Abstract. Pour résoudre les problèmes d'approvisionnement en eau potable des centres urbains, le gouvernement ivoirien a décidé d'utiliser les ressources pérennes telles que le fleuve Sassandra. Ainsi, le sous bassin du fleuve Sassandra en amont du barrage de Buyo est pressenti pour alimenter les villes de la région du Haut Sassandra et du département de Duekoué. Cependant, les intrants agricoles, les activités d'orpaillage et les déchets ménagers entrainent une forte contamination des eaux de ce fleuve en éléments traces métalliques (ETM). Ainsi, les tendances spatiales et temporelles de la pollution métallique ont été évaluées par le calcul des facteurs d'enrichissement, des indices de géo-accumulation, de l'indice de charge polluante, de l'indice de pollution sédimentaire et de l'indice de risque écologique individuel sur vingt-huit (28) échantillons provenant de sédiments de surface de ce fleuve. Les résultats montrent que des pollutions modérées à modérément sévères sont enregistrées au niveau du mercure (Hg) et du cuivre (Cu). Le Pb, l'As et le Cd connaissent un enrichissement modéré, avec des facteurs d'enrichissement respectifs de 1,77; 1,60 et 1,79 suggérant l'existence d'autres sources de métaux autres que la source naturelle terrigène. L'indice de pollution sédimentaire estimé à 5,95 (<10) montre que les sédiments sont moyennement pollués. Le risque écologique moyen lié aux Cd, As, Pb, Cu et Zn est largement inférieur à 40 traduisant un risque bas en référence à ces métaux avec le risque écologique moyen lié au Hg (160) largement supérieur à 40. L'analyse temporelle couplée au test SEQ-Eau montre également que le stockage des éléments traces métalliques au niveau des sédiments n'est pas définitif. Les risques de relargage, de remobilisation, de biodisponibilité et donc de toxicité, sont à craindre et constituent ainsi un danger permanent pour toute la chaîne trophique. Des mesures de prévention doivent donc être prises pour anticiper sur les difficultés que pourrait rencontrer le traitement de ces eaux pour les usages domestiques.

Pollution of aquatic ecosystems often results in adverse environmental disturbances, including individual and/or sub-individual changes in fish. The aim of the present study was to examine possible reproductive health effects in male and female, based on a histological assessment of Clarias gariepinus sampled in Bagoue River impacted by mercury from the artisanal gold mining. Fish were collected between August 2018 and April 2019 during two seasons from four stations differently impacted. A histological assessment was done on three target fish organs (liver, ovary and testis). Water and sediment samples were analysed for total mercury (T-Hg) concentration. Histological alterations were semi-quantitatively assessed, and the results were classified according to the severity of the histological response identified. Microscopic assessment revealed alterations of the gonads and liver tissues. A higher incidence of reaction pattern (Regressive changes, Inflammation and Circulatory disturbance) was found in liver tissues than in gonads tissues (Regressive changes). T-Hg levels were higher upstream than downstream in ovaries and testis tissues. Paradoxically, the lesions observed in these organs were more pronounced downstream than those found in fish from upstream during rainy season. According to total index, the organs examined downstream suffered severe damage unlike upstream sites. Also, comparison of degree of alteration between testes and ovaries indicates a greater impact of ovarian structures especially on downstream sites. The effect of anthropogenic impact appears to be visible downstream as the concentration of chemical pollutants and exposure time determine the severity of the damage. Alterations in ovarian follicles, spermatogenic cells and liver tissues may reflect damage to the process of gametogenesis, which may reduce the reproductive capacity of individuals over the long term.

Mormyrid fish Feeding habits Guinea Republic Dietary patterns of Brienomyrus brachyistius (Gill, 1862) in Tinguilinta and Kogon rivers were described. Diets composition and feeding strategy were analyzed among hydrosystems based on the stomach content analysis. The diets compositions were similar in the two rivers and essentially composed of insects larvae (Diptera, Coleoptera, Ephemeroptera and Trichoptera) and insects debris. Brienomyrus brachyistius exhibited a generalist feeding strategy with a relatively narrow niche width in the two rivers as there was a trophic specialization by many individuals toward Trichoptera larvae. Apart from insects, seeds and sand were found in many stomach contents. The ontogenetic analysis of diet indicated that there were not size-related changes in the diet of the studied species.

). The Z/K ratio (Z/K = 2.65 for S. mandibularis; Z/K = 4.85 for S. intermedius) indicated that mortality was predominant over growth for the two species. The recruitment pattern showed one Gauss curve translates was continuous for each species. For S. mandibularis, the exploitation rate (E = 0.47) was close to E 0.1 (E 0.1 = 0.46), indicating that S. mandibularis's stock was in an optimum state of exploitation. However, for S. intermedius, E max was lower (E max = 0.57) than the exploitation rate (E = 0.77). This result reflected overexploitation of this species.

1 ABSTRACT The phenotypic characterization of four populations of Oreochromis niloticus (Linnaeus, 1758) from the Haut-Sassandra region was carried out using 147 specimens. Among them, 39 were from the natural environment (Sassandra River) and 108 from three fish farms in the town of Daloa. The body weight, sixteen (16) metric characters and fifteen (15) meristic characters recorded on each individual made it possible to analyze the phenotypic variability of the four populations. Twenty-eight (28) on the 31 morphometric characters studied differentiated populations (P <0.001). Based on these 28 characters, Principal Correspondence Analysis (PCA) and Hierarchical Classification Analysis (HCA) grouped the individuals into two groups, a group consisting of Guessabo and PK 12(Kilometer 12 fish farm located at the end of the city of Daloa) specimens and the other group consisting of APDRACI and Quartier Manioc (two fish farms in the city) individuals. Six morphometric characters (PrAL. IOD. LDF. DAL. AFL and SsL) were the most relevant in the discrimination of these two groups. Discriminant factor analysis (DFA) has also classified these populations into two clusters identical to those of the PCA and the HCA. The brood stocks of PK 12 farm is morphologically identical to specimens of the natural environment (Guessabo). The waters of the PK 12 farm have similar characteristics to the natural environment. The PK 12 farm compared to the others (APDRACI and Quartier Manioc) would be better managed.