Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Shallow genetic divergence and species delineations in the endemic Labeobarbus species flock of Lake Tana, Ethiopia
    Nagelkerke, L.A.J. ; Leon-Kloosterziel, K.M. ; Megens, H.J.W.C. ; Graaf, M. de; Diekmann, O.E. ; Sibbing, F.A. - \ 2015
    Journal of Fish Biology 87 (2015)5. - ISSN 0022-1112 - p. 1191 - 1208.
    To assess whether the species distinctions of Lake Tana’s Labeobarbus spp. are supported by genetic information, microsatellite markers were used. A total of 376 Labeobarbus spp., belonging to 24 populations of 11 species from three regions of the lake (north, south and east), were sampled. Eight microsatellite markers were analysed. In general, differences between conspecific populations were smaller than differences between populations of different species. For six species, conspecific populations from different regions in the lake were consistently more similar than populations of other species from the same region. For four species this was not the case, while for one species two populations were similar, but different from the third population. River-spawning species appeared to be more distinct than presumed lake spawners. On the species level, there was a significant correlation between genetic and morphological differentiation, especially in morphological aspects associated with ecological functioning. This suggests that genetic differentiation arose together with adaptive radiation, although the overall genetic differentiation among the Lake Tana Labeobarbus spp. is small.
    Effects of seed traits for the potential of seed dispersal by fish with contrasting modes of feeding
    Boedeltje, G. ; Spannings, T. ; Flik, G. ; Pollux, B.J.A. ; Sibbing, F.A. ; Verberk, W.C.E.P. - \ 2015
    Freshwater Biology 60 (2015)5. - ISSN 0046-5070 - p. 944 - 959.
    carp cyprinus-carpio - life-history traits - common carp - digestive-tract - ruppia-maritima - wetland plants - size - fruit - germination - floodplain
    For aquatic and riparian plants, the important role of fish in seed dispersal is increasingly recognised. While the propensity of seeds to disperse is known to be a function of morphological, physical and chemical traits of the seed, in the case of fish-mediated seed dispersal (ichthyochory), it is largely unknown how seed traits modulate the potential for seed ingestion and their subsequent survival through the gut. Furthermore, which seed traits are important may vary among fish species. To evaluate the role of both seed and fish traits in ichthyochory, we fed seeds of 19 aquatic and riparian plant species to fish with differing feeding mechanisms. Cyprinus carpio (common carp) has a pharyngeal ‘mill’, which it uses physically to crush hard food, while Oreochromis mossambicus (Mozambique tilapia) has only tiny oral and pharyngeal teeth and instead relies more on chemical digestion. A number of seed traits, including hardness, size and shape, were important determinants of the potential of seeds for ichthyochory. Certain traits (e.g. seed dimensions) were more important during ingestion, whereas other traits were more important for seed survival and subsequent germination (e.g. seed hardness, mucilaginous coat). Compared to controls, germination of retrieved seeds in carp was lower in 10 and higher in two plant species, whereas for tilapia, it was lower in seven and higher in three species. Overlap between these plant species was low, indicating clear difference between the fish studied in their potential for seed dispersal. Carp increased in size during the experiment and concomitant decreases in seed survival and retrieval were found, suggesting that body size and the correlated bite force is an important fish trait in ichthyochory. Overall, seed hardness, size and shape appear crucial for the survival of seeds passing through the guts of carp and tilapia. Beyond this general pattern, a greater complexity of trait-performance relationships appeared: different seed traits are involved during each of the stages of ichthyochory. Moreover, the importance of seed traits differed between carp and tilapia, with some traits having interactive and contrasting effects in both fish species. Aquatic plants with floating seeds adapted to hydrochorous dispersal were less likely to be dispersed by tilapia than plants with non-floating seeds, suggesting a dispersal trade-off between ichthyochory and hydrochory. Thus, depending on their seed characteristics, fish may offer an additional dispersal route to aquatic and riparian plants.
    Wat de vis eet, zal hij zaaien : Zaadverspreiding van water- en oeverplanten door vis
    Boedeltje, G. ; Spanings, T. ; Flik, G. ; Pollux, B.J.A. ; Sibbing, F.A. ; Verberk, W. - \ 2014
    Visionair : het vakblad van sportvisserij Nederland (2014)34. - ISSN 1569-7533 - p. 28 - 31.
