Fish diversity and assemblages according to distance from source along a coastal river gradient (Ehania River south-east of Ivory Coast)

Fish assemblage was investigated during the study of longitudinal profile of the Ehania River Basin in south-eastern Côte d’Ivoire. This area is subjected to intense human activities with many plantations (palm tree, banana, pineapple, coffee, rubber and cocoa). Samples were collected, with gillnets of different mesh sizes, through 6 sampling surveys during dry and rainy seasons from February 2010 to December 2010 at 6 sampling sites. A total of 70 fish species belonging to 48 genera, 28 families and 10 orders were recorded. The temporal variation of diversity index is less marked than spatial variation. The upstream, with 35 species, was less rich in species than the medium area and downstream areas (respectively 46 and 68). The upstream and downstream areas gathered 35 species. Thirty three species were common to the upper and middle areas and 46 species appeared both in the lower courses and the middle area. The 21 species restricted to the lower part of the river are mainly estuarine/marine origin. The beta diversity value revealed low similarity between the lower and upper course of Ehania River. The lowest values of Shannon’s diversity index and equitability index were observed in the middle part of the River which characterized by high population density and intense agricultural activity with many plantations

Relationships between morphometric characteristics of brackishwater prawn, Macrobrachium macrobrachion (Herklots, 1851), of Côte d’Ivoire (West Africa)

The present study describes the length-weight relationship (LWR), length-length relationship (LLR) and condition factor of the wild population of the shrimp Macrobrachium macrobrachion from the rivers of Côte d’Ivoire (West Africa). Samples were randomly collected from small-scale shrimp fisheries using bamboo traps. Of the thirteen analyzed morphometrics characters, only the second pleura width significantly varies between males (13.11 mm) and females (14.78 mm). All relationships between the considered variables were significantly linear, r^2 ranging from 0.66 to 0.97. For length-length relationships, the allometry coefficient varied depending on groups, environments and characters, and ranged between 0.64 and 1.26. The three allometry types (negative allometry, isometry and positive allometry) were observed in this relation. In length-weight relationship, the coefficient ranged from 2.02 to 2.78, indicating a negative allometry. The condition factor values showed that females (0.70±0.06) were in better condition than males (0.657±0.07). Overall, the condition factor followed an east-west gradient, decreasing from eastern (0.70) to western (0.63) regions. These results constituted an important biological database on M. macrobrachion from the rivers of Côte d’Ivoire for further studies as ecology, reproductive biology, and aquaculture potentialities of this species

Ecology and diversity of freshwater shrimps in Banco National Park, Côte d’Ivoire (Banco River Basin)

Shrimps are an important component of river invertebrate assemblages in tropical freshwater where they are a controlling group in food webs. In order to determine shrimp diversity in the Banco Basin (Côte d’Ivoire, West Africa) and examine whether the patterns of species distribution were related to environmental conditions, six sites were monitored. Sampling was conducted in 2008 during February, May, September and November using a long-handled net (25-cm diameter, 2-mm mesh). For each site, we measured environmental variables (conductivity, pH, water temperature, dissolved oxygen, turbidity, current speed, and water depth and width). Three shrimp species, Macrobrachium thysi (Powell 1980), Macrobrachium dux (Lenz 1910) and Desmocaris trispinosa (Aurivillius 1898) were identified. D. trispinosa was the largest distributed (more than 50% of occurrence) and the most abundant (67% of total number of specimens caught). It was followed by M. thysi with 47% and 32% of occurrence and abundance, respectively. Canonical correspondence analysis (CCA) showed a spatial distribution of the shrimp community, significantly influenced by width, depth, conductivity, type of substrate, turbidity and dissolved oxygen. Due to the fact that the Banco River hosts an endemic species in Côte d’Ivoire (Macrobrachium thysi), the conservation of integrity of this basin was recommended

Composition et variation spatio-saisonnière du peuplement algal des rivières côtières du Sud-est de la Côte d’Ivoire

