Emmanuel Vreven

A recent inventory of the fishes of the north-western and central western coast of Lake Tanganyika (Democratic Republic Congo)

Background. Despite the importance of Lake Tanganyikas biodiversity for science and the livelihoods of the riparian people, high-resolution surveys of the fish biodiversity are sparse and fragmentary, especially along the western (Congolese) shoreline. The coast suffers locally from intensive human activities and lacks adequate protective measures or nature reserves. However, in view of the intra-lacustrine endemism of this fish fauna, conservation needs to be managed lake-wide at a fine scale, necessitating detailed inventories on fish species distribution. The study aims at updating knowledge on fish diversity and distribution along the north-western and central western shores of Lake Tanganyika. Materials and methods. Fish specimens were collected using gill-and seine nets, by snorkelling and SCUBA diving, and through purchases on the local markets. Results. Over 28 locations were sampled, and 84 cichlid- and 30 non-cichlid fish species (belonging to Protopteridae, Clupeidae, Cyprinidae, Alestidae, Claroteidae, Clariidae, Malapteruridae, Mochokidae, Poeciliidae, Latidae, and Mastacembelidae) collected. Conclusion. Our records substantially expand the known range of fish species in a range of habitats. As numerous specimens are hard to assign to nominal species, a taxonomic revision of a number of genera is underway. It should take into account intraspecific geographic variation.

A revision of the West African Hepsetus (Characiformes: Hepsetidae) with a description of Hepsetus akawo sp. nov. and a redescription of Hepsetus odoe (Bloch, 1794)

Within the genus Hepsetus, a new species from the eastern part of West Africa is described. Hepsetus akawo sp. nov. is mainly distinguished from Hepsetus odoe by a smaller number of lateral line scales [43–51 vs 50–60 (exceptionally 49)] and a shallower head depth [38.0–45.6 (mean 42.0) % head length vs 41.4–49.0 (44.6) % head length] (positively allometric). Hepsetus akawo sp. nov. differs mainly from the recently rehabilitated Hepsetus cuvieri by: a higher number of gill rakers (17–23 vs 8–13); and a lower number of scales between the dorsal fin and the lateral line (7½–9½ vs 10½–11½). Within West Africa, the distribution area of the new species is restricted to the Sassandra River (Ivory Coast) in the west up to the Cross River (Cameroon) in the east. The species is entirely allopatric with H. odoe, which has a far more restricted distribution than previously thought and occurs from the Senegal River (Senegal) in the west to the Cavally River (Ivory Coast) in the east.

A new mastacembelid species from Lake Tanganyika: a case of complex evolutionary history

A detailed morphometric study of 123 specimens identified as Mastacembelus albomaculatus and the six syntypes of M. tanganicae was undertaken. On each specimen, 27 morphometric measurements and 12 meristics were taken. The type series of M. tanganicae contains more than one species, with four specimens attributed to a new species M. reygeli sp. nov. A redescription of M. albomaculatus and a description of the new species are provided. Both species are endemic to the northern and central part of Lake Tanganyika. They can be distinguished based on the number of caudal vertebrae [47-52 (median 49) in M. albomaculatus v. 42-46 (44) in M. reygeli sp. nov.], the total number of vertebrae [85-90 (88) v. 78-83 (81)] and the distance from the snout to the last externally visible dorsal spine (S-LDS) [61.8-67.0 (mean 64.0) v. 66.6-71.5 (68.6)% L(S)]. In addition, intermediate specimens and populations between M. albomaculatus and M. reygeli were discovered from several parts of the lake, but mainly from the southern part. The latter intermediate populations were provisionally identified as introgressed populations.

A revision of the Lower Guinean Hepsetus species (Characiformes; Hepsetidae) with the description of Hepsetus kingsleyae sp. nov

An α-taxonomic revision of the African pike, Hepsetus odoe, from Lower Guinea is provided. The results show that three different species occur in Lower Guinea instead of one. Hepsetus akawo, recently described from West Africa, is present in the northern part of Lower Guinea; Hepsetus lineata, the most widespread species within Lower Guinea, is known from the Sanaga (Cameroon) in the north to the Shiloango (Democratic Republic of the Congo) in the south and Hepsetus kingsleyae sp. nov. is endemic to the Ogowe Basin. The new species H. kingsleyae is described and H. lineata, which is elevated here to the species level, is redescribed. Hepsetus lineata can easily be recognized by its prominent horizontal line pattern on the flanks and differs further from H. akawo and H. kingsleyae in the number of lateral-line scales and the number of gill rakers. Hepsetus kingsleyae differs from H. lineata and H. akawo by its narrow head, elongated snout and narrow, knife-shaped body. All three species are also distinguishable from H. odoe and the recently revalidated H. cuvieri. A few exceptional specimens could not be allocated to one of the three species and may represent hybrids because of their mixed diagnostic characters or their intermediate values.