    Het is essentieel voor planten om hun zaden te verspreiden over grote
    afstanden. Daarvoor maken ze gebruik van diverse vectoren zoals water,
    wind en dieren. Recent onderzoek laat zien dat ook vissen hierbij een
    belangrijke rol spelen.
    Eco-morphology as a predictor of fish diets in a changing North Sea
    Nagelkerke, L.A.J. ; Diderich, W.P. ; Sibbing, F.A. ; Rijnsdorp, A.D. - \ 2012
    In: Book of Abstracts of the 6th World Fisheries Congress, 07-11 May 2012, Edingburgh, Scotland. - - p. 7 - 11.
    We demonstrate the use of an eco-morphological method, quantifying the capacity of predatory fish species to utilize different prey types. Because this method focuses on the feeding capacity of predators and not only on their actual diets, this method potentially allows for the prediction of changes in food utilization in a changing environment and not only for detailed understanding of the actual interactions between predator and prey. To test the method we predicted the utilization of 31 different prey items in 9 species of gadoids and 12 species of flatfishes from the North Sea, through the following steps. 1) Categorisation of prey types in terms of physical (e.g. size, material properties) and chemical (e.g. carbohydrates / protein contents) properties that pose demands and selection pressure to their predators. This resulted in a functional, rather than in a taxonomic characterisation of prey types. 2) Identification of the required behaviour and morphological structures of the feeding, locomotory, and sensory apparatuses of predators to deal effectively with the demands of each food type. This resulted in a morphological profile for a specialist predator for each prey type. 3) Quantification of the same morphological structures in each fish species by detailed measurements, resulting in morphological profiles of each species. 4) Comparison of the specialist and species profiles. The extent to which the species profile fitted the specialist profiles resulted in a quantitative measure expressing the ability of each species to utilize a particular prey type: a hypothetical food niche (HFN). 5) Validation of the HFNs of all species by contrasting them with actual diets. We found that the gadoid and flatfish species could be separated in five “predatory groups”: large-mouthed flatfish, small-mouthed flatfish, soles, predatory gadoids and omnivorous gadoids. The utilization of fast, relatively large prey was predicted better than the utilization of slow or sessile prey that is well hidden, hard to crack or otherwise “tough to handle”. Overall predictions succeed in separating different feeding guilds, but in some cases do not succeed in distinguishing between species. Knowledge on feeding behaviour on slow and sedentary benthic prey is a limiting factor in this stage of methodology development.
    Spawning migrations of the endemic Labeobarbus (Cyprinidae, Teleostei) species of Lake Tana, Ethiopia: status and threats
    Anteneh, W. ; Getahun, A. ; Dejen, E. ; Sibbing, F.A. ; Nagelkerke, L.A.J. ; Graaf, M. de; Wudneh, T. ; Vijverberg, J. ; Palstra, A.P. - \ 2012
    Journal of Fish Biology 81 (2012)2. - ISSN 0022-1112 - p. 750 - 765.
    The reproductive biology of the only known intact species flock of large cyprinids, the 16 Labeobarbus species of Lake Tana (Ethiopia), has been extensively studied for the past two decades. Seven species of Labeobarbus are known to migrate >50 km upstream into tributary rivers for spawning during the rainy season (July to October), whereas eight other species are absent from these rivers and probably developed a new strategy of lacustrine spawning (macro-spatial segregation). One species (L. intermedius) probably spawns in the lake as well as in the rivers. Between the early 1990s and 2000s, the riverine spawners showed a decline of 75% in both biomass and number in both fishery independent surveys and in commercial catches. Reproductive migration makes fishes vulnerable to fisheries and other threats like habitat modifications. Lacustrine spawners are probably more resilient as they are not known to form spawning aggregations that can easily be exploited by fishermen. In addition, upstream rivers and catchments around Lake Tana are highly degraded by erosion and recently subjected to intensive habitat modification for irrigation and hydroelectric power generation. This article reviews results of field studies on the Labeobarbus spawning migration from Lake Tana to spawning rivers, giving emphasis on segregation and homing. It also summarizes existing and emerging threats which form potential causes for the decline of the migratory Labeobarbus species. Knowledge gaps on the reproductive biology are identified for further investigation
    Diversification of prey capture techniques among the piscivores in Lake Tana's (Ethiopia) Labeobarbus species flock (Cyprinidae)
    Graaf, M. de; Weerd, G.H. van de; Osse, J.W.M. ; Sibbing, F.A. - \ 2010
    African Zoology 45 (2010)1. - ISSN 1562-7020 - p. 32 - 40.
