately 11°58' N, 15°09' E. The lectotype (MNHN 59.232, 1.5 in SL) is held in the collections of the Muséum national d'Histoire naturelle in Paris. Eschmeyer's Catalog of Fishes (CAS) recognises Nothobranchius rubroreticulatus Blache & Miton, 1960 as the valid name.
The species is placed within the subgenus Zononothobranchius, a grouping defined in part by the reticulated colour pattern shared among several Chad-basin Nothobranchius. Its relationship to the better-known N. rachovii of Mozambique has attracted attention: Seriously Fish notes that molecular (mtDNA) analysis has confirmed N. rubroreticulatus as a valid species distinct from the N. rachovii complex rather than a geographic variant of it. The diploid chromosome number is 2n = 36, consistent with other members of the genus.
The specific epithet combines the Latin rubeo (to be red) with reticulum (net or meshwork), a direct description of the red reticulated pattern on the male's flanks. The genus name Nothobranchius derives from the Greek nothos (false or spurious) and branchia (gills), a reference to the reduced or unusual gill structure characteristic of these killifishes.
Morphology
Males reach approximately 2 in total length (FishBase), making N. rubroreticulatus a typical small-to-mid-sized member of the genus. The body is moderately robust and laterally compressed, deepest at the mid-section and tapering to a narrow caudal peduncle. Females are smaller, drabber, and more uniformly olive-brown.
Male colouration is vivid. The body ground colour is pale blue, with the margins of each scale flushed red-brown; together these create the dense reticulated pattern the specific epithet commemorates. The dorsal, anal, and caudal fins carry the same colour theme — light blue with dense red patterning — with a pale blue subdistal band and a black distal band across all three. This multi-banded fin pattern, combined with the full-body reticulation, distinguishes males from many syntopic or allopatric congeners.
Females are cryptically coloured in olive-brown to grey-brown, with little or none of the male's blue or red pigmentation. The difference is pronounced enough that the sexes can be separated at a glance, even in juveniles approaching sexual maturity.
Habitat
Nothobranchius rubroreticulatus occupies seasonal pools, seasonal swamps, flooded ditches, and temporary water bodies associated with the Chari River drainage, the Bahr Salamat drainage, and the Wadi Al Ghallah drainage — all within the greater Lake Chad basin. Its known distribution spans northern Cameroon, southern Chad, and a fringe of southwestern Sudan, at elevations between approximately 292 and 1565 ft above sea level. These are Sahelian and Sudanian savanna environments: rainfall is strongly seasonal, pools form during the wet season and disappear entirely in the dry months, and the fish must complete its entire life cycle before the water disappears.
Water chemistry data collected in the field by WildNothos researchers records temperatures of 70–72 °F, pH 6.7–6.8, and conductivity of 180–260 µS/cm. The water is typically turbid, carrying suspended clays and organic matter that reduce visibility. The substrate is soft mud and detritus — the medium into which eggs are deposited and in which they undergo diapause through the dry season. Emergent and marginal vegetation is present but the defining feature of the habitat is its impermanence: every pool in the range dries out completely at least once per year.
Feeding
Like other Nothobranchius, N. rubroreticulatus is a microcarnivore in the wild, feeding on the small invertebrates — insect larvae, small crustaceans, zooplankton, and worms — that proliferate in the productive seasonal pools it inhabits. These pools are rich in organic matter and support dense invertebrate communities during the wet season, providing food in abundance for the short period the fish is alive.
In the aquarium, the species accepts live and frozen foods readily. Daphnia, artemia, mosquito larvae, and small bloodworms are all appropriate and eagerly taken. Prepared and dried foods are accepted by acclimated fish, though live or frozen items produce better colouration and conditioning. Given the short lifespan of annual killifishes, consistent, high-quality feeding is more important than it might be for longer-lived species: conditioning the breeding pair well in advance of spawning improves both egg output and egg viability.
Mating
Nothobranchius rubroreticulatus is an annual killifish with substrate-spawning reproductive behaviour typical of the genus. In nature, spawning occurs as soon as pools fill and temperatures and food availability are adequate — the fish must reproduce rapidly, because the pool may last only weeks to a few months before drying again. Males display vigorously to females and to rival males; the vivid reticulated pattern and banded fins serve as both mate-attraction signals and rival-deterrence signals.
