Twenty-two sites were monitored in the Lower Sassandra River Basin (Côte d'Ivoire, West Africa) to examine patterns in fish species assemblage structure along environmental gradients. Hierarchical clustering of the species presence-absence data identified four types of assemblages corresponding to the man-made Lake Buyo, the main channel, and the two major tributaries. Canonical Correspondence Analysis (CCA) indicated that canopy closure, leaves-wood, aquatic plants, temperature, width, total dissolved solids and depth were the environmental factors most strongly correlated with variation in the fish assemblages. Five species: Papyrocranus afer, Micralestes elongatus, Parailia pellucida, Tilapia busumana and T. mariae were reported from the basin for the first time. The investigation of the variation in species richness led to the assessment of a major anthropogenic disturbance induced by a palm oil factory. In conjunction with the fact that the Sassandra River hosts an endemic species, Synodontis koensis, it was concluded that this basin is of high conservation priority.

Objectives:The interest of this study is double. Firstly, these results allow for the characterisation of species assemblages, to identify their spatial distribution boundaries. Secondly, these findings are relevant to define spatial or ecosystem units in order to provide background for fisheries management. Methodology and Results: Samples were collected and studied at a grid of three zones during the cruise of investigation on board the Oceanographic Vessel ITAF DEME in March 2012. Forty-seven taxa belonging to four orders (Cephalopoda, Malacostraca, Chondrichtyes and Osteichtyes) were selected for analysis. Spatial differences in fish structure were analysed through different multivariate routines from PRIMER including between-matrix analysis of similarities (ANOSIM), species contributions to similarity/dissimilarity (SIMPER), non-metric multidimensional scaling (MDS) and group average cluster analysis. Typical or abundant species from those zones included fishes from the families Sparidae, Haemulidae, Carangidae. The most abundant species were Ariomma bondi (Ariommidae), Selene dorsalis (Carangidae), Brachydeuterus auritus and Pomadasys incisus (Haemulidae), Pagellus bellottii (Sparidae). The species Sardinella maderensis, Brachydeuterus auritus, Trachurus trecae and Selene dorsalis had the highest frequencies of occurrence. Conclusion and application: The distribution of the species halieutics is not uniform along the coast of Côte d'Ivoire. This study pointed to the fish resources of Côte d'Ivoire's Exclusive Economic Zone. These results will be used by the fishermen and for the development of adequate measures to prevent the loss of aquatic biodiversity.

Key-words:Synodontis koensis, endemic species, feeding habit, Sassandra River, Côte d'Ivoire In the implementation of programs for protection and management of ichthyofauna, endemic species should have high priority in the conservation measures. Their fishery should be based on intimate knowledge of their ecology and biology. Feeding habits of the endemic Mochokid Synodontis koensis were assessed in the Sassandra River (Côte d'Ivoire) in relation to the study zone, the specimen sex and size, and the season. Of the 303 stomachs examined, 49 were empty (16%). The fluctuation of the vacuity index indicated that S. koensis feeds more at night. The diet consisted mainly of plant detritus and chironomid larvae. The statistical analysis of the feeding according to the study zones, the sex of fish and the seasons does not show any significant difference between regimes, whereas significant ontogenic shifts in diet were observed. Dans la mise en oeuvre de programmes pour la protection et la gestion de l'ichtyofaune, les espèces endémiques doivent faire l'objet d'une attention particulière. Leur exploitation doit se faire sur la base d'une bonne connaissance de leurs éco-logie et biologie. Les habitudes alimentaires de Synodontis koensis, espèce endémique du fleuve Sassandra (Côte d'Ivoire), ont été étudiées pour la première fois en fonction de la zone d'étude, du sexe et de la taille des spécimens et de la saison. Sur 303 estomacs examinés, 49 étaient vides (16 %). La variation de l'indice de vacuité indique que S. koensis se nourrit surtout la nuit. Elle consomme principalement des débris végétaux et des larves de Chironomidae. Le régime alimentaire ne présente de variation statistiquement significative ni en fonction de la zone d'étude, du sexe et ni des saisons. À l'inverse, il est fonction de la taille des individus. RÉSUMÉ

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