THE NOTHOBRANCHIUS SITE

MSNG 61237, holotype, male, 23.3 mm SL, Kenya: temporary ditch associated with Nyando River floodplain, Lake Victoria basin, 00°09'00" S, 35°00'18" E; 3 Jan 2012, G. Amato, J. Gathua & S. Valdesalici, [field code: KAV 2012-1].

MSNG 61238 (9)

Nothobranchius derhami belongs to the N. ugandensis species group presenting the following combination of characters in males: body coloration light blue with red to red-brown scale margins; frontal part of head red-brown and throat light blue or red; caudal fin uniform red; anal fin light blue or yellow with red-brown spotted pattern. Nothobranchius derhami differs from all other members of the N. ugandensis species group by a dorsal fin with a slender light blue subdistal band and a narrow black distal band; an anal fin with broad subdistal zone cream to yellow, with narrow red-brown to black distal band; and asmaller suborbital depth 16–18 % HL (vs. 19–28) (Nagy et al., 2020).

Subgenus: Zononothobranchius

Species group: N. ugandensis group

​Populations of this species were regarded as part of a diverse complex generally lumped into Nothobranchius species ‘Lake Victoria’, from the basin of that lake in central and western Tanzania and south-western Kenya, together with populations from drainage systems in central Tanzania.

Nothobranchius derhami was described by Valdesalici & Amato (2019) and is known from the Nyando system northeast of Lake Victoria in south-western Kenya. Previously, specimens from this area, in the vicinity of Kisumu, were known from Leakey and Greenwood in the 1950s (Turner, 2009), and the first collected specimen representing this complex to be lodged in a museum was from the Kano Plains in south-western Kenya, associated with the lower reaches of the Nyando River system, by Whitehead in 1966. These specimens are now housed in NHM.

Finally, first identified populations were collected by de Rham from near Ahero in 1985 (de Rham, 1991).

Kenya: temporary ditch associated with Nyando River floodplain, Lake Victoria basin, 00°09'00" S, 35°00'18" E.

This species is endemic to freshwater habitats in south-western Kenya. It is known from ephemeral pools and marshes associated with the Nyando system northeast of Lake Victoria in south-western Kenya.

Lake Victoria basin (521)

1150–1178 m

At the time of type series collection, the type locality substrate was light clay grey and the water turbid, with a pH of 7.6, and at 12:00 the temperature ranged from 25 to 31°C depending on the position in the water column (Valdesalici & Amato, 2019).

Water parameters from further three collecting sites are as follows: temperature of 20–28 °C; pH of 6.8–7.4; conductivity of 60–370 µS; and typically turbid (Nagy & Watters, unpublished data).

None

The species has an annual life cycle.

Embryonic development under captive conditions in peat moss is about three to four months at room temperature.

Maximum size reported: 31.0 mm SL (MRAC 2019.016.P.0059-0067, male)

Diploid chromosome number 2n = 36, NF = 64, karyotype structure 4m+24sm+8st/a (Krysanov et al., 2023).

Karyotype structure unique in the genus, whereas fundamental number unique in the species group.

The specific name is given in honour of Patrick de Rham, Lausanne, Swiss, who discovered the new species on the 7th of July 1985 in a grassy swamp situated near Ahero on the east side of the Nakuru to Kisumu road and for his contribution on observing in the field part of the life cycle of this species. A noun in genitive.

Endangered B1ab(iii)+2ab(iii) (Nagy & Watters, 2021);

Previous assessments: Vulnerable D2 (Hanssens, M. 2004) [as N. sp. nov. 'Lake Victoria']

Recommended at least as Vulnerable D2 (Valdesalici & Amato, 2019)

    de Rham, P. 1991. Safaris poissons au Kenya. Deuxième partie. Aquarama, 121: 21–30. [collecting as Nothobranchius sp. Ahero]

    Valdesalici, S. & G. Amato. 2019. Nothobranchius derhami (Cyprinodontiformes: Nothobranchiidae), a new species of seasonal killifish from western Kenya. Aqua, International Journal of Ichthyology, 25: 111–124. [taxonomy as Nothobranchius derhami]

    Nagy, B. 2020. An expedition around Lake Victoria. Tropical Fish Hobbyist, #744, Sep/Oct 2020, 69 (1): 44–50. [collecting]

    Nagy, B., B. R. Watters, P. D. W. van der Merwe, F. P. D. Cotterill & D. U. Bellstedt. 2020. Review of the Nothobranchius ugandensis species group from the inland plateau of eastern Africa with descriptions of six new species (Teleostei: Nothobranchiidae). Ichthyological Exploration of Freshwaters, 30 (1): 21–73. [phylogeny]

    Nagy, B. & B. R. Watters. 2020. Threatened - the world is a dangerous place for seasonal fishes. Journal of the American Killifish Association, 53 (4): 141–156. [conservation]

    Nagy, B. & B. R. Watters. 2021. Nothobranchius derhami. The IUCN Red List of Threatened Species: e.T158619800A158619803. [conservation]

    Nagy, B. & B. R. Watters, 2021. A review of the conservation status of seasonal Nothobranchius fishes (Teleostei: Cyprinodontiformes), a genus with a high level of threat, inhabiting ephemeral wetland habitats in Africa. Aquatic Conservation: Marine and Freshwater Ecosystems, 1–18. [conservation]

    Krysanov, E. Y., B. Nagy, B. R. Watters, A. Sember & S. A. Simanovsky. 2023. Karyotype differentiation in the Nothobranchius ugandensis species group (Teleostei, Cyprinodontiformes), seasonal fishes from the east African inland plateau, in the context of phylogeny and biogeography. Comparative Cytogenetics, 17 (1): 13–29. [chromosomes]