Spawning is an act of pair diving: the male courts the female with lateral displays and then the pair dive together into the soft substrate — peat, mud, or detritus — where the female deposits individual eggs that are fertilised by the male in the moment of the dive. The eggs are buried just below the surface of the substrate, each one left in place as the pair resurfaces. This process is repeated many times over the course of a spawning session. The pair do not guard the eggs or invest further in any form of parental care.
Breeding
The eggs of N. rubroreticulatus undergo diapause — a state of arrested embryonic development — that allows them to survive the complete desiccation of the habitat. FishBase and WildNothos report an embryonic development period of approximately 5–7 months at room temperature when the eggs are stored in moist peat moss in the manner practised by the hobby. In nature the eggs remain buried in the cracked substrate through the dry season and resume development when the rains recharge the pool. Hatching is triggered by the re-wetting of the substrate, and fry appear in numbers within days of a pool refilling.
In captivity, the standard annual-killi protocol applies. A pair or group is spawned over a layer of peat or coconut coir substrate several centimetres deep in the aquarium base. After two to three weeks of active spawning the substrate is removed, lightly squeezed to reduce excess moisture, sealed in a plastic bag or container with a label noting the date and species, and stored at room temperature (approximately 72–77 °F) in darkness for the duration of the diapause period — typically five to seven months for this species. At the end of the storage period the substrate is re-wetted with soft water and fry appear within 24–72 hours. First foods are infusoria or commercial micro-fry food, graduating quickly to newly hatched artemia nauplii as the fry grow. Annual killies grow rapidly and typically reach sexual maturity within 6–8 weeks of hatching.
In the aquarium
Nothobranchius rubroreticulatus is well suited to the specialist annual-killifish keeper and is not a fish for a standard community tank. Males are territorial and aggressive toward one another; a single male with one or two females per tank is the safest arrangement, though a colony can be maintained in a larger aquarium with sufficient sight-line breaks. Because the fish is short-lived — typically under a year in the wild, and rarely much longer in captivity — the emphasis in husbandry is on health, condition, and getting the breeding cycle right rather than on long-term maintenance.
The aquarium can be modest in size: a tank of 10–15 US gal is adequate for a pair. Water should be soft to slightly hard, slightly acidic to neutral (matching the field-recorded pH 6.7–6.8), and warm (72–79 °F). A peat substrate or a layer of coir for spawning is essential. Décor of dark sand or fine gravel, leaf litter, and a few plants adds to the fish's sense of security and shows the male's colour to best effect. Filtration should be gentle — the fish come from still to slow-moving water and strong currents are stressful.
WildNothos, the American Killifish Association, and other specialist groups maintain records of this species and can be valuable resources for obtaining eggs or fish from reliable lines. The hobby trades in eggs stored on peat, and obtaining eggs from a reputable source is usually the easiest entry point.
Conservation
The IUCN Red List assessed Nothobranchius rubroreticulatus as Near Threatened (NT) in 2019 (Nagy & Watters), under criterion B2ab(iii). The area of occupancy (AOO) is estimated at 311 mi² or less, and the species is known from only four threat-defined locations, with a projected maximum of approximately 15 known sites. Its extent of occurrence (EOO) is approximately 93,137 mi², but within that broad outline the actual occupied habitat — seasonal pools and swamps on the Sahelian fringe — is fragmented and limited.
The primary threats identified by the assessment are habitat degradation driven by land-use change across the Sahel, and the increased severity and duration of drought episodes linked to climate variability. Sahelian seasonal wetlands are under pressure from expanding pastoralism, dryland agriculture, and human water extraction, all of which reduce the extent and reliability of the temporary pools the species depends on. Unlike some other Nothobranchius that occur in protected areas only peripherally, some populations of N. rubroreticulatus fall within Zakouma National Park in Chad, which provides a degree of in-situ protection.
The Near Threatened status reflects a genuine concern: the species' AOO is well below the thresholds that would trigger Vulnerable listing, and the trend in habitat quality across the range is negative. Annual killifishes are inherently vulnerable because their existence depends on temporary water that is highly sensitive to changes in rainfall patterns. The combination of a restricted AOO, known decline in habitat condition, and the fragility of the annual-pool ecosystem makes N. rubroreticulatus a species deserving continued monitoring.