Taxonomy & naming
Nothobranchius torgashevi was described by the Italian killifish specialist Stefano Valdesalici in 2015. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) is the authority for the valid name, which places the species within the large African annual killifish genus Nothobranchius, family Nothobranchiidae. The genus currently contains well over 80 described species distributed across sub-Saharan Africa, and N. torgashevi falls within the species assemblage centred on the seasonally arid savanna drainage systems of central and eastern Tanzania.
The type locality is the Mhwala River, Lake Eyasi basin, Tanzania. Two collection sites have been recorded under the same AKA/hobbyist code TNT 14-5: Mhwala River and Itigi, both in central Tanzania. The species belongs to a broader radiation of Nothobranchius occupying the internal drainage basins and seasonal floodplain systems of the East African interior, where the annual desiccation cycle has driven the evolution of the diapause life history shared across the genus.
Morphology
Males reach a maximum of 1.5 in standard length; females are smaller, reaching approximately 1.5 in SL. The body form is typical for the genus: deep and slightly laterally compressed, with a rounded snout, an upturned mouth adapted for surface feeding, and large cycloid scales. Meristic data recorded at the time of description include 16–17 dorsal soft rays, 17–18 anal soft rays, and 29 vertebrae.
Male colouration is the diagnostic feature: the flanks carry light blue scales overlaid with a series of orange to red bars across the head and dorsum. The dorsal and anal fins display vivid red spots, while the caudal fin is a uniform red without significant patterning. This combination of blue flanks and boldly marked fins places N. torgashevi among the more ornate members of its genus.
Females are cryptically coloured in the manner typical of Nothobranchius: drab olive-brown or greyish-tan throughout, with no significant pigment pattern, providing camouflage during the brief wet-season feeding period. Sexual dimorphism is strong and consistent across all Nothobranchius, making sexing straightforward in adult fish.
Habitat
Nothobranchius torgashevi inhabits ephemeral pools and temporary marshes in the seasonally arid savanna landscape of the Wembere River drainage, which empties into the Lake Eyasi basin in central Tanzania. The pools are shallow — less than one metre deep — with no aquatic macrophyte growth at the time of collection. The water is turbid and clay-grey in appearance, reflecting the vertisol-type swelling clay substrate characteristic of the area. Recorded water chemistry at collection: pH 8.3 and temperature 77–86 °F — notably alkaline and warm for a Nothobranchius, reflecting the chemistry of the interior East African soda-influenced drainage rather than the soft, acidic conditions that characterise West African annual killifish habitats.
The substrate is the most ecologically significant feature of the habitat: the heavy vertisol clay swells when wet and cracks deeply when dry, and it is in this mud that the eggs are buried and undergo diapause through the dry season. The entire fish community disappears from the surface when the pools desiccate, with only buried eggs persisting in the cracked clay until the next rainy season brings fresh inundation. Pools may be isolated from one another between rains, contributing to the genetic distinctiveness of local populations.
Feeding
Like other Nothobranchius, N. torgashevi is an opportunistic carnivore adapted to a short, intense wet-season feeding window. In nature the diet likely consists of small aquatic invertebrates — zooplankton, chironomid larvae, small crustaceans, and flying insects that fall onto the pool surface — exploited rapidly during the few weeks or months of pool persistence before desiccation.
In captivity the species readily accepts a range of live and frozen invertebrate foods: Artemia nauplii and adults, Daphnia, chironomid larvae (bloodworm), white mosquito larvae, and Grindal worms are all suitable. The upturned mouth typical of the genus is best suited to surface and mid-water prey; sinking pellets are less readily taken than surface-presented live or frozen foods. Feeding regularly with varied live or frozen invertebrates is the standard recommendation among killifish specialists for maintaining condition and encouraging spawning behaviour.
Mating
Nothobranchius torgashevi follows the classic Nothobranchius mating pattern: a polygamous, substrate-diving system in which males compete intensively for access to females during the brief wet-season window. Males are conspicuously coloured and establish loose dominance hierarchies in small pools; courtship is rapid and not elaborate — a male pursues and manoeuvres alongside a female, and if she is receptive the pair dive together into the soft substrate.
