Chromaphyosemion bitaeniatum
Chromaphyosemion bitaeniatum, the Two-Banded Aphyosemion, is a non-annual killifish native to the coastal lowlands of tropical West Africa, from southern Togo to northern Gabon. I've acquired fish from the population at Ijebu Ode, a city in southwestern Nigeria.
Chromaphyosemion bitaeniatum occurs in small streams and rivulets in a broad stretch of flat coastal plain from the eastern edge of the "Dahomey gap" in coastal rainforest west of Togo to northern Gabon. In small streams feeding the Niger, the species occurs farther upriver, but large rivers form barriers to populations of these rainforest-requiring fishes that are as effective as stretches of sun-baked savanna. With such a broad distribution, in such small, isolated waters, genetic differentiation can be expected to occur: the range of local populations is shown in a gallery of photos at the Deutsche Killifisch Gemeinshaft site. In about half the range of Chromaphyosemion, C. bitaeniatum is the sole member of the genus. The most interesting thing about C. bitaeniatum's distribution is the light it sheds on the pattern of isolated stretches of rainforest that created refugia within the expanding savanna grasslands that characterized West Africa during dry climate phases of the recent Ice Age. The highest diversity among C. bitaeniatum populations is centered in western Cameroon, representing a very recent recolonization of rainforest habitat that these fish require, which was expanding following the end of the ice age. Today, rainforest is rapidly becoming reduced to disjunct patches again, as Nigeria's human population explodes and rainforest gives way to unplanned townlands, local agriculture and secondary scrub.
C. bitaeniatum 'Ijebu Ode' is likely to be preserved in captive populations for its rare beauty, which is outstanding in a genus of great beauties. But other populations of West African killifish, whether they are plainer in visual appeal or more difficult to maintain, are likely to be lost forever in the next decades, along with the historic genetic information they carry. Or their genetic information may become blurred in aquarium strains; my first killies were Aphyosemion gardeneri, just such an aquarium strain, which didn't represent any specific collecting location. Within the monophyletic group of species that were separated from Aphyosemion, there are varying degrees of reproductive isolation among populations; mixing populations in breeding stock may result in infertility in the second generation, according to J.J. Scheel, writing on Rivulin studies for the Musée Royale de l'Afrique Centrale's Annals, 1974. Karyotypes of Chromaphyosemion species differ greatly: C. bitaeniatum's chromosome number is 2n = 40, according to Volker, Rab, Kullman, "Karyotype differentiation" (2008).
The German ichthyologist Ernst Ahl first described this species (as Fundulopanchax bitaeniatus) in 1924. The group of closely related species that were formerly considered part of Aphyosemion was set apart as a sub-species by A.C. Radda (1971) and subsequently raised to species level, as Chromaphyosemion.
C. bitaeniatum is considered easy to keep, at a prefered temperature of 74 - 76oF. Its incubation period is 10 days.
Links. Bill Drake described maintaining C. bitaeniatum for the Preston and District Aquarium Society newsletter.
J.-F. Agnese et al., "Phylogenetic relationships and phylogeography of the Killifish species of the sub-genus Chromaphyosemion (Radda 1971) in West Africa, inferred from mitochodrial DNA sequences" Read the introductory abstract, then skim the technical part, and read the concluding Discussion.
Aphyosemion bitaeniatum at FishBase.
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