Emmanuel Vreven’s research while affiliated with South African Institute for Aquatic Biodiversity and other places

Mouth morphology plays a crucial role in determining the trophic ecology of fish and sometimes underpins important lineage diversification. Freshwater teleost fish species belonging to the genus Labeobarbus, commonly found in Africa, exhibit intra‐ and interspecific variation and differences in the lower jaw occurring within and between species, respectively. Different phenotypes include a curved U‐shape (‘rubberlips’), a straight lower jaw (‘chiselmouth’) and an intermediate morphology known as the smiling phenotype. In some cases, smiling originates from hybridisation between chiselmouth and rubberlips. However, the trophic relationships of different mouth morphologies in the Labeobarbus taxa are still not well understood, particularly in the Congo Basin. Understanding the trophic ecology of Labeobarbus can enhance understanding of adaptive processes in morphologically diverse lineages. This study aims to investigate how differences in mouth morphology among multiple Labeobarbus species in the Luhoho River (Upper Congo Basin) link with different trophic niche uses. We combined information from gut morphometry, gut contents and stable isotope analyses on 202 fish specimens representing six species across four tributaries of the Middle Luhoho. All approaches consistently revealed trophic niche partitioning between chiselmouth and rubberlip species, respectively, more herbivorous/detritivorous and more insectivorous on the omnivory spectrum. In addition, trophic differences were also found between species within each mouth phenotype. Interestingly, the trophic niche of the smiling phenotype differed strongly from those of other phenotypes at all sites except for L. paucisquamatus, for which the trophic niches overlapped in Tchinganda. The pattern of trophic niche of Labeobarbus suggests subtle strategies to partition feeding resources when they occur across a narrow hydrographic scale.

Mormyridae, a species‐rich family endemic to Africa, remains taxonomically understudied. This has been the case for the genus Pollimyrus Taverne, 1971, which hinders further understanding of the distribution, ecology, and conservation of its species. Therefore, an in‐depth morphometric comparison of all currently valid species is carried out using most of the available type specimens. Species delineations were re‐evaluated, and four species new to science described: Pollimyrus ibalazambai sp. nov. (the Luki River, the Democratic Republic of the Congo), Pollimyrus krameri sp. nov. (the Lugenda River, Mozambique), Pollimyrus vanneeri sp. nov. (the Kouilou‐Niari River, the Republic of the Congo), and Pollimyrus weyli sp. nov. (the Buzi River, Mozambique). In this study, Pollimyrus guttatus is confirmed to belong to Pollimyrus, whereas Pollimyrus eburneensis and Cyphomyrus plagiostoma seem more similar to species allocated to other genera. No or only little morphological differences were found between the type series of several species, which could indicate the need for synonymization of these species (Pollimyrus cuandoensis with Pollimyrus marianne and Pollimyrus nigripinnis with Pollimyrus pulverulentus). As such 20 species are currently morphologically identifiable in the genus Pollimyrus. The present study highlights the critical need for further synthetic efforts and new collecting efforts across Africa for this and other Mormyridae genera.

The upper Malagarazi (uM) Basin is situated in Southeastern Burundi and Northwestern Tanzania, and partially covered by the Malagarazi Nature Reserve (MNR). A checklist of fishes from the uM, in Burundi, is presented based on a literature review, a re-examination of historical collections, and a study of new collections (2013–2022). A total of 74 native species, including 14 endemics and two introduced Oreochromis, distributed over 38 genera and 16 families, are reported. Of the aforementioned species, 60 native (81%) and one introduced are present in the MNR. The most important families in the uM and the MNR are the Cyprinidae (21 versus 17 species, respectively) and Cichlidae (12 versus 11). Other families are represented by less than 10 species in both the uM and the MNR. Furthermore, of the 14 species endemic to the uM (19%), only eight (57%) are reported from the MNR; the others are confined to some non-included affluent rivers. Moreover, eight taxa still await formal description. Finally, as some endemic and native species are not included within the current borders of the MNR, adjustments are proposed and the need for a new protected area is considered.

Six populations of morphologically similar Enteromius specimens with a weakly thickened and serrated dorsal spine from the Lowa basin were investigated using an integrative approach including qualitative characters, multivariate morphometrics, and DNA analyses (mtCOI and ncMyh6). These populations are nested within the COI lineage of the E. miolepis species-complex, but differ from all known Enteromius species from the Congo basin, by their dorsal spine morphology, colour pattern, and scale pattern at the dorsal-fin base. In addition, they represent two distinct COI lineages (genetic distance: 5.6–6.1%), with four populations forming a single well-supported lineage described as a new species, Enteromius radari sp. nov. The two remaining populations are sister to the E. miolepis lineage from the Itimbiri. The incongruent position of these two populations in the COI tree may point to past introgressive hybridization events, incomplete lineage sorting, or recent speciation. Analysis of a ncDNA marker (Myh6) did not provide more information due to its slow mutation rate. These results are indicative for introgression or mtDNA capture and provide the first report for such an evolutionary event in Enteromius from the Congo basin.

