Abstract
Synodontis Cuvier, 1816 (Teleostei, Mochokidae) species are often
extremely abundant in local fisheries catches over their entire
distribution range. They are appreciated as food as well as popular
aquarium fishes. However, some species are extremely difficult to
identify due to the taxonomically unreliable nature of prominent
morphological features. Establishing the correct identification is
important and can have far-reaching consequences (e.g. in fisheries,
conservation, stock assessment, and angling records may be
compromised by misidentifying species due to the complicated
nature of present identification keys). The systematic status of
many southern African Synodontis species is poorly understood
and their identification remains problematic. This study involves
characterising the species of the genus Synodontis by comparative
morphological and genetic studies due to the above-mentioned
problems.
Extensive field studies have lead to a simplified identification
key. This key excludes the detail character information included in
the published key that masks the more reliable characteristics.
Synodontis njassae, S. macrostigma, S. macrostoma, S. leopardinus,
S. thamalakanensis, S. woosnami, S. vanderwaali, S. nigromaculatus
and S. zambezensis were used in an allozyme study with
Parauchenoglanis ngamensis as outgroup. Fixed allele mobility
differences were obtained at eight of the 15 loci studied. The
dendrograms grouped all species with convex humeral processes
in one clade. The species with concave humeral processes also
grouped together, but with poor resolution with DNA - sequence
analysis.
A biochemical genetic study of laboratory produced hybrids
between two species of Synodontis was done to provide additional
information on the species boundaries and to determine whether
genetic markers can be found to identify them. Hybrizymes were
found in the latter study. Such markers are of conservation
importance due to the uncontrolled translocation of many exotic
fish species.
This is the first study to evaluate the phylogenetic relationships
of southern African Synodontis species and of hybrids, and the
simplified identification key will be useful for positive identification
of the species studied.
Prof. F.H. Van der Bank