Lingering taxonomic confusion in Labeo (Actinopterygii: Cypriniformes: Cyprinidae): correcting the records and basis of type designations for seven Congolese species

Background. The concept of name-bearing specimens is pivotal for nomenclatural stability. Hence, correctly listing the type specimens and designating lectoand neotypes are crucial elements in taxonomic revisions. While reviewing the Labeo Cuvier, 1816 taxa of the Congo basin, we encountered several differences between the lists of type specimens provided in the various revisions of the genus. The majority of problems were encountered with six nominal species of Labeo that were described by Boulenger in 1898: Labeo barbatus Boulenger, 1898; Labeo falcifer Boulenger, 1898 (later replaced by Labeo falcipinnis Boulenger, 1903); Labeo lineatus Boulenger, 1898; Labeo longipinnis Boulenger, 1898; Labeo macrostoma Boulenger, 1898; and Labeo velifer Boulenger, 1898. For four of these species: L. barbatus, L. lineatus, L. macrostoma, and L. velifer, different specimens appear in the literature as name-bearing types. Also for Labeo lividus Roberts et Stewart, 1975, previously a junior synonym of L. barbatus, and for Labeo altivelis Peters, 1852, a species described from the lower Zambezi but also present in the Congo basin, alternative lists of type specimens were mentioned in the literature. Material and methods. The correct list of type specimens was compiled based on museum archives and on an examination of the type specimens. The validity of the lectotype designations was checked. When a lectotype designation proved to be ambiguous, the actions of the subsequent revisers were investigated. Results. We found that the correct lectotypes of L. barbatus, L. falcipinnis, L. lineatus, L. longipinnis, L. macrostoma, and L. velifer are: BMNH 1898.12.28:7, MRAC 17, BMNH 1897.9.30:27, MRAC 113, MRAC 35, and BMNH 1898.12.28:1, respectively. Also for L. lividus and L. altivelis, confusion existed on the type series and a corrected list of type specimens is presented. Conclusion. Especially in older species descriptions, a detailed list of studied specimens is often lacking. In such cases, providing a correct list of type specimens is often not a trivial task. This study shows that inaccurate lists of type specimens can lead to invalid taxonomic acts, which could have nomenclatural implications. We hope that increased efforts in the dissemination of basic taxonomic information will reduce such errors in the future.

Rehabilitation of Bryconaethiops yseuxi Boulenger, 1899 (Characiformes: Alestidae) from the Congo River basin, Africa

Bryconaethiops yseuxi Boulenger, 1899, originally described from “Haut Congo”, is rehabilitated. The species was synonymized, successively with B. microstoma (Günther, 1873) and B. macrops Boulenger, 1920, subsequently rehabilitated, and then again considered as a junior synonym of B. microstoma. Bryconaethiops yseuxi is here considered as a valid species, easily distinguished from all other Bryconaethiops species by its small size (maximum: 72.2 mm SL), 7.5 rows of scales between the dorsal‐fin origin and the lateral line; 11–13/1/8–12 gill rakers on the first gill arch and long dorsal‐fin and anal‐fin bases, respectively, 15.7–17.6% of SL and 22.7–25.9% of SL.

Description of five new rheophilic Orthochromis species (Teleostei: Cichlidae) from the Upper Congo drainage in Zambia and the Democratic Republic of the Congo

Five new rheophilic haplochromine cichlid species are described from the Upper Congo drainage of Zambia and the Democratic Republic of the Congo: Orthochromis mporokoso sp. nov. and O. katumbii sp. nov. from the Bangwelu-Mweru ecoregion, O. kimpala sp. nov. and O. gecki sp. nov. from the Upper Lualaba ecoregion, and O. indermauri sp. nov. from the Lufubu River of the Lake Tanganyika ecoregion. Orthochromis kimpala sp. nov, O. gecki sp. nov., and O. indermauri sp. nov. are distinguished from all currently valid species of the genus Orthochromis Greenwood 1954, except for O. torrenticola (Thys van den Audenaerde 1963), by the presence of eggspots or eggspot-like maculae on the anal fin (vs. no eggspots). The three species can be easily distinguished from O. torrenticola by having three anal spines (vs. four anal spines). Moreover, all five new species can be individually distinguished from all currently known rheophilic taxa placed in the genera Orthochromis, Schwetzochromis Poll 1948 and the rheophilic species of the genus Haplochromis Hilgendorf 1888 (e.g. H. bakongo Thys van den Audenaerde 1964, H. snoeksi Wamuini Lunkayilako Vreven 2010, H. vanheusdeni Schedel et al. 2014) either based on meristic values, morphometric distances and colouration patterns, or on a combination of them.