We sequence (using high thoughput Illumina 150 bp paired-end sequencing) the holotype specimen of mormyrid fish Heteromormyrus pauciradiatus (Steindachner, 1866) to investigate its identity and relationship to the slender stonebashers that are misclassified in genus Hippopotamyrus. We find it to have identical sequences to a lineage of slender stonebasher from the Kwanza and Lucala rivers of Angola previously called "K4." This is a summary presentation of our publication of the same title in ZooKeys, vol. 1129. https://zookeys.pensoft.net/article/90287/

Heteromormyrus Steindachner, 1866, a genus of Mormyridae (Teleostei: Osteoglossomorpha), has been monotypic since the description of Heteromormyrus pauciradiatus (Steindacher, 1866) from a single specimen. No type locality other than “Angola” was given and almost no specimens have been subsequently identified to this species. In order to investigate the relationship of this taxon to fresh specimens collected in Angola and elsewhere, whole genome paired-end sequencing of DNA extracted from the holotype specimen of Heteromormyrus pauciradiatus was performed and a nearly complete mitogenome assembled from the sequences obtained. Comparison of cytochrome oxidase I and cytochrome b sequences from this mitogenome to sequences from recently collected material reveal that Heteromormyrus pauciradiatus is closely related to specimens identified as Hippopotamyrus ansorgii (Boulenger, 1905), Hippopotamyrus szaboi Kramer, van der Bank & Wink, 2004, Hippopotamyrus longilateralis Kramer & Swartz, 2010, as well as to several undescribed forms from subequatorial Africa collectively referred to in the literature as the “ Hippopotamyrus ansorgii species complex” and colloquially known as “slender stonebashers.” Previous molecular phylogenetic work has shown that these species are not close relatives of Hippopotamyrus castor Pappenheim, 1906, the type species of genus Hippopotamyrus Pappenheim, 1906 from Cameroon, and are thus misclassified. Hippopotamyrus ansorgii species complex taxa and another species shown to have been misclassified, Paramormyrops tavernei (Poll, 1972), are placed in genus Heteromormyrus and one genetic lineage from the Kwanza and Lucala rivers of Angola are identified as conspecific Heteromormyrus pauciradiatus . Three additional new combinations and a synonymy in Mormyridae are introduced. The morphological characteristics and geographical distribution of the genus Heteromormyrus are reviewed. The electric organ discharges (EODs) of Heteromormyrus species are to be treated in a separate study.

Parananochromis moutingae, new species, is the first species of Parananochromis to be recorded as endemic to the Congo Basin. It is recorded from the Lefini, Lebomo, and Mayi Ndombe Rivers in the middle Congo. Paranano- chromis moutingae is distinguished from all congeners by a unique combination of the following meristic and morphological characters: three tubular infraorbital bones; a well-developed hanging pad on the pharynx roof; more scales between the dorsal-fin origin and the upper lateral line (5.5-6.5); more small scales between pectoral and pelvic fin insertions (8-10); presence of scales on the chest; more gill rakers on the lower limb of the first gill arch (8-9); more teeth (5-7) on pharyngobranchial 2 of upper pharyngeal jaw; longer snout (32-39 % HL); longer predorsal distance (33.9-36.1 % SL); broader than long lower pharyngeal jaw; straight urohyal spine; and slightly indented ventral margin of the lower pharyngeal keel. Despite concerted efforts, the species has not been collected in the Lefini River since its original discovery in 2008, probably as a result of the installation of a hydroelectric dam, but it seems to subsist in the other two locations. Parananochromis moutingae, nouvelle espèce, est la première du genre qui soit endémique du bassin du Congo. L’espèce est présente dans les rivières Lefini, Lebomo et Mayi-Ndombe dans le Moyen Congo. Parananochromis moutingae se distingue de tous ses congénères par la combinaison unique des caractères méristiques et morphomé- triques suivants : trois infra-orbitaires tubulaire; un coussinet papilleux bien développé de chaque côté du pharynx; nombre élevé d’écailles entre la première ligne latérale et l’origine de la nageoire dorsal (5,5-6,5) ; nombre élevé des petites écailles entre la nageoire pectorale et le point d’insertion de la nageoire ventrale (8-10); la présence d’écailles sur la poitrine; grand nombre de branchiospines sur la partie inférieure du première arc branchial (8-9); nombre élevé de dents (5-7) sur les parties antérieures de l’os pharyngé supérieur; long museau (32-39% Ltête); grande distance prédorsale (33,9-36,1 % LS); l’os pharyngé inférieur plus large que long; pointe de l’urohyal droite; et la marge ventrale de l’os pharyngé inférieur légèrement échancrée. Malgré les efforts de collecte, l’espèce n’a plus été retrouvée récemment dans la rivière Lefini depuis sa récolte en 2008, probablement suite à l’installation d’un barrage hydroélectrique sur la rivière Lefini, mais elle semble subsister encore dans les deux autres localités.