Effect of Dam on the Trophic Guilds Structure of Fish Assemblages in the Bia River-Lake Systems (South-Eastern Of Côte d'Ivoire)

This study compares fish trophic structure in the river-lake system Bia to Agneby river, a river with similar characteristics but have not impacted by the dam. Sampling sites were retained in upstream, the lake part and downstream areas of Bia river-lake system, and in upstream, middle stream and downstream of river Agneby. Samples were collected monthly during 23 surveys on each sampling zone with gillnets. A total of 78 and 45 fish species were recorded respectively in Bia and Agneby. Fish species were classified in nine trophic guilds using available information: Herbivore-microphage, Herbivore-phytoplanctonivore, Omnivore-benthophage, Omnivore-generalist, Omnivore-zooplanctonivore, Predator_1-insectivore, Predator_1-microphage, Predator_2generalist and Predator_2-piscivore. Predator_1-insectivore was most abundantly found in the rivers Bia and Agneby with respective percentage of 41.51 and 37.11. It is followed by Omnivore-generalist and Predator_2-generalist. Trophic guilds which are the most poorly represented are Herbivore-microphage (4.34%) and Predator_2-piscivore (3.97%) in Bia and Herbivore-microphage (0.62%) and Herbivore-phytoplanctonivore (2.89%) in Agneby. The analysis highlighted clearly two groups with no overlap in Bia river-lake system: samples from the lake and the upstream composed first group, and samples from the downstream are associated to second group. Two dominant guilds separating these two groups: Predator_2-generalist and Omnivore-generalist. The lake part and upstream are characterized by Omnivore-generalist, while Predator_2-generalist is mainly occurred in downstream. By contrast, samples from Agneby River couldn’t reveal any difference between downstream, middle part and upstream. The presence of dam on Bia main channel impact trophic guild structure of fish fauna by inhibiting communication between upstream and downstream.