Macroinvertebrates communities of a coastal lagoon in southern Benin, West Africa

The macroinvertebrate, assemblage investigated were collected in eight seasonal samplings from July 2007 through June 2009. A total of 4,179 individual macroinvertebrates were gathered, comprising 182 taxa belonging to 25 orders and 114 families. The most predominant groups were Molluscs and Crustacean which make up 71.11% of the taxonomic richness observed. Annelids and Insects were the second most predominant. This restricted biodiversity is based on a limited number of species such as Tympanotonus fuscatus radula, Pachymelania aurita, Neritina glabrata, Corbula sp., Clibanarius spp., Grandidierella africana, Nereis sp. and Chironomus sp.. Site typology based on environmental parameters reveals five assemblages in which no significant difference exists. The community is controlled by a salinity gradient but is also probably affected by hydrologic factors and human economic activities.Keywords: Macroinvertebrates, communities, distribution, abundance, diversity, lagoo

Le régime alimentaire de Schilbe multitaeniatus (Pellegrin, 1913) (Siluriforme, Schilbeidae) de la rivière Rembo Bongo au Gabon (Afrique Centrale)

S. multitaeniatus est un Schilbeidae tres capture et apprecie des eaux  douces du Gabon. Sa bioecologie peu etudiee a fait lfobjet dfune attention particuliere dans lfoptique de gerer durablement, de proteger et  entreprendre des essais de domestication en elevage de lfespece. De juin 2010 a decembre 2011, une etude experimentale de son regime  alimentaire a ete faite dans la riviere Rembo Bongo par lfanalyse de 292estomacs de poissons peches aux filets dormants de mailles 10, 15, 20, 25 30, 35, 40 et 50 mm. Les resultats ont montre que son alimentation est variee et constituee dfinsectes (Io = 36,5%; Iab= 29,29%), de poissons (Io= 24,31%; Iab = 18,18%), de debris dfanimaux (Io =  12,16%; Iab = 9,1%), de crustaces (Io = 4,06%; Iab = 5,05%), dfarachnides (Io = 1,35%; Iab = 1,01%), de fruits (Io = 13,51%; Iab = 28,28%) et de debris de vegetaux (Io = 6,76%; Iab = 6,06%). Cette alimentation differe entre jeunes-adultes (α = 0) dfune part et entresaisons de pluies et saison seche (α = -20) dfautre part. Globalement, lfespece a un regime omnivore a tendance ichtyophage, toutefois, avec une preference dfinsectes au stade jeune et de poissons au stade adulte.c 2013 International Formulae Group. All rights reserved.Mots cles : Cours dfeau, Siluriforme, Schilbe multitaeniatus, alimentatio

Ecological quality of the Alibori River, northern Benin, using macroinvertebrate indicators

The Alibori River, which flows through Benin’s cotton crop regions, receives surface water from much of the cultivated land that is situated along its banks. Chemical pollution in surface runoff from this land use threatens the ecological quality of the river. This study aimed to characterise the ecological status of the Alibori River under such agricultural pressures using biological indices and macroinvertebrate metrics. Water and macroinvertebrate samples were taken monthly from fifteen sites along the river between June 2015 and May 2016. The measured physico-chemical parameters and biological indices were subjected to descriptive statistics, bivariate correlations and partial least squares regression (PLSR). Taxonomic richness decreased from the upstream to the downstream reaches of the river. Sampling sites with high mineral content and organic load were home to more pollutiontolerant taxa, such as Chironomidae and Oligochaeta, with a high abundance of Thiaridae. Diversity indices reveal an unbalanced community and macroinvertebrate distribution characterised by the development of opportunistic taxa such as the gastropod Melanoides tuberculata. Decreases in taxonomic composition and community organisation between the upstream and downstream reaches of the river appear to be linked to less stable environmental conditions at the downstream sampling sites, and were compounded with a gradual increase in stress for organisms from the upper to lower reaches of the river. The composition, distribution and diversity characteristics of taxa collected is an indication that the ecological status of the Alibori River is under pressure, as a result of the agricultural activities along its banks

