Jos Snoeks

Royal Museum for Central Africa, Tervueren, Flanders, Belgium

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Publications (85)208.93 Total impact

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    ABSTRACT: Peripheral isolated populations may undergo rapid divergence from the main population due to various factors such as a bottleneck or a founder effect followed by genetic drift or local selection pressures. Recent populations of two economically important Copadichromis species in Lake Malombe, a satellite lake of Lake Malawi, were neither genetically nor morphometrically distinct from their source populations in the main lake. Evidence was found for a founder effect which had a different impact on the genetic composition of the two species. In addition, the increased fishing pressure in Lake Malombe may have led to a reduction of the body sizes of both species. Intra-specific genetic and phenotypic differentiation in two Copadichromis species from Lake Malawi and its satellite Lake Malombe.
    Full-text · Article · Jan 2016
  • Eva Decru · Jos Snoeks · Emmanuel Vreven
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    ABSTRACT: A taxonomic evaluation was made of the Congolese Hepsetus based on 13 counts and 36 measurements on 158 specimens. Within the Congo basin, three species were found: H. lineatus, mainly a Lower Guinean species, is present in the Dja and other parts of the Sangha, but is also recorded in other parts of the Middle Congo (Lilande and Boende); H. microlepis occurs in large parts of the Congo basin, but is absent from the Dja and the southern part of the Kasai, and found also outside the Congo basin in the Gribingui (Chad basin); and H. cuvieri, which is common in the southern part of the Congo, is also present in the Quanza, Cunene, Zambezi and Okavango. Hepsetus odoe microlepis is elevated to species level. This species is characterised by its uniformly blackish colour. It is distinguished from H. odoe, H. kingsleyae, H. lineatus and H. occidentalis by its higher scale row numbers between the dorsal fin and the lateral line, and between the adipose fin and the lateral line; from H. cuvieri, H. kingsleyae and H. occidentalis by a broader head and snout; and from H. lineatus by a shorter dorsal-adipose distance and a higher number of gill rakers.
    No preview · Article · Nov 2015 · Ichthyological Exploration of Freshwaters
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    ABSTRACT: The stunning diversity of cichlid fishes has greatly enhanced our understanding of speciation and radiation. Little is known about the evolution of cichlid parasites. Parasites are abundant components of biodiversity, whose diversity typically exceeds that of their hosts. In the first comprehensive phylogenetic parasitological analysis of a vertebrate radiation, we study monogenean parasites infecting tropheine cichlids from Lake Tanganyika. Monogeneans are flatworms usually infecting the body surface and gills of fishes. In contrast to many other parasites, they depend only on a single host species to complete their lifecycle. Our spatially comprehensive combined nuclear-mitochondrial DNA dataset of the parasites covering almost all tropheine host species (N = 18), reveals species-rich parasite assemblages and shows consistent host-specificity. Statistical comparisons of host and parasite phylogenies based on distance and topology-based tests demonstrate significant congruence and suggest that host-switching is rare. Molecular rate evaluation indicates that species of Cichlidogyrus probably diverged synchronically with the initial radiation of the tropheines. They further diversified through within-host speciation into an overlooked species radiation. The unique life history and specialisation of certain parasite groups has
    Full-text · Article · Oct 2015 · Scientific Reports
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    ABSTRACT: This study evaluates the utility of DNA barcoding to traditional morphology-based species identifications for the fish fauna of the north-eastern Congo basin. We compared DNA sequences (COI) of 821 samples from 206 morphologically identified species. Best Match, Best Close Match and All Species Barcoding analyses resulted in a rather low identification success of 87.5%, 84.5% and 64.1%, respectively. The ratio 'nearest-neighbour distance/maximum intraspecific divergence' was lower than 1 for 26.1% of the samples, indicating possible taxonomic problems. In ten genera, belonging to six families, the number of species inferred from mtDNA data exceeded the number of species identified using morphological features; and in four cases indications of possible synonymy were detected. Finally, the DNA barcodes confirmed previously known identification problems within certain genera of the Clariidae, Cyprinidae and Mormyridae. Our results underscore the large number of taxonomic problems lingering in the taxonomy of the fish fauna of the Congo basin, and illustrate why DNA barcodes will contribute to future efforts to compile a reliable taxonomic inventory of the Congo basin fish fauna. Therefore, the obtained barcodes were deposited in the reference barcode library of the Barcode of Life Initiative. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Full-text · Article · Jul 2015 · Molecular Ecology Resources