The dive is the critical act: the male clasps the female and both fish plunge head-first into the mud or peat, depositing a small number of fertilised eggs at depth with each dive. Spawning continues over the course of the wet season in multiple sessions. Because wild fish live only a few weeks to months in nature — the entire lifespan must fit within the duration of pool inundation — reproductive output per unit time is high and spawning is near-continuous while conditions allow. In an aquarium setting with a peat or coir substrate, pairs will spawn with this same frantic frequency if maintained in good condition.
Breeding
The eggs of N. torgashevi are buried in the mud substrate and enter diapause — a state of suspended embryonic development — to survive the dry season when the pool desiccates and the adult fish die. The dry storage period in nature corresponds to the duration of the dry season in the Wembere drainage, which can last several months. The embryos resume development and hatch when the pool refills with the next rainy season.
In the aquarium the hobby convention is to maintain the species on a peat or coir moss spawning medium in a shallow tray or container. After several weeks of spawning, the medium is removed, the eggs hand-picked or the whole mass gently squeezed dry, and the peat stored in a sealed plastic bag at room temperature (approximately 75–79 °F) for a conditioning period. After 8–12 weeks minimum — longer periods of 14–18 weeks can increase hatch rates and synchrony — the peat is re-wetted with soft, slightly acidic water, and fry begin hatching within hours to days. Fry are large relative to many killies and take Artemia nauplii immediately; growth is rapid. Mortality can be high in the first days if water quality degrades, as the fry hatch in large numbers into a limited volume of water.
In the aquarium
Nothobranchius torgashevi is maintained primarily by killifish specialists rather than the general aquarium hobby. Its small size (males under 2 in), brilliant colouration, and readily observable annual life cycle make it one of the more rewarding Nothobranchius for keepers interested in the biology of diapause species. The IUCN notes that the species is maintained and bred by aquarium hobbyists, though commercial availability is low — it is typically sourced through killifish society egg exchanges such as those coordinated by the American Killifish Association.
Housing is straightforward for a small Nothobranchius: a species tank of 5.5–10 US gal with a tight-fitting lid, dim lighting, tannin-stained or at least non-harsh water, and a peat or coir substrate layer for spawning. Multiple males can be kept together in a larger tank but will spar; a ratio of one male to two or three females is conventional. The alkaline, warm chemistry of the wild habitat (pH 8.3, 77–86 °F) can be replicated, though many keepers report the species breeds readily in neutral, moderately soft water. Because the wild fish is alkaline-adapted, the extreme soft-acidic peat conditions used for West African Nothobranchiids are not necessary and may be counterproductive.
As an annual species, adults decline rapidly after reaching peak colour and condition; the focus of husbandry is producing and storing eggs rather than maintaining long-lived adults. Keepers familiar with the Nothobranchius storage-and-hatch cycle will find N. torgashevi a straightforward, if infrequently available, addition to a collection.
Conservation
The IUCN Red List assessment by Nagy and Watters (2019) places Nothobranchius torgashevi as Vulnerable under criterion B1ab(iii): the estimated extent of occurrence is 2,0 mi² or less, and the population is believed to occupy between one and ten discrete locations — with only one formally confirmed at the time of assessment. The Lake Eyasi basin and Wembere River drainage of central Tanzania are subject to expanding subsistence and commercial agriculture, and the shallow seasonal pools that constitute the species' entire habitat are readily lost to drainage, water diversion for rice cultivation, and conversion of seasonal floodplain to permanent irrigated fields.
The species does not occur in any protected area. Population trend is listed as unknown, reflecting the difficulty of monitoring fish that exist for only a few months of the year as visible adults in remote, temporary water bodies. The small number of known localities and absence of protected-area coverage, combined with agricultural pressure, underpin the Vulnerable listing. Aquarium hobby breeding represents a form of ex-situ insurance but does not substitute for protection of the remaining wild habitat. The discovery of additional populations elsewhere in the Wembere drainage would be significant and is a priority for future field survey work.