Paramètres de population et taux d'exploitation de Sarotherodon melanotheron melanotheron Rüppell (1852, Cichlidae) et Ethmalosa fimbriata Bowdich, 1825, Clupeidae) dans le lac Ahémé et ses chenaux avant le dragage (Bénin, Afrique de l'Ouest: Population parameters and exploitation rate of SarotherodonmelanotheronmelanotheronRüppell (1852, Cichlidae) and Ethmalosafimbriata (Bowdich, 1825, Clupeidae) in Lake Ahémé and its channels before dredging (Benin, West Africa)

Sarotherodon melanotheron melanotheron Rüppell (1852, Cichlidae) et Ethmalosa fimbriata (Bowdich, 1825, Clupeidae) figurent parmi les espèces de poisson les plus exploitées et les plus consommées par les populations riveraines du lac Ahémé et ses chenaux. En vue de réévaluer les paramètres de la population et le niveau d'exploitation de S. m. melanotheron et donner pour la première fois l'état des lieux pour E. fimbriata, la présente étude a été initiée. Les échantillons ont été collectés à partir des captures des pêcheurs d’octobre 2016 à septembre 2017. Les paramètres calculés sont : la relation poids-longueur, la taille de première maturité sexuelle, la mortalité par pêche, le taux d’exploitation, la taille de première capture, la longueur optimale et le recrutement saisonnier du poisson. Sur 1558 spécimens de Ethmalosa fimbriata analysés, la longueur totale a varié de 4,9 à 10,8 cm et le poids de 1,7 à 46,24 g, tandis que sur 2882 spécimens de S. m. melanotheron examinés, la longueur totale a varié de 5,8 à 18,4 cm et le poids total a varié de 3,4 à 109,77 g. Le coefficient d’allométrie b a été significativement différent de 3 pour les deux espèces et la croissance a été de type allométrie négative pour S. m. melanotheron et de type allométrie positive E. fimbriata. La taille de première maturité sexuelle a été estimée à 12,20 et 10,30 cm respectivement pour les mâles et les femelles de S. m. melanotheron et 8,3 et 7,5 cm respectivement pour les mâles et les femelles de E. fimbriata. La mortalité totale a été estimée à 2,56 et 2,89 an-1 respectivement pour S. m. melanotheron et E. fimbriata. Le recrutement est étendu sur toute l’année chez les deux espèces. Les caractéristiques environnementales, les paramètres physico-chimiques du milieu, la pression de pêche ainsi que le degré du parasitisme et toutes autres activités anthropiques sur le milieu sont autant de facteurs dont leurs variations ont influencé la croissance des espèces de poissons qui y vivent. Le stock de S. m. melanotheron dans le lac Ahémé et ses chenaux peut être supposé surexploité alors que celui de E. fimbriata reste non surexploité. Sarotherodon melanotheron melanotheron Rüppell (1852, Cichlidae) and Ethmalosa fimbriata (Bowdich, 1825, Clupeidae) are among the most exploited fish species and the most consumed by the riparian populations of Ahémé Lake and its channels. In order to reassess the population parameters the and the exploitation level of S. m. melanotheron and provide for the first time the status report for E. fimbriata, the present study has been initiated. The samples were collected from the catches of fishermen from October 2016 to September 2017. The parameters estimated were: the weight-length relationship, the size at first sexual maturity, the fishing mortality, the exploitation rate, the size catch, the optimal length and seasonal recruitment of fish. Out of 1558 specimens of Ethmalosa fimbriata analyzed, the total length varied from 4.9 to 10.8 cm and the weight from 1.7 to 46.24 g, while on 2882 specimens of S. m. melanotheron examined, the total length varied from 5.8 to 18.4 cm and the total weight varied from 3.4 to 109.77 g. The allometric coefficient b was significantly different from 3 for the two species and the growth was negative allometric for S. m. melanotheron and E. fimbriata positive allometric type. The size at first sexual maturity was estimated at 12.20 and 10.30 cm respectively for males and females of S. m. melanotheron and 8.3 and 7.5 cm respectively for males and females of E. fimbriata. Total mortality was estimated at 2.56 and 2.89 yr-1 respectively for S. m. melanotheron and E. fimbriata. Recruitment is spread throughout the year in both species. The environmental characteristics, the physicochemical parameters of the environment, the fishing pressure as well as the degree of parasitism and all other anthropogenic activities on the environment are all factors whose variations have influenced the growth of the fish species that live there. The stock of S. m. melanotheron in lake Ahémé and its channels may be assumed to be overexploited, while that of E. fimbriata remains unexploite