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African cichlids are model systems for evolutionary studies and host-parasite interactions, because of their adaptive radiations and because they harbour many species of monogenean parasites with high host-specificity. Five locations were sampled in southern Lake Victoria: gill-infecting monogeneans were surveyed from 18 cichlid species belonging to this radiation superflock and two others representing two older and distantly related lineages. We found one species of Gyrodactylidae, Gyrodactylus sturmbaueriVanhove, Snoeks, Volckaert & Huyse, 2011, and seven species of Dactylogyridae. Four are described herein: Cichlidogyrus pseudodossouin. sp., Cichlidogyrus nyanzan. sp., Cichlidogyrus furun. sp., and Cichlidogyrus vetusmolendariusn. sp. Another Cichlidogyrusspecies is reported but not formally described (low number of specimens, morphological similarity with C. furun. sp.). Two other species are redescribed: C. bifurcatusPaperna, 1960 and C. longipenisPaperna & Thurston, 1969. Our results confirm that the monogenean fauna of Victorian littoral cichlids displays lower species richness and lower host-specificity than that of Lake Tanganyika littoral cichlids. In C. furun. sp., hooks V are clearly longer than the others, highlighting the need to re-evaluate the current classification system that considers hook pairs III–VII as rather uniform. Some morphological features of C. bifurcatus, C. longipenis, and C. nyanzan. sp. suggest that these are closely related to congeners that infect other haplochromines. Morphological traits indicate that representatives of Cichlidogyruscolonised Lake Victoria haplochromines or their ancestors at least twice, which is in line with the Lake Victoria superflock being colonised by two cichlid tribes (Haplochromini and Oreochromini).

Owing to the largely unexplored diversity of metazoan parasites, their speciation mechanisms and the circumstances under which such speciation occurs – in allopatry or sympatry – remain vastly understudied. Cichlids and their monogenean flatworm parasites have previously served as a study system for macroevolutionary processes, e.g., for the role of East African host radiations on parasite communities. Here, we investigate the diversity and evolution of the poorly explored monogeneans infecting a West and Central African lineage of cichlid fishes: Chromidotilapiini, which is the most species-rich tribe of cichlids in this region. We screened gills of 149 host specimens (27 species) from natural history collections and measured systematically informative characters of the sclerotised attachment and reproductive organs of the parasites. Ten monogenean species (Dactylogyridae: Cichlidogyrusand Onchobdella) were found, eight of which are newly described and one redescribed herein. The phylogenetic positions of chromidotilapiines-infecting species of Cichlidogyruswere inferred through a parsimony analysis of the morphological characters. Furthermore, we employed machine learning algorithms to detect morphological features associated with the main lineages of Cichlidogyrus. Although the results of these experimental algorithms remain inconclusive, the parsimony analysis indicates that West and Central African lineages of Cichlidogyrusand Onchobdellaare monophyletic, unlike the paraphyletic host lineages. Several instances of host sharing suggest occurrences of intra-host speciation (sympatry) and host switching (allopatry). Some morphological variation was recorded that may also indicate the presence of species complexes. We conclude that collection material can provide important insights on parasite evolution despite the lack of well-preserved DNA material.

Recently in Cameroon, two species belonging to Quadriacanthus: Q. anaspidoglaniiAkoumba, Tombi & Bilong Bilong, 2017 and Q. euzetiNack, Pariselle & Bilong Bilong, 2016 have been recorded on gill filaments of Notoglanidium macrostoma(Siluriformes, Claroteidae) in the Memou’ou River (Nyong Basin) and Papyrocranus afer(Osteoglossiformes, Notopteridae) in Lake Ossa, respectively. These records have been considered the result of lateral transfers from Clariidae to a Claroteidae host for the first case (parasitism of N. macrostomaby Q. anaspidoglanii) and from Clariidae or Bagridae to a Notopteridae host for the second (parasitism of P. aferby Q. euzeti). In this paper, the investigation of interspecific relationships among Quadriacanthusspp. parasitizing Clariidae, Bagridae, Claroteidae and Notopteridae in Cameroon resulted in the record of Q. anaspidoglaniifrom N. macrostoma, Q. euzetifrom P. afer, a new record of Q. levequeiBirgi, 1988 from Clarias jaensisin the Nyong River, and the description of Q. barombiensisn. sp. from Clarias maclareniin Lake Barombi Mbo. The newly identified species is characterized by having an accessory piece ending in one small hook and the median expansion of its dorsal bar with two filaments. Phylogenetic analysis based on 28S rDNA sequences confirms that the Quadriacanthusspp. parasitizing gill filaments of non-clariid hosts in Cameroon originate from lateral transfers from clariid fishes, and that Clariidae are ancestral hosts of these monogenean species.