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    ABSTRACT: The unparalleled biodiversity of Lake Tanganyika (Africa) has fascinated biologists for over a century; its unique cichlid communities are a preferred model for evolutionary research. Although species delineation is, in most cases, relatively straightforward, higher-order classifications were shown not to agree with monophyletic groups. Here, traditional morphological methods meet their limitations. A typical example are the tropheine cichlids currently belonging to Simochromis and Pseudosimochromis. The affiliations of these widespread and abundant cichlids are poorly understood. Molecular work suggested that genus and species boundaries should be revised. Moreover, previous morphological results indicated that intraspecific variation should be considered to delineate species in Lake Tanganyika cichlids. We review the genera Simochromis and Pseudosimochromis using an integrative approach. Besides a morphometric study and a barcoding approach, monogenean Cichlidogyrus (Platyhelminthes: Ancyrocephalidae) gill parasites, often highly species-specific, are used as complementary markers. Six new species are described. Cichlidogyrus raeymaekersi sp. nov., C. muterezii sp. nov. and C. banyankimbonai sp. nov. infect S. diagramma. Cichlidogyrus georgesmertensi sp. nov. was found on S. babaulti and S. pleurospilus, C. franswittei sp. nov. on both S. marginatus and P. curvifrons and C. frankwillemsi sp. nov. only on P. curvifrons. As relatedness between Cichlidogyrus species usually reflects relatedness between hosts, we considered Simochromis monotypic because the three Cichlidogyrus species found on S. diagramma belonged to a different morphotype than those found on the other Simochromis. The transfer of S. babaulti, S. marginatus, S. pleurospilus and S. margaretae to Pseudosimochromis was justified by the similarity of their Cichlidogyrus fauna and the intermediate morphology of S. margaretae. Finally parasite data also supported the synonymy between S. pleurospilus and S. babaulti, a species that contains a large amount of geographical morphological variation.
    Full-text · Article · Apr 2015 · PLoS ONE
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    ABSTRACT: The species flocks of cichlid fishes in the East African Great Lakes are the largest vertebrate adaptive radiations in the world and illustrious textbook examples of convergent evolution between independent species assemblages. Although recent studies suggest some degrees of genetic exchange between riverine taxa and the lake faunas, not a single cichlid species is known from Lakes Tanganyika, Malawi and Victoria that is derived from the radiation associated with another of these lakes. Here, we report the discovery of a haplochromine cichlid species in Lake Tanganyika, which belongs genetically to the species flock of haplochromines of the Lake Victoria region. The new species colonized Lake Tanganyika only recently, suggesting that faunal exchange across watersheds and, hence, between isolated ichthyofaunas, is more common than previously thought.
    Full-text · Article · Mar 2015 · Royal Society Open Science
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    ABSTRACT: The faunal diversity of Lake Tanganyika, with its fish species flocks and its importance as a cradle and reservoir of ancient fish lineages seeding other radiations, has generated a considerable scientific interest in the fields of evolution and biodiversity. The Tropheini, an endemic Tanganyikan cichlid tribe, fills a peculiar phylogenetic position, being closely related to the haplochromine radiations of Lakes Malawi and Victoria. Several problems remain regarding their genus-level classification. For example, the monotypic genus Interochromis is phylogenetically nested within Petrochromis; its only representative, I. loocki, has often been reclassified. As monogenean flatworms are useful markers for fish phylogeny and taxonomy, the monogenean fauna of Interochromis loocki was examined and compared to that of other tropheine cichlids. Three new monogenean species belonging to Cichlidogyrus are described from Interochromis loocki: Cichlidogyrus buescheri Pariselle and Vanhove, sp. nov., Cichlidogyrus schreyenbrichardorum Pariselle and Vanhove, sp. nov. and Cichlidogyrus vealli Pariselle and Vanhove, sp. nov. Their haptoral anchors remind more of congeners infecting species of Petrochromis than of all Cichli­dogyrus spp. hitherto described from other tropheine cichlids. Attachment organ morphology has been proven to mirror the phylogenetic affinities of Cichlidogyrus lineages. Therefore the monogenean parasite fauna of I. loocki reflects this host’s position within Petrochromis. Moreover, I. loocki differs in habitat choice from Petrochromis spp. This study hence confirms that host range and host-specificity in Cichlidogyrus spp. parasitizing tropheines is determined by the host’s phylogenetic position, rather than by a shared ecological niche.
    Full-text · Article · Jan 2015 · Contributions to zoology Bijdragen tot de dierkunde
