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study. Ten localities are known in the
hobby and all populations are very
similar. There are, to date, only three
collections in museums. This is the
only Aphyosemion s. l. species on the
IUCN Red List. This because of its
small distribution region in the upper
Lékoni-Djouya and the upper Mpassa in
the Ogooue basin in southeast Gabon.
The occurrence of this species has been
heavily affected by pollution of the
waters in the vicinity of Franceville
and deforestation leading to increased
sedimentation.
Aphyosemion schioetzi (Huber &
Scheel 1981) is the only representative
of the A. elegans group in the lower
Congo to the north of the river. Its
distribution is limited to an area measuring
around 62 x 62 miles (100 x 100
km), with the majority of known populations
in the DRC and two (including
the type locality) in the Congo Republic.
We do not concur with many other
authors that this species also occurs in
the northern Congo with a distributional
gap of more than 259 miles (400
km) (see A. chauchei), but suggest that
a further, probably still undescribed
Aphyosemion species is involved, shown
on the map as A. “schioetzi.” Aphyosemion
schioetzi populations exhibit a
relatively uniform color pattern, unlike
the related species A. cognatum, in
which numerous different phenotypes
are known.
Aphyosemion schoutedeni (Boulenger
1920) has hitherto been assumed to
be restricted to the type locality Medje,
around 186 miles (300 km) northeast
of Kisangani in the northeast of the
DRC. Although the types are in good
condition, all traces of coloration have
disappeared. But to the present day,
topotypes collected by Lang and Chapin
in 1910 have retained their color pattern
(Van der Zee & Huber 2006),
which resembles that of A. castaneum
except for the pattern of the anal fin.
This color pattern is found in various
RMCA Aphyosemion collections that
originate from the Aruwimi basin east
of the Kisangani-Buta road. Hence it
can be assumed that the distribution
region is significantly larger than previously
thought.
Taxonomy in upheaval: the genus Aphyosemion
DNA studies indicate that the genus Aphyosemion is a complex assemblage
of genetically clearly distinguishable species groups and isolated
species. So far only the most obviously distinct species groups have
been described as genera or subgenera (eg Chromaphyosemion, Kathetys,
Diapteron, Episemion, Raddaella). On the other hand, right from
the start the subgenus Mesoaphyosemion was the “rubbish bin” for all
the difficult-to-classify species and species groups.
And therein also lies a problem with the taxonomy of Aphyosemion
s. l. Humans, as sight-oriented animals, can very easily appreciate the
definition of Chromaphyosemion or Diapteron, as the species within
these groups are very similar, but exhibit clear differences from other
Aphyosemion. This is less apparent with other groups, for example
the “A.” wildekampi and “A.” cameronense species groups. Molecular
genetic studies indicate, however, that phylogenetically speaking, the
visually very distinct species groups are not necessarily more genetically
distant from one another.
Now there are two taxonomic possibilities here: either accept
that the other species groups also represent separate genera, just like
Diapteron, Episemion, and others. Or put them all in a genus Aphyosemion
s. l. with numerous subgenera. But that doesn’t solve the
problem of the species groups so far without any name, whether as
subgenus or genus.
From a pragmatic viewpoint a catch-all genus Aphyosemion provides
less information content than Diapteron or Chromaphyosemion,
for example. For practical purposes it is all the same whether we use
species-group names (e.g., the Aphyosemion bivittatum or A. georgia
group) or scientific names (Chromaphyosemion, Diapteron) for the
different groups. A species group equates to what some authors call
either a subgenus or genus. Hence, as far as the aquarium hobby is
concerned we can regard the terms “species group,” “subgenus,” and
“genus” as essentially equivalent.
Just as with the species groups, it is often the case at species level
as well that usually the most distinctive species are described first. A
good example is the A. cameronense species group or Mesoaphyosemion:
populations are termed M. cameronense that do not have a particularly
distinctive body coloration, that is, have metallic blue to blue-green on
the sides of the body, overlain with a very variable red pattern. Several
obviously different phenotypes have been described in recent decades,
for example M. amoenum and M. halleri, which both have a yellow
caudal peduncle, and M. maculatum and M. mimbon, which possess
a spotted pattern on the sides. Genetic studies indicate that many of
the blue forms of M. cameronense are just as different genetically as the
phenotypically more distinct, described species. Here, too, there are
two solutions: lump everything together in the species M. cameronense,
which would be to ignore major genetic and phenotypical differences
between the phenotypes, or retain the existing species and acknowledge
that M. cameronense as currently understood represents a species
complex. It is for precisely such situations that the use of the aforementioned
locality codes is important, because that way name changes
can be understood, regardless of where these fishes belong taxonomically
and where they come from.
AMAZONAS
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