Objectif : La composition et la distribution spatio-temporelle des micro-algues de quatre rivières du Sud-est de la Côte d’Ivoire (Soumié, Eholié, Ehania et Noé) ont été analysées, en relation avec des paramètres physicochimiques du milieu.Méthodologie et résultats : La zone pélagique et les supports littoraux (pierres, feuilles et bois) ont été échantillonnés en amont et en aval de chaque rivière. Au total, 192 taxons spécifiques et infraspécifiques ont pu être identifiés, parmi lesquels environ 75 % d’espèces de Diatomées, 10,4 % de Cyanobactéries, 9,9 % de Chlorophytes, 4,2 % d’Euglénophycées et 0,5 % de Rhodophycées. Les Diatomées constituent la classe la plus constamment rencontrées dans les prélèvements des quatre cours d’eau De plus les algues périphytiques sont plus diversifiées que celles de pleine eau. Les espèces Gyrosigma acuminatum, Nitzschia palea, Ulnaria biceps et Gomphonema parvulum sont communes à tous les habitats explorés.Conclusion : Les variations de la composition des peuplements entre les rivières sont relativement faibles, avec des diversités plus importantes dans la rivière Noé (134 taxons) et peu élevées dans la rivière Ehania (127 taxons). En outre, les algues récoltées sur feuille et sur bois présentent une forte similarité dans tous les cours d’eau prospectées.Mots clés : Phytoplancton, périphyton, diversité taxonomique, Rivières côtières, Côte d’Ivoire

Genetic identification of hybrids between two autochthonous tilapia species, Tilapia zillii and Tilapia guineensis, in the man-made lake Ayame

Tilapia species are able to hybridize in captivity or in natural conditions following introduction of alien species. Here, we report a case of hybridization between two (and perhaps three) autochthonous species, Tilapia zillii and T. guineensis, resulting from a modification of their environment due to human activities. The man-made dam Ayame (Cote d'Ivoire) transformed the River Bia into a lake (Lake Ayame, area: 197 km(2)). In this new environment, both tilapia species have hybridized. In order to study hybridization along the Bia System, 25 allozyme loci have been screened in 470 specimens from ten locations. Two loci LDH-1 and PGI-2 were diagnostic between the two different species and can be used to identify hybrids in each sampling location of the River Bia basin. The percentage of pure T. zillii individuals in Lake Ayame varied from 18.1% in Ebikro to 4.2% in Ketesso while percentage of pure T. guineensis varied from 81.3% in Yaou to 50.0% in Ebikro. The proportions of hybrids varied from 8.3% in Yaou to 31.9% in Ebikro. The existence of private alleles observed in tilapia from Lake Ayame compared to what has been observed in both reference populations, T. zillii and T. guineensis led to the hypothesis that a third species could have been engaged in this hybridization. This third species is likely to be T. busumana, formerly present in the lake but now rarely observed. If this natural hybridization is due to the dam construction and the correlated ecological changes, then other hybridizations could result since many dams have been constructed within the range of these species in Cote d'Ivoire

Genetics and aquaculture in Africa

Cette étude est une revue synthétique de l'aquaculture et de la biodiversité des tilapias à travers le monde mais surtout en Afrique, leur continent d'origine. Une présentation sommaire des #Cichlidae est donnée. Il en a été de même pour les trois genres de tilapia concernés par la pisciculture : #Tilapia s.s., #Sarotherodon et #Oreochromis. Une espèce du dernier genre cité, #O. niloticus$, apparaît de toute évidence comme l'espèce la plus polymorphe et la plus utilisée actuellement en pisciculture. Il se dégage également que les espèces à large distribution naturelle sont les plus impliquées dans les diverses activités de pisciculture. (Résumé d'auteur