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    ABSTRACT: 1. In semi-arid regions, the construction of small reservoirs is important in alleviating water shortage, although many have poor water quality with high turbidity and dense blooms of algae and cyanobacteria, and there are large differences in the ecology of such reservoirs. 2. We took advantage of two exceptionally dry years in northern Ethiopia to study the effect of a dry period and the associated fish kills on reservoir ecology and water quality. We studied 13 reservoirs, seven of which dried up in 2009. Four of the latter dried up again in 2010. We monitored the ecology of these reservoirs from 2009 to 2011, hypothesising that the pattern of reservoir drying would explain ecological differences among them. 3. Reservoirs that refilled after drying had a significantly lower fish biomass, lower biomass of phytoplankton (expressed as chlorophyll-a) and cyanobacteria (Microcystis), clearer water, greater macrophyte cover and lower nutrient concentrations than reservoirs that did not dry. Although the differences in water quality were most striking in the wet season after a drying event, there were persistent effects on reservoir ecology. The three categories of reservoirs we distinguished, based on their behaviour in 2009 and 2010, also showed differences in 2004, a year during which none of the reservoirs dried out. While drying evidently results in better water quality, we could not disentangle the effects of drying per se from that of reductions in fish biomass. The total combined effect was highly significant in all 3 years, whereas the separate effects of drying and loss of fish were only significant in 2004. 4. Our results suggest that differences in water quality and ecology among reservoirs depend on their propensity to dry out. Drying might be used as a restoration measure to reduce potentially harmful cyanobacterial blooms in reservoirs. Keywords: Ethiopia, fish biomass, Microcystis, reservoir ecology, water clarity
    Full-text · Conference Paper · Oct 2014
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    ABSTRACT: Riverine fish that colonize reservoirs can have a strong influence on the ecology of these systems. To understand this impact, it is important to know what they feed upon. In the reservoirs, they are exposed to different food sources compared to the riverine environment. We studied diet of 404 specimens belonging to two species of the riverine cyprinid genus Garra (G. blanfordii and G. dembecha) from six reservoirs in the highlands of northern Ethiopia using gut contents analysis. Detritus was an important food resource for both species. There was a significant difference in diet composition between G. blanfordii and G. dembecha. While detritus was the dominant food item in both, the diet of G. dembecha is distinguished from that of G. blanfordii by a lower detritus proportion, an additional dominance of chironomid food items. The diet composition of G. dembecha was similar in all reservoirs, whereas the diet composition of G. blanfordii varied among reservoirs and depended on prey availability. The benthic feeding habits of Garra in the reservoirs, reflected by high proportion of detritus and chironomids may contribute to sediment resuspension by disturbing the bottom sediment, and may thus affect reservoir ecology through nutrient enrichment.
    No preview · Conference Paper · Oct 2014
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    ABSTRACT: Labeo rosae, a species with a native range in Southern Africa, was discovered in the Congo basin by re-identification of two museum specimens previously identified as Labeo mesops. The occurrence of this species in the upper Congo implies a range extension of the species of more than 1000 km. Although the species' distribution is mirrored by that of some other Cypriniformes, its occurrence in the Congo might be due to introduction by humans.
    Full-text · Article · Aug 2014 · Journal of Fish Biology
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    ABSTRACT: A checklist of the fishes of the Upper Luapula area, situated in the Bangweulu-Mweru ecoregion (Upper Congo) between the Bangweulu swamps and the Mumbatuta falls, is presented, with details of the distribution and com- mon names in English and Bemba. Seventy-one species are recorded, 33 of which belong to the Cyprinidae and Cichlidae. Ichthyofaunal comparisons confirm the inclusion of the Upper Luapula area within the species-poor Bangweulu–Chambeshi subregion. This subregion was previously thought to have a Zambezian rather than a Congolese ichthyofauna. However, ichthyofaunal comparisons showed a higher similarity with the Congo basin. This study presents an updated list of the fishes of Kasanka National Park, the sole protected area within the Upper Luapula area. Five synomymies are presented and the recent introduction of an exotic species, Oreochromis andersonii, is reported.
    Full-text · Article · Apr 2014 · Ichthyological Exploration of Freshwaters
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    ABSTRACT: 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.
    No preview · Article · Mar 2014 · Journal of Natural History
