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Abstract African cichlids (subfamily: Pseudocrenilabrinae) are among the most diverse vertebrates, and their propensity for repeated rapid radiation has made them a celebrated model system in evolutionary research. Nonetheless, despite numerous studies, phylogenetic uncertainty persists, and riverine lineages remain comparatively underrepresented in higher-level phylogenetic studies. Heterogeneous gene histories resulting from incomplete lineage sorting (ILS) and hybridization are likely sources of uncertainty, especially during episodes of rapid speciation. We investigate the relationships of Pseudocrenilabrinae and its close relatives while accounting for multiple sources of genetic discordance using species tree and hybrid network analyses with hundreds of single-copy exons. We improve sequence recovery for distant relatives, thereby extending the taxonomic reach of our probes, with a hybrid reference guided/de novo assembly approach. Our analyses provide robust hypotheses for most higher-level relationships and reveal widespread gene heterogeneity, including in riverine taxa. ILS and past hybridization are identified as the sources of genetic discordance in different lineages. Sampling of various Blenniiformes (formerly Ovalentaria) adds strong phylogenomic support for convict blennies (Pholidichthyidae) as sister to Cichlidae and points to other potentially useful protein-coding markers across the order. A reliable phylogeny with representatives from diverse environments will support ongoing taxonomic and comparative evolutionary research in the cichlid model system. [African cichlids; Blenniiformes; Gene tree heterogeneity; Hybrid assembly; Phylogenetic network; Pseudocrenilabrinae; Species tree.] 

Freshwater fishes are notably diverse, given that freshwater habitat represents a tiny fraction of the earth's surface, but the mechanisms generating this diversity remain poorly understood. Rivers provide excellent models to understand how freshwater diversity is generated and maintained across heterogeneous habitats. In particular, the lower Congo River (LCR) consists of a dynamic hydroscape exhibiting extraordinary aquatic biodiversity, endemicity, morphological and ecological specialization. Previous studies have suggested that the numerous high-energy rapids throughout the LCR form physical barriers to gene flow, thus facilitating diversification and speciation, generating ichthyofaunal diversity. However, this hypothesis has not been fully explored using genome-wide SNPs for fish species distributed across the LCR. Here, we examined four lamprologine cichlids endemic to the LCR that are distributed along the river without range overlap. Using genome-wide SNP data, we tested the hypotheses that high-energy rapids serve as physical barriers to gene flow that generate genetic divergence at interspecific and intraspecific levels, and that gene flow occurs primarily in a downstream direction. Our results are consistent with the prediction that powerful rapids sometimes act as a barrier to gene flow but also suggest that, at certain temporal and spatial scales, they may provide multidirectional dispersal opportunities for riverine rheophilic cichlid fishes. These results highlight the complexity of diversification processes in rivers and the importance of assessing such processes across different riverscapes. 

Despite the cultural and economic importance of fisheries to communities in the region, the Mfimi is one of the leastwell-documented river systems in the central Congo basin. Here we present a preliminary listing of species collected during two surveys sampling 35 sites along the main channel, in major tributaries, and in some marginal habitats. A total of 2195 specimens representing 141 species were collected and archived at the American Museum of Natural History, New York, and in the teaching collections of the University of Kinshasa. Five species are considered as potentially new to science, and range extensions of numerous species into the Mfimi are recorded. Based on the data presented we conclude that the fish communities in the Mfimi share affinities with those of the Cuvette Centrale to the north, rather than the Kasai basin with which the river is currently connected via an inflow at the Kwa-Kasai junction. 

Two new Phenacogrammus are described from the Ndzaa River, a small left-bank tributary of the Mfimi-Lukenie River in the central Congo basin. They share with P. deheyni, a congener endemic to the Cuvette Centrale to the north, a prominent anterior expansion of the first pleural rib; a feature interpreted here as a synapomorphy diagnostic for this species assemblage. The two new species are readily differentiated from P. deheyni based on differences in pigmentation patterning, a lower number of scales in longitudinal series (26–28 vs. 29–33) and a longer head length (m. 24.9% SL vs. 21.7 and 23.2% SL). Phenacogrammus flexus, new species, is distinguished from all congeners in the possession of 6 (vs. 7) supraneural bones, and a characteristic zigzag pattern of black pigmentation along and below the midline extending from the posterior border of the opercle to the base of the caudal peduncle. While no unambiguous morphological autapomorphies have been located to diagnose P. concolor, new species, it is nonetheless readily distinguished from all congeners, except P. deheyni and P. flexus, in the possession of a prominent anterior expansion of the first pleural rib. It differs from both P. deheyni and P. flexus in the absence of a dominant pigmentation patterning over the flanks and caudal peduncle. Additionally, it differs from P. flexus in a shallower body depth (m. 24.9% vs. 27.0% SL) and in the possession of 7 (vs. 6) supraneurals. 

The ichthyofauna of the Lulua River, a large right bank tributary of the Kasai River in central Africa, is among the most poorly documented in the Kasai ecoregion. To remedy this lack of knowledge, sampling was carried out between 2007 and 2014 along the main channel and in many tributaries. A total of 201 species distributed in 81 genera, 24 families, and 12 orders are reported from the lower reaches of the Lulua. The species richness reported in this study represents a substantially improved documentation of the Lulua ichthyofauna (historically estimated at only 79 species). Here, 129 species are recorded for the first time, bringing the total number of known species to 208. Among these, five have recently been described: Raiamas brachyrhabdotos Katemo Manda, Snoeks, Choca Manda, and Vreven 2018, Distichodus kasaiensis Moelants, Snoeks, and Vreven, 2018, Distichodus polli Abwe, Snoeks, Choca Manda, and Vreven 2019, Epiplatys atractus Van Der Zee, Mbimbi, and Sonnenberg 2013, and Hypsopanchax stiassnyae Van Der Zee, Sonnenberg, and Mbimbi 2015; numerous additional taxa are currently under investigation. Recognized here as a continental hotspot of ichthyofaunal diversity, the Lulua is under extreme threat from exploitation of forest products for building materials, deforestation for shifting agriculture and charcoal exploitation, destructive fishing practices, and mining, all of which are rapidly increasing in the watershed. The present study provides baseline documentation for use in conservation planning and future devel- opmental projects in the Kasai ecoregion in general and Lulua River basin in particular. 

More than 40 years ago in their compendium of fish diversity in the lower Congo River (LCR), T. R. Roberts and D. J. Stewart posed the question, “Why does the LCR harbor so many cichlids?” Here we seek an answer through a synthesis of the last 40+ years of research on cichlid diversity, ecology, and speciation. Our review suggests a key role for the unique geomorphology and hydrology of the river itself and its history of connectivity to other African freshwater ecosystems. In contrast to the river upstream of Pool Malebo, the LCR channel is entirely bedrock, and littoral habitats are mostly rocky and rock-strewn. In situ measurements have recorded dramatic changes in channel topology, fluctuating bed bathymetry, and regions of extreme depth. A combination of high annual discharge, steep elevational decline, and fluctuating channel width and depth result in extraordinarily high energy flow regimes throughout the LCR. In-stream hydraulics and bathymetry appear to play a key role in isolating cichlid populations and are likely powerful drivers for micro-allopatric isolation and speciation, often over remarkably small geographical scales. Moreover, this hydrologically extreme environment is the evolutionary backdrop for an unusual array of cichlid morphologies, including the only known blind cichlid (Lamprologus lethops).