    buccal pressure - teleostei - pike
    Lake Tana harbours the only known intact species flock of large cyprinid fishes (15 Labeobarbus spp.). One of the most curious aspects of this species flock is the large number (8) of piscivorous species. Cyprinids are not well designed for piscivory (i.e. small slit-shaped pharyngeal cavity, lack of teeth in the oral jaws, lack of a stomach), which raises the question how well adapted these labeobarbs actually are to function as piscivores? In this study we analyse the kinematics of prey capture (by varied combinations of suction, swimming and jaw protrusion) among Lake Tana's piscivorous labeobarbs. Suction feeding kinematics were similar to values reported for other piscivorous fish species. A detailed analysis of several Labeobarbus species displayed distinct types of techniques (overswimming, velocity/volume suction with jaw protrusion) suited to capture elusive prey in different macro-habitats, Lake Tana's Labeobarbus species evolved a wide range of piscivorous predation techniques, a unique scenario for cyprinid fishes.
    Experimental evidence for the biological species status in Lake Tana’s Labeobarbus flock (Cyprinidae)
    Graaf, M. de; Nagelkerke, L.A.J. ; Palstra, A.P. ; Sibbing, F.A. - \ 2010
    Animal Biology 60 (2010)2. - ISSN 1570-7555 - p. 183 - 193.
    barbus-intermedius complex - reproductive segregation - ecological divergence - sympatric speciation - cichlid fishes - ethiopia - evolution - africa - origin - salmon
    Lake Tana (Ethiopia) harbours the only known remaining intact species flock of large (max. 100 cm standard length, SL) cyprinid fishes (15 Labeobarbus spp.). In 'common garden' experiments progeny of the riverine spawning benthivorous L. tsanensis, and of the piscivorous L. truttiformis and L. megastoma was raised under similar environmental conditions to test if interspecific morphological differentiation would occur. Interspecific morphological differences and divergence were clearly observed early in ontogeny (= 40 mm SL). This study is the first to demonstrate direct proof for the genetic basis of morphological differentiation among these labeobarbs, providing further support that Lake Tana's labeobarb species are true biological species
    Preliminary insight into the age and origin of the Labeobarbus fish species flock from Lake Tana (Ethiopia) using the mtDNA cytochrome b gene
    Graaf, M. de; Megens, H.J.W.C. ; Samallo, J. ; Sibbing, F.A. - \ 2010
    Molecular Phylogenetics and Evolution 54 (2010)2. - ISSN 1055-7903 - p. 336 - 343.
    late pleistocene desiccation - barbus-intermedius complex - cichlid fishes - molecular phylogeny - reproductive segregation - ecological divergence - dna-sequences - east-africa - cyprinidae - speciation
    The high diversity of Cyprinid fish in Ethiopia’s Lake Tana appears to be an example of ecological differentiation and assortative mating leading to rapid sympatric speciation. Lake Tana’s Labeobarbus species flock consists of 15 morphological and ecological distinct species. This is the first attempt to determine the age and origin and inter-species relationships of Lake Tana’s Labeobarbus species using the mtDNA cytochrome b gene. Analysis of cytchrome b sequences shows that Lake Tana’s species flock appears to be young but the present dataset did not unequivocally support monophyly of Lake Tana’s species. Additional markers are needed to determine whether Lake Tana’s labeobarbs originated from a single or multiple incursion(s) of ancestral L. intermedius in the Lake Tana drainage basin, or the disruption of an ancient continuous riverine population by the emergence of the Tissisat waterfalls. Adaptive radiation and speciation within Lake Tana’s Labeobarbus species flock may have occurred in the last 10,000–25,000 years, following the desiccation of Lake Tana around 17,000 years ago, at the same time as Lake Victoria, however, obtaining more data using other (nuclear) markers is urgently required
    Growth, biomass, and production of two small barbs (Barbus humilis and B. tanapelagius, Cyprinidae) and their role in the food web of Lake Tana (Ethiopia)
    Dejen, E. ; Vijverberg, J. ; Nagelkerke, L.A.J. ; Sibbing, F.A. - \ 2009
    Hydrobiologia 636 (2009)1. - ISSN 0018-8158 - p. 89 - 100.