Genetics and aquaculture in Africa

La vitesse de croissance de trois souches sauvages de #Oreochromis niloticus$, Ghana (GHA), Niger (NIG) et Sénégal (SEN), a été comparée à celle d'une souche domestique, la souche Bouaké (BKE). Cette souche provient d'un croisement entre une souche du bassin de la Volta (Burkina-Faso, arrivée en 1957) et une souche du bassin du Nil (Ouganda, arrivée en 1968). L'ensemble du matériel biologique était constitué de juvéniles, qui ont été grossis puis mis en reproduciton en bacs cimentés pour les comparaisons de croissance. Les différents tests se sont déroulés sur une période de cinq mois. La ration alimentaire, identique pour tous les étangs était basée sur le groupe ayant le poids moyen le plus élevé. Chaque mois, une pêche de contrôle a permis d'ajuster cette ration. Tous les poissons ont été pesés individuellement à la mise en charge et à la vidange. Sur le plan zootechnique, en nous basant sur l'évolution des poids moyens, la croissance journalière individuelle et l'indice de consommation, les souches présentant les meilleurs performances de croissance seraient BKE et SEN. Les conséquences sur l'utilisation de ces différentes souches sont discutées. (Résumé d'auteur

Disponibilité en poissons et pouvoir d'achat de la population dans la région du moyen Comoé (Côte-d'lvoire)

Fish Availability and Buying-power of the Local Population in the Central Comoe Region (Ivory Coast). The origin of commercial fish found on local markets in the "Moyen Comoe" area is diverse : imported frozen fish, fish coming from Abidjan and smoked in Akoupe (South Ivory Coast), locally caught fish and fish caught in neighbouring countries (Ghana and Mali). The atlantic horse mackerel and the round sardinella (frozen fish) are the most important commercial fish species found on the markets. These fish, sold at 350 francs CFA, can be afforded by the majority of the households, 82 % of which spend less than 1000 francs CFA for buying fish and/or meat (beaf)

Études préliminaires de la distribution spatio-temporelle du phytoplancton dans un système fluvio-lacustre africain (Bassin Bia ; Côte d'lvoire)

Les échantillons examinés mensuellement de novembre 1996 à octobre 1997 proviennent de divers endroits du système fluvio-lacustre de la Bia : deux sites dans le lac (Bakro et Ayamé) et deux dans le système fluvial dont un en amont (Bianouan) et un en aval (Aboisso). La structure et la dynamique du phytoplancton ont été appréciées. En amont du barrage, le peuplement est marqué, presque toute l'année, par une relative abondance des Diatomées Aulacoseira granulata et Fragilaria virescens. Dans le lac, l'évolution du peuplement phytoplanctonique est plutôt fonction des deux grandes saisons de I'année. Les Diatomées, principalement, Asterionella formosa, Aulacoseira granulata et A. granulata var. angustissima dominent le peuplement en saison sèche. Pendant les périodes pluvieuses de I'année, les Cyanophycées Microcystis aeruginosa, Anabaena spiroides constituent la composante majoritaire du phytoplancton dans les échantillons. En aval du barrage hydroélectrique, la dynamique du phytoplancton observée est plus ou moins semblable à celle ci-dessus décrite dans le système lacustre. Les variations des paramètres physico-chimiques enregistrées dans les différentes stations semblent peu influencer la densité du phytoplancton. Elle apparaît plutôt déterminée par le régime hydrologique de la rivière

Domestic wastewater treatment with a vertical completely drained pilot scale constructed wetland planted with Amaranthus hybridus

A pilot scale constructed wetland planted with Amaranthus hybridus was developed for domestic wastewater treatment. The reactor system was composed of rectangular beds realized in cement. Eachbed was filled from the bottom to the top with 0.1 m of gravel (15/25 mm) and 0.30 m of a white sand originating from the Ebrié lagoon. Two beds planted with yang A. hybridus plants (high density: 40plants/m²; low density: 10 plants/m²) and one control (unplanted bed) were used to perform the experiment. The pH of the overall filtrates decreased from 7 to around 8. Planted beds gave best CODremoval (high density = 70%, low density = 66%) than the control (60%). Globally nutrients were best removed in the planted beds (NH4+: 69%, PO4 3-: 67%) than in the control (NH4+: 15%; PO4 3-: 56%). However the important oxidation of NH4+ to NO2 - and NO3 - provoked their accumulation in these bedsfiltrates than in the control. The increase of the plant density seems to have any statistical significant impact upon pollutants removal between the two planted beds experimented. But augmenting plantdensity allows increasing the beds removal capacities. Plants leaves were less contaminated at 0.5 m height, suggesting it for their harvesting