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Feeding ecology of the mangrove oyster, <i>Crassostrea gasar</i>(Dautzenberg, 1891) in traditional farming at the coastal zone of Benin, West Africa

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Natural Science 2013年第12期5卷 1238-1248页

作者： Alphonse Adite Stanislas P. Sonon Ghelus L. Gbedjissi Laboratoire de Parasitologie & Ecologie Parasitaire Département de Zoologie Faculté des Sciences et Techniques Université d’Abomey-Calavi Cotonou Bénin precob Unité de Recherches sur les Zones Humides (URZH) Département de Zoologie Faculté des Sciences et Techniques Université d’Abomey-Calavi Cotonou Bénin

Wild collection management and farming of the mangrove oyster (Crassostrea gasar) occurring widely at the Benin (West Africa) coastal zone require knowledge on the feeding ecology to explore energy sources and nutritional needs. Six hundred thirty (630) individuals of C. gasar have been sampled in the rearing site at the Benin coastal lagoon to investigate on the trophic ecology of this cultivated bivalve. The diet analysis revealed that C. gasar is a filter-feeder foraging mainly on phytoplankton (72.70%) and substrate particles (22.95%). This trophic specialization results from anatomical structure, mainly the presence of gills which facilitate the filtering of number of plankton taxa. Dominant phytoplanktons ingested comprised of Diatomophycea (33.52%), Chlorophycae (17.19%), Scenedesmacae (13.80%), Dictyosphaeriacae (3.79%), and Pleurococcacae (2.75%). Eight genuses of phytoplankton, Polycystis, Coelosphaerium, Protococcus, Botryoccocus, Crucigenia, Melosira, Cyclotella, and Gyrosigma dominated the diet of C. gasar with aggreated volumetric proportions reaching 69.06% of the diet. Higher occurrences were recorded mainly for Melosira occurring in 263 (41.75%) stomachs, substrate particles in 211 (33.49%), and Polycystis in 151 (23.97%). C. gasar exhibited a high niche breadths varying from 4.54 to 5.78, suggesting that this bivalve consumed a high variety of food items, thus exhibiting a degree of trophic plasticity. Diet overlaps (?jk) among different size classes were high and varied from 0.71 to 0.98, indicating an ontogenetic diet shift pattern in C. gasar. Probably, to adapt to the benthic-muddy environment and to increase survival, C. gasar has evolved a specialized feeding mechanism and strategy to retrieve only needed nutrients for growth and to reject awful and nondigestible foods. Also, at the oyster rearing grounds, there is an evidence of shift in the food web structure leading to an increase of the biological productivity at the coastal zone. The out

关键词： Conservation Crassostrea Diet Overlaps Farming Filter-Feeder Food Web Foraging Strategy Phytoplankton

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Diet breadth variation and trophic plasticity behavior of the African bonytongue <i>Heterotis niloticus</i>(Cuvier, 1829) in the SôRiver-Lake Hlan aquatic system (Benin, West Africa): Implications for species conservation and aquaculture development

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Natural Science 2013年第12期5卷 1219-1229页

作者： Alphonse Adite Adam Gbankoto Ibrahim Imorou Toko Emile Didier Fiogbe Département de Physiologie Animale Laboratoire de Pharmacologie Faculté des Sciences et Techniques Université d’Abomey- Calavi Cotonou Bénin Faculté d’Agronomie Université de Parakou (UNIPAR) Parakou Bénin precob Unité de Recherches sur les Zones Humides Département de Zoologie Faculté des Sciences et Techniques Université d’Abomey-Calavi Cotonou Bénin