Don't judge a fish by its fins: species delineation of Congolese Labeo (Cyprinidae)

Conspicuous characters are often useful in species identification. Yet, identification and delineation are two different processes, and such characters do not necessarily provide the best basis on which species can be delineated. This is illustrated by the case of the Labeo with papillary lips from the Congo basin. Traditionally, species delineation in this group was based on a conspicuous trait: the shape of the dorsal fin, which shows a profound degree of differentiation. Morphometric analyses were performed on 185 specimens both with and without measurements taken on this fin. The groups obtained using these two approaches were compared with those obtained through DNA barcoding. For this, 24 sequences of the standard barcoding COI gene were obtained. Species delineations based on morphological and molecular results were in agreement when the shape of the dorsal fin was ignored. This suggested that of the five nominal species known from the Congo basin, L. altivelis, L. rosae, L. lineatus, L. weeksii and L. maleboensis, only the former three remain valid. Consequently, L. weeksii was synonymised with L. altivelis and L. maleboensis with L. lineatus. The sole Congo basin endemic is L. lineatus as L. altivelis and L. rosae also occur in more southern basins. The use of the shape of the dorsal fin in morphological studies has previously led to overestimates of species diversity in this group. This is due to the fact that L. altivelis shows a remarkable amount of geographical variation for this trait. The large amount of intra‐ and interspecific variation in this character was caused by differential allometric growth in different parts of the dorsal fin.

Ichthyofauna of the Itimbiri, Aruwimi, and Lindi/Tshopo rivers (Congo basin): Diversity and distribution patterns

Background. Although the Congo basin is the second largest river basin in the world and it has been considered a biodiversity hotspot for fish, still many parts of this basin remain poorly studied. In this study, we examined the poorly known ichthyofauna of three major north-eastern tributaries of the Congo basin (Itimbiri, Aruwimi and Lindi/Tshopo). A checklist of the ichthyofauna is provided and two synonymies are presented. As such, it contributes to unraveling the poorly known fish diversity in the whole Congo basin. An improved knowledge of the ichthyofauna is a sound baseline for further studies and conservation Material and methods. Fish specimens from five recent expeditions have been identified, and the older collection material from the study area, housed at the Royal Museum for Central Africa and other institutions has been checked and re-identified when necessary. Results. In total, 320 species were recorded, 232 of which from the Itimbiri, 246 from the Aruwimi, and 187 from the Lindi/Tshopo, with the Mormyridae being the most dominant family in all three basins. Micralestes sardina Poll, 1938 is relegated to synonymy with Micralestes humilis Boulenger, 1899, and Enteromius trinotatus (Fowler, 1936) is designated as a replacement name for Enteromius tetraspilus (Pfeffer, 1896). Within the Aruwimi, a clear difference in species richness and composition is apparent between the headwaters (Ituri/Epulu) and the lower reaches near the Congo main stream. The headwaters are characterised by low species richness, with the Cyprinidae being the most dominant family, while the lower reaches are more species rich, with mormyrid species being the most dominant. The presence of two waterfalls on the Ituri/Epulu has a noticeable impact on the fish distribution. Finally, the hypothesis that an ancient connection between the north-eastern part of the Congo basin and the region of the Albertine Rift is still reflected in their present ichthyofauna is not confirmed. Conclusions. This study provides a first checklist of the ichthyofauna in the north-eastern tributaries of the Congo basin, and illustrates the influence of physical barriers on fish diversity and distribution.

A review of the Distichodus antonii assemblage (Characiformes: Distichodontidae) from the Congo basin

The status of the Distichodus antonii assemblage, all large-sized, banded Distichodus species with a brownish-greenish colour pattern from the Congo basin, incorporating Distichodus antonii, Distichodus atroventralis, Distichodus fasciolatus, Distichodus langi and Distichodus mossambicus, has been revised. Distichodus antonii, D. fasciolatus and D. langi are found to be valid species, though the latter has long been considered a possible junior synonym of D. antonii. A detailed redescription for each of these three species is provided. Reports of D. mossambicus from the Congo basin are based on misidentifications; these specimens are assigned to the D. atroventralis complex, a seemingly polyspecific complex in need of further in-depth revision. An identification key to the large-sized Distichodus species from the Congo basin is provided.