    species flock - seasonal-variation - fish - zooplankton - model
    Growth, biomass and production of two small barbs (Barbus humilis and Barbus tanapelagius) and their role in the food web of Lake Tana were investigated. From length–frequency distribution of trawl monitoring surveys growth coefficient, F' values were estimated at 3.71–4.17 for B. humilis and 3.70–4.14 for B. tanapelagius, respectively. Values for B. humilis were confirmed in pond experiments. Mean biomass of the small barbs was 13.3 kg fresh wt ha-1, with B. humilis being most abundant in the littoral and sub-littoral zones, whereas B. tanapelagius was most abundant in the sub-littoral and pelagic zones. The two small barbs had a production of 53 kg fresh wt ha-1 year-1. Although their P/B ratios of about 4.0 were relatively high for small cyprinids, both their biomass and production were low in comparison with other small fish taxa in other tropical lakes. Of the zooplankton production only about 29% was consumed by the small barbs. However, they did not utilize calanoid copepods, which were responsible for approximately 57% of the zooplankton production and it is likely that small barb production was food limited during certain periods of the year. Piscivorous labeobarbs consumed about 56% of the small barbs production annually, but additionally, Clarias gariepinus, and many bird species were also preying on them. Therefore, limitation of Barbus production by predation during certain periods in the year cannot be excluded
    Lake Tana: Source of the Blue Nile
    Vijverberg, J. ; Sibbing, F.A. ; Dejen, E. - \ 2009
    In: The Nile. Origin, Environments, Limnology and Human Use / Dumont, H.J., Springer Science + Business Media B.V. (Monographiae Biologicae 89) - ISBN 9781402097256 - p. 163 - 192.
    Fisheries in the Nile System
    Witte, F. ; Graaf, M. de; Mkumbo, O.C. ; El-Moghraby, A.I. ; Sibbing, F.A. - \ 2009
    In: The Nile. Origin, Environments, Limnology and Human Use / Dumont, H.J., Springer Science + Business Media B.V. (Monographiae Biologicae 89) - ISBN 9781402097256 - p. 723 - 748.
    Fish Fauna of the Nile
    Witte, F. ; Oijen, M.J.P. van; Sibbing, F.A. - \ 2009
    In: The Nile. Origin, Environments, Limnology and Human Use / Dumont, H.J., Springer Science + Business Media B.V. (Monographiae Biologicae 89) - ISBN 9781402097256 - p. 647 - 676.
    Lake Tana's (Ethiopia) Labeobarbus Species Flock (Cypriniformes: Cyprinidae): a Future of Biodiversity Conservation and Sustainable Exploitation?
    Graaf, M. de; Nagelkerke, L.A.J. ; Dejen, E. ; Wudneh, T. ; Osse, J.W.M. ; Sibbing, F.A. - \ 2008
    In: Proceedings of the 4th International Conference on African Fish and Fisheries, Addis Ababa, Ethiopia, 22-26 September 2008. - Tervuren, belgium : Royal Museum for Central Africa - p. 31 - 47.
    Lake Tana, the source of the (Blue) Nile, is situated in the north-western highlands of Ethiopia and harbours an extraordinary diversity of cyprinid fishes. While cyprinid fishes are common and abundant throughout the world’s fresh water systems, the Labeobarbus species of Lake Tana form the only remaining intact species flock of large cyprinid fishes. Lake Tana and its Labeobarbus species flock provide(d?) an unique opportunity to study the selective forces driving speciation due, among others, to its relatively undamaged state. However, this undamaged state of the Labeobarbus species flock is seriously threatened by anthropogenic activities that have intensified over the past 30 years. Between the 1990s and early 2000s, Labeobarbus stocks decreased by 75%, most likely due to the increased fishing pressure after the introduction of a motorized commercial gillnet fishery. Many of the lake’s Labeobarbus species are highly vulnerable to exploitation during their spawning aggregations and upstream migrations. Erosion due to poor land use might have also contributed to habitat degradation of the upstream spawning sites. Between 2000 and 2010 the commercial fishing fleet has expanded from 5-10 to 50-100 boats, but the Labeobarbus CPUE of the commercial fishery appeared to have declined a further ~50% over the same period. A (final) blow to the survival of the species flock will probably be the planned and realized (Rib River) irrigation dams in the spawning rivers.