The African bonytongue, Heterotis niloticus (Pisces: Osteoglossidae), is an omnivore foraging mainly on aquatic insects, microcrustacea, seeds and detritus. We examined the diet breadth and the trophic plasticity behavior of this species (1461 specimens) in the S? River and Lake Hlan water system located in the southern Benin (West Africa). Overall, the mean diet breadths of the two populations of Heterotis from both habitats were not significantly (p ≥ 0.05) different and were not associated with seasons. However, in Lake Hlan, mean diet breadths tended to increase with size (r = 0.81) and gut length (r = 0.82) indicating that bonytongues ingest a broader range of food resources as they grow. In both habitats, the positive correlation of both standard length (Log SL) and gut length (Log GL) with the volumetric proportions of detritus and with the volumetric proportions of seeds suggests that the consumption of these two food resources increased with the size of Heterotis and with the development of the digestive tract. Likewise, the negative correlation of both (Log SL) and (Log GL) with the volumetric proportions of aquatic insects and with the volumetric proportions of microcrustacea suggests that the consumption of these two food categories decreased as the size and the gut length of Heterotis increased. The differences in the consumption of microcrustacea (13.77% in Lake Hlan versus 2.63% in S? River) and mollusks (0.73% in Lake Hlan versus 4.91% in S? River) evidenced that Heterotis shifts his trophic structure according to resource availlability in the habitat. This foraging behavior suggests a degree of trophic plasticity in Heterotis. The specialized morphological structure of Heterotis, mainly the presence of a relatively high number of gill rakers (42 - 94 rakers on the first branchial arch) during its whole life, allowing sieving of zooplankton and other microcrustacea, and the presence of the gizzard favored this trophic plasticity. The broader diet bre

关键词： African Bonytongues Aquaculture Conservation Diet Breadth Foraging Behavior Gill Raker Omnivore Trophic Plasticity

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Fish Assemblages in the Degraded Mangrove Ecosystems of the Coastal Zone, Benin, West Africa: Implications for Ecosystem Restoration and Resources Conservation

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Journal of Environmental Protection 2013年第12期4卷 1461-1475页

作者： Alphonse Adite Ibrahim ImorouToko Adam Gbankoto Département de Physiologie Animale Laboratoire de Pharmacologie Faculté des Sciences et Techniques Université d’Abomey-Calavi Cotonou Bénin. Faculté d’Agronomie Université de Parakou (UNIPAR) Parakou Bénin precob Unité de Recherches sur les Zones Humides (URZH) Département de Zoologie Faculté des Sciences et Techniques Université d’Abomey-Calavi Cotonou Bénin

Mangrove forests are unique habitats in their function as potential food source and nurseries, and support an important fisheries resource. In the Benin coastal zone, the mangrove fishes have been surveyed to investigate fish species diversity, community structures and ecosystem degradation impacts in order to protect and to improve the mangrove fish resources. Results from wet, high-water and dry season samplings revealed that the two dominant mangrove species, Rizophora racemosa and Avicennia africana, are being intensively degraded for domestic use such as firewood and house building. Fifty one (51) fish species belonging to 25 families were recorded with Eleotridae (7 species), Cichlidae (5 species), and Mugilidae (5 species), the most speciose families. Dominant trophic guilds were detritivores (54.57%) and planktinovores/microcarnivores (30.41%). Six (6) species, Sarotherodon melanotheron, Dormitator lebretonis, Gerres melanopterus, Hemichromis fasciatus, Ethmalosa fimbriata, and Aplocheilichthys spilauchen, dominated the samples and accounted for about 80.27%. Sarotherodon melanotheron constituted the major dominant species and accounted numerically for about 29% of the total catches and 46.7% of the total biomass. The Margalef index of species richness ranged between 2.42 and 4.43, the Shannon-Weaver index of species diversity between 1.39 and 2.27, and the evenness between 0.50 and 0.62. Lower indices were observed for the highly degraded and the moderately degraded sites whereas higher indices were recorded for the less degraded and the restored sites. Species richness, species diversity and dominant species abundance were positively correlated with depth and transparency and negatively correlated with temperature. Multi-species fisheries dominate the coastal zone with Sarotherodon melanotheron, Dormitator lebretonis, Gerres melanopterus, Ethmalosa fimbriata, Liza falcipinus, Mugil sp. and Chrysichthys nigrodigitatus, the major species in the commercial ca

关键词： Conservation Detritivores Diversity Evolutionary Process Fragmentized Habitats Hydroelectrical Dam Mangrove Degradation Multi-Species Fisheries

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