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    ABSTRACT: In semi-arid regions, the construction of small reservoirs is important in alleviating water shortage, although many have poor water quality with high turbidity and dense blooms of algae and cyanobacteria, and there are large differences in the ecology of such reservoirs.We took advantage of two exceptionally dry years in northern Ethiopia to study the effect of a dry period and the associated fish kills on reservoir ecology and water quality. We studied 13 reservoirs, seven of which dried up in 2009. Four of the latter dried up again in 2010. We monitored the ecology of these reservoirs from 2009 to 2011, hypothesising that the pattern of reservoir drying would explain ecological differences among them.Reservoirs that refilled after drying had a significantly lower fish biomass, lower biomass of phytoplankton (expressed as chlorophyll-a) and cyanobacteria (Microcystis), clearer water, greater macrophyte cover and lower nutrient concentrations than reservoirs that did not dry. Although the differences in water quality were most striking in the wet season after a drying event, there were persistent effects on reservoir ecology. The three categories of reservoirs we distinguished, based on their behaviour in 2009 and 2010, also showed differences in 2004, a year during which none of the reservoirs dried out. While drying evidently results in better water quality, we could not disentangle the effects of drying per se from that of reductions in fish biomass. The total combined effect was highly significant in all 3 years, whereas the separate effects of drying and loss of fish were only significant in 2004.Our results suggest that differences in water quality and ecology among reservoirs depend on their propensity to dry out. Drying might be used as a restoration measure to reduce potentially harmful cyanobacterial blooms in reservoirs.
    Full-text · Article · Feb 2014 · Freshwater Biology
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    ABSTRACT: Intra-specific morphological variation in the cichlid Tropheus duboisi from 10 localities over its entire known distribution area along the central eastern and northern shore of Lake Tanganyika was investigated. This revealed significant differences between various populations that are geographically isolated. These morphological observations only partially correspond to the results of a haplotype network, based on mtDNA. In addition, a difference in the timing of the onset of the adult colour pattern was discovered for one isolated population. The occurrence of morphological intra-specific differentiation is discussed with respect to the basal position of T. duboisi within Tropheus as well as to the presumed morphological stasis of the genus.
    Full-text · Article · Nov 2013 · Hydrobiologia
  • E. Decru · J. Snoeks · E. Vreven
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    ABSTRACT: Re-examination of the holotype of Hepsetus odoe indicates that it falls within the range of H. akawo and consequently H. akawo is a junior synonym of H. odoe. As a result, the specimens from the western part of West Africa (from the Senegal to the Cavally River), formerly attributed to H. odoe, remain unnamed. The species is named as H. occidentalis, new species.
    No preview · Article · Nov 2013
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    Full-text · Conference Paper · Aug 2013
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    Full-text · Dataset · Jun 2013
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    ABSTRACT: Garra species are among the most abundant fish in small rivers of northern Ethiopia. Many manmade reservoirs in the region have been colonized by Garra, which often are the only fish species present and have become very abundant. Little is known about the ecology of these reservoir populations of riverine species. In this study we investigated the distribution patterns and gut fullness of 2 dominant species, G. blanfordii and G. geba, in 3 recently created reservoirs (Gereb Awso, Tsinkanet, and Mai Gassa I) in Tigray, northern Ethiopia. Species composition differed among reservoirs. Our data on fish catch densities and the fullness of the foregut suggest that the ecology of the Garra populations in the reservoirs is likely influenced by the avoidance of predation by birds. G. blanfordii, and to a lesser extent G. geba, foraged most actively after sunset.
    Full-text · Article · Apr 2013 · Inland Waters
  • E Decru · E Vreven · J Snoeks
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    ABSTRACT: 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.
    No preview · Article · Apr 2013 · Journal of Fish Biology

  • No preview · Article · Feb 2013 · European Journal of Taxonomy

Publication Stats

1k Citations
208.93 Total Impact Points

Institutions

  • 2003-2016
    • Royal Museum for Central Africa
      • • Department of Biology
      • • Department of African Zoology
      Tervueren, Flanders, Belgium
  • 2014
    • Mekelle University
      • Department of Chemistry
      Makalle, Tigray, Ethiopia
  • 1990-2013
    • University of Leuven
      • Department of Biology
      Louvain, Flemish, Belgium
  • 2006
    • Universität Konstanz
      • Department of Biology
      Constance, Baden-Württemberg, Germany
  • 2001
    • Cornell University
      Итак, New York, United States
  • 1997
    • The Catholic University of America
      Washington, Washington, D.C., United States