Brachionus falcatus and Platyias patulus indicating organic pollution in Ouémé River’s basin, Republic of Benin

Zooplankton is a biological compartment widely used in the bio-monitoring of aquatic ecosystems. It allows early detection of environmental disturbances even before reaching the upper compartments of interest to humans. The present study evaluated the ability of two rotifer species Brachionus falcatus and Platyias patulus to indicate organic pollution in the Ouémé River basin. Sampling was done between October 2014 and September 2015. Plankton net of 20 μm mesh size was used. Parameters such as NH4+, NO2- and PO43- were measured in water and used for the calculation of the Organic Pollution Index (IPO). The results showed that the occurrence of B. falcatus and P. patulus was 96.66% and 81.11%, respectively. Both species were particularly abundant in sites such as Kaboua and Vossa as well as downstream of the basin (Agonlin-lowé and Bonou). These strