. Published online at www.m.elewa.org on 31 st July 2017 https://dx.doi.org/10.4314/jab/v115i1.7 RESUME Objectif : L'étude de diversité et la répartition des organismes zooplanctoniques du Lac Nokoué a été menée. Méthodologie et résultats : Pour la compréhension de cette composante importante de l'écosystème, un échantillonnage mensuel a été effectué sur 4 mois (juin à septembre 2015). Au cours de l'étude, 40 échantillons de zooplancton collectés au moyen d'un filet à plancton, dans 10 stations sont analysés. Au total, 31 taxa constitués de Copépodes, de Rotifères et de Cladocères ont été identifiés puis dénombrés. Les rotifères ont été le groupe le plus diversifié, avec une forte participation de la famille des Brachionidae. Sur le plan quantitatif, les nauplii de Copépodes ont été dominants à toutes les stations et en toutes périodes de l'étude. En général, une faible densité de zooplancton a été obtenue dans le lac. Toutefois, le mois de juillet et la station de Ganvié ont présenté des richesses taxinomiques et des densités élevées. Cependant les indices biologiques calculés ont indiqué une mauvaise répartition des individus dans la diversité zooplanctonique disponible. De plus, l'analyse de redondance réalisée entre les variables physico-chimiques et les principaux taxa a fait ressortir le taux de nitrate et celui d'ammonium comme les principaux paramètres qui déterminent les Copépodes et les Rotifères. Conclusion et application des résultats : Ces données bien que préliminaires ont montré que la distribution dans le lac du zooplancton est régie par la présence de matières organiques. Toutefois, une étude conduite sur une période plus ou moins longue combinant les facteurs physico-chimiques et la collecte du zooplancton contribuera davantage à la compréhension de la dynamique de cette communauté biologique du lac Mots clés : Zooplancton, diversité, densité, distribution, Canoco, lac Nokoué.ABSTRACT Objective: The study of the diversity and the distribution of zooplanktonic organisms of Nokoué Lake was conducted. Methodology and Results: For an understanding of this important component of the ecosystem, monthly sampling was carried out for four months June to September 2015). During the study, 40 zooplankton samples collected by plankton net, in 10 stations are analyzed. A total of 31 taxa consisting of Copepods, Rotifers and Cladocerans were identified and counted. Rotifers are the most diverse group, with strong participation of Brachionidae family. Quantitatively, Copepod nauplii were dominant at all stations and in all periods of the study. In general, a low density of zooplankton was obtained in the lake. However, July month and Ganvié station have registered high taxonomic richness and densities than other months and stations sampled. 11477However, the calculated biological indices indicate a distribution of individuals in the zooplankton diversity. In addition, the redundancy analysis carried out between the physico-chemical variables and key taxa highlighted the nitrate levels and ammonium levels, su...

Water hyacinth is a plant from America which was imported in Africa as an ornamental plant but because of its proliferation, has become a dangerous aquatic macrophyte. In Benin, it colonizes most courses in continental water. Water hyacinth is present in several areas of the world as an ornamental plant and its infestation can be controlled by several treatments. The objective of this work is to identify them and promote their valuation in order to reduce their dangerousness to the population of aquatic organism as well as their ecosystem. In this regard, a survey was carried out to overcome these problems the people of the town in Sô-Ava and around face every year on the Sô River flows into Lake Nokoue. The coverage of the water hyacinth (Eichhornia crassipes) is a major problem for people living in those areas where the plants rage. This plant prevents the movement of motorized boats, prevents the penetration of oxygen in water, which greatly reduces the number of organism such as fish fry, crocodiles nest and boas.

This work evaluates the growth and body development of Oreochromis niloticus in floating cages in the Toho Lake of Benin. Thus, 6000 juvenile monosex male with an average initial weight of 8.87 ± 4.89 g and average initial total length of 7.87 ± 1.43 cm were randomly distributed in two floating cages (5 x 5 x 2.5 m3) at the stocking density of 3000 fish/cage. The fish were hand-fed to apparent satiation, three times daily, using 45-32% crude protein commercial pelleted floating feed Skretting®. The physico-chemical parameters of lake water recorded every 72 hours during the experiment were within the suitable ranges for fish culture and were as follows: temperature (27.78 ± 0.41 °C), pH (7.55 ± 0.22), dissolved oxygen (4.03 ± 0.96 mg/l), ammonium (0.31 ± 0.18 mg/l), nitrite (0.29 ± 0.07 mg/l) and nitrate (0.27 ± 0.12 mg/l). The variables studied at the end of  the 215 days of rearing were as follows: final mean total length (26.61 ± 2.99 cm), final mean standard length (22.40 ± 2.74 cm), final mean predorsal length (6.93 ± 0.94 cm), final mean head length (3.45 ± 0.58 cm), final mean dorsal fin base length (13.55 ± 2.96 cm), final mean inter-orbital width (2.97 ± 0.37 cm), final mean body height (8.57 ± 1.56 cm) and final mean caudal peduncle height (3.27 ± 0.39 cm). The zootechnical growth parameters evaluated were as follows: survival rate (91.5%), final mean body weight (402.18 ± 137.05 g), average daily weight gain (1.83 ± 0.08 g), specific growth rate (0.77 ± 0.03%/day), feed conversion ratio (1.74 ± 0.09%) and protein efficiency ratio (1.62 ± 0.06). These results compared to the literature indicate interesting growth and body development and it would be important to promote in-cage farming of Oreochromis niloticus.