- Title
- A taxonomic revision of the shallow-water species of the genera Lethrinops, Tramitichromis and Taeniolethrinops (Teleostei, Cichlidae) from Lake Malawi/Nyasa/Niassa (East Africa)
- Creator
- Ngatunga, Benjamin Peter
- Date Issued
- 2001
- Date
- 2001
- Type
- Thesis
- Type
- Doctoral
- Type
- PhD
- Identifier
- vital:5347
- Identifier
- http://hdl.handle.net/10962/d1007443
- Description
- In order for the SADC/GEF Lake Malawi/Nyasa Biodiversity Conservation Project to draw out sound strategic management and conservation recommendations to the riparian countries of Malawi, Mozambique and Tanzania, the need and urgency for revising the taxonomy of some of the scientifically and economically important fish groups was accorded high priority. This study is a contribution towards achieving those goals. It is a taxonomic revision of the shallow-water species of the genera Taenioiethrinops, Tramitichromis and Lethrinops. These three genera are grouped as Lethrinops 'sensu lato' in this thesis, corresponding to the definition of Lethrinops prior to the revision by Eccles & Trewavas (1989). All members have a characteristic dentition: the outer teeth in the lower jaw curve inwards posteriorly ending just behind the inner row(s), rather than continuing backwards as a single series, as in most other Malawian haplochromines. The decision to consider shallow-water Lethrinops 'sensu lato' separately from the deepwater ones was not arbitrary, but rather based on available ecological and morphological evidence. Unanticipatedly, on the course of this study, evidence from molecular genetics has helped to strengthen the distinction. Economically, Lethrinops is important for human food and for the aquarium trade. Lethrinops are precocial fish producing very few young at a time and are consequently unlikely to recover quickly from heavy fishing pressure. To evolutionary biologists, Lethrinops 'sensu lato' is challenging because until now most theories about the evolution of Lake Malawi cichlids have not taken the sand-dwelling fishes fully into consideration. A better knowledge of the distribution patterns of these cichlids, of which Lethrinops are the major representatives, can help in explaining the underlying mechanisms of speciation in sand-dwelling cichlids. Lethrinops 'sensu lato' is taxonomically one of the most complex groups of Lake MalawilNyasa haplochromines. The species are closely related and very difficult to differentiate, and the taxonomy is confused and in urgent need of revision. This is more important since taxonomy plays an important role in most of the key criteria of conservation.The principal objective of this study was to carry out a taxonomic revision of this group and to provide a key to the identification of the species. Further objectives include the mapping of their distribution and analysing their phylogenetic relationships. Large samples were collected (by trawling, gill netting, beach seining and purchased from local fishermen) from depths less than 20m and from numerous well-defined localities all around the lake. Seventeen type specimens of the 21 described species of the shallow-water Lethrinops 'sensu lato' were examined and compared with this recently collected material. The data of about 500 fish specimens were subjected to principal component analyses (PCA). To further evaluate morphological differences between taxa of comparable size, non- parametric, distribution-free Mann-Whitney U-tests were used. Within the shallow-water Lethrinops 'sensu lato' three genera are recognized which can be separated by characters such as head shape, pharyngeal morphology and dentition, number and shape of gill-rakers, number of the pectoral fin rays and melanin pattern. So far in this study, 28 taxa have been recognized. The overlapping measurements and meristics compound the difficulty inherent in the identification and classification of members of the three genera. The genera Tramitichromis and Taeniolethrinops are typically shallow- water taxa. Within the genus Taeniolethrinops four described species, (T. cyrtonotus, T.forcicauda, T. laticeps and T. praeorbitalis) were distinguished. Within the genus Tramitichromis nine species were distinguished, five of which are described (T. brevis, T. intermedius, T. lituris, T. trilineata and T. variabilis); four represent undescribed species and are given a working name (T. sp. 'brevis 2', T. sp. 'maculae', T. sp. 'pharyngeals' and T. sp. 'variabilis deep'). For convenience, the shallow water Lethrinops 'sensu stricto' were divided into three natural groups, according to shared morphological features. • The first group is the lethrinus group, including three species (L. lunaris, L. leptodon and L. lethrinus) with relatively lolong snouts and remnants of the horizontal stripes. • Another group included eight taxa (L. microstoma, L. macrophthalmus, L. macrochir, L. auritus, L. parvidens, L. sp. 'parvidens deep', L. 'black dorsal auritus', L. sp. 'domira blotch' and L. sp. 'turneri') with a relatively short snout and a small mouth set low on the profile. Within this group, special attention has been paid to the confusion involving L. auritus and a new species to be described soon, L. sp. 'turneri' . • The last group of Lethrinops 'sensu stricto' is ill defmed and has an intermediate snout and with a lesser round head. Within this group L. oculatus, which was described on the basis of a single specimen, is synonymised with L. marginatus. The other valid species of this group are Lethrinops albus and L.furcifer. Nearly all species seem to have a lake-wide distribution. All are associated with sandy substrata where they feed mainly on insect larvae and ostracods. Mitochondrial DNA sequence data indicate that Lethrinops 'sensu lato' as currently defmed is not monophyletic but is paraphyletic or more probably polyphyletic. It is further suggested that the typical Lethrinops dentition provides no particular strong evidence for affimity among shallow-water Lethrinops s.s., Tramitichromis and Taeniolethrinops. The need for management and conservation of this scientifically exciting group of fishes has been pointed out.
- Format
- 315 leaves
- Format
- Publisher
- Rhodes University
- Publisher
- Faculty of Science, Ichthyology and Fisheries Science
- Language
- English
- Rights
- Ngatunga, Benjamin Peter
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