    Adaptive radiation of Lake Tana's Labeobarbus species flock (Pisces, Cyprinidae)
    Graaf, M. de; Dejen, E. ; Osse, J.W.M. ; Sibbing, F.A. - \ 2008
    In: Abstracts of the 4th International Conference of the Pan African Fish and Fisheries Association. - Addis Ababa, Ethiopia : - p. 43 - 43.
    Adaptive radiation of Labeobarbus species in Lake Tana
    Sibbing, F.A. ; Graaf, M. de; Dejen, E. ; Nagelkerke, L.A.J. ; Vijverberg, J. ; Osse, J.W.M. - \ 2008
    In: Abstracts of the 4th International Conference of the Pan African Fish and Fisheries Association. - Addis Ababa, Ethiopia : - p. 76 - 76.
    Shifts in taxonomic and trophic patterns of fish communities in African lakes in relation to (human-induced) pressures
    Nagelkerke, L.A.J. ; Sibbing, F.A. ; Zwieten, P.A.M. van; Graaf, M. de; Kolding, J. - \ 2008
    In: Abstracts of the 4th International Conference of the Pan African Fish and Fisheries Association. - Addis Ababa, Ethiopia : - p. 61 - 61.
    Geographical homogeneity of the Labeobarbus (Cyprinidae, Teleostei) species composition in Lake Tana, Ethiopia
    Nagelkerke, L.A.J. ; Oostenbrugge, J.A.E. van; Sibbing, F.A. - \ 2008
    In: Abstracts of the 4th International Conference of the Pan African Fish and Fisheries Association. - Addis Ababa, Ethiopia : - p. 60 - 60.
    Feeding performance and techniques of Lake Tana's eight piscivorous Labeobarbus spp (Pisces: Cyprinidae)
    Graaf, M. de; Weerd, G.H. van de; Sibbing, F.A. ; Osse, J.W.M. - \ 2008
    In: 4th International Conference of the Pan African Fish and Fisheries Association. - Addis Ababa, Ethiopia : - p. 114 - 114.
    Adaptive radiation of Lake Tana's (Ethiopia) Labeobarbus species flock (Pisces, Cyprinidae)
    Graaf, M. de; Dejen, E. ; Osse, J.W.M. ; Sibbing, F.A. - \ 2008
    Marine and Freshwater Research 59 (2008)5. - ISSN 1323-1650 - p. 391 - 407.
    late pleistocene desiccation - tropical fish assemblage - cichlid fishes - barbs barbus - east-africa - reproductive segregation - ecological divergence - victoria - speciation - origin
    Studying species flocks (e.g. Darwin¿s finches, Caribbean anoline lizards, East African cichlid fishes) has proven to be highly successful in understanding the forces driving speciation. The only known, intact species flock of cyprinid fishes, the 15 Labeobarbus species in Lake Tana (Ethiopia), includes eight piscivorous species. Piscivory is a rare specialisation among the highly successful (>2000 species) but mostly benthivorous Cyprinidae. The extent and mechanisms of diversification of this remarkable Labeobarbus species flock, particularly among the unexpected piscivorous species, are still largely unknown. In the present study we demonstrate that all 15 Labeobarbus species are segregated to a great extent along spatial, trophic and/or temporal dimensions. The spatial distribution, diet (prey species but not prey size), time of active feeding and predation techniques differed significantly among the eight piscivores. Lake Tana¿s cyprinids displayed their retained potential for ecological diversification and speciation, including the uncommon specialisation of piscivory. The latter is probably a result of the absence of common African specialist piscivores in Lake Tana. We suggest that the evolution of Lake Tana¿s Labeobarbus species flock at this stage is predominantly structured by ecological selection models. The labeobarbs most likely underwent sequential stages of radiation and speciation: habitat divergence followed by trophic divergence.
    Unexpected potentials for piscivory among the labeobarbs of Lake Tana (Ethiopia)
    Sibbing, F.A. ; Graaf, M. de - \ 2007
    In: Proceedings of the 12th European Congress of Ichthyology, Dubrovnik, Croatia, 9 - 13 September 2007. - Dubrovnik : - p. 172 - 172.
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