Sebkha Imlili (Atlantic Sahara) is a salt flat with over 160 permanent holes of hypersaline water generated in the Holocene and inhabited by euryhaline organisms that are considered to be relics of the past, including the cichlid fish Coptodon guineensis. We surveyed the fish parasites four times over one year, to i) identify the parasites, and ii) determine possible seasonality in infection patterns. Over 60% of the fish were infected by one to three helminths: an acanthocephalan in the intestine and two digenean metacercariae in the kidney, spleen, liver, muscle, and mesenteries. The acanthocephalan Acanthogyrus(Acanthosentis) cf. tilapiaewas identified morphologically and molecularly; only one digenean (the heterophyid Pygidiopsis genata) could be identified molecularly. Both identified parasites were present throughout the sampling periods; the unidentified metacercariae were present only in summer and fall. Mean intensities, but not prevalence of infection by the acanthocephalan, reflected a biannual pattern of transmission. Infection accrued with fish size, possibly due to cannibalism. Because the water holes include only a few invertebrates, the intermediate hosts of these parasites can be inferred to be the gastropod Ecrobia ventrosafor the digeneans and either the copepod Cletocamtpus retrogressusor the ostracod Cyprideis torosafor the acanthocephalan. This ecosystem appears stable and provides a window into the past, as the acanthocephalan likely switched from freshwater tilapia to C. guineensiswhen the Sebkha formed. However, this is a vulnerable environment where the survival of these parasites depends on interactions maintained among only very few hosts.

Four species of Synodontella, including three new, are reported from three species of Synodontis(S. ocellifer, S. nigrita, and S. velifer) from north-western Côte d’Ivoire. Synodontella melanopteraDossou & Euzet, 1993 was found on the gills of S. nigritaand S. veliferand was already known from the gills of S. melanopterusin Benin and the gills of S. obesusand S. rebeliin Cameroon. The new species are Synodontella speroadoteviin. sp. from S. nigrita(type-host), S. veliferand S. ocellifer, and Synodontella bagoueensisn. sp. and Synodontella akengboin. sp., both from S. velifer(type-host for both), S. nigritaand S. ocellifer. The new species differ from the other species of Synodontellamainly in the morphology of their male copulatory organs (MCO): Synodontella speroadoteviihas a two-part penis (one being a hollow tube and the other a flattened tube); Synodontella bagoueensishas a wide G-shaped penis with a sub-terminal opening; and Synodontella akengboihas a simple narrow J-shaped penis. Synodontella speroadoteviidiffers from Synodontella bagoueensisand Synodontella akengboiin the shape of the dorsal transverse bar, which shows no protuberance, and also in the morphology of the MCO. Synodontella bagoueensisdiffers from the other two species in that it has a dorsal transverse bar that is V-shaped and a G-shaped MCO. Synodontella akengboidiffers from the two other species in having a J-shaped MCO and in the size of its ventral and dorsal anchors which, contrary to the other two species, are almost similar.

Three new species of SynodontellaDossou & Euzet, 1993 are described from two species of Synodontis(Mochokidae) collected from the middle course of the Boumba River (East Cameroon): Synodontella angustupenisn. sp. from Synodontis nummifer, Synodontella longipenisn. sp. and Synodontella simplexn. sp. from Synodontis decorus. These new species are different from the other Synodontellaspecies already described due to their horseshoe-shaped dorsal transverse bars. Synodontella angustupenisdiffers from S. longipenisand S. simplexby the morphology of its penis, a thin tube, and its accessory piece, bifid at its extremity. Synodontella longipenisdiffers from the other two species by the morphology and the size of its male copulatory organ, which is very long. Synodontella simplexdiffers from S. angustupenisand S. longipenisby the shape of its penis, which is simple, and of its accessory piece, with a developed heel. The difference between the dorsal transverse bars of Synodontellaspecies from the Sanaga River in Cameroon (and other localities in Africa), slightly curved, and those from the Boumba River, horseshoe-shaped, makes it possible to separate Synodontellaspecies into two different subgroups. This difference can be explained by a long isolation period of the hosts, living in different river basins, followed by the divergence of the parasite populations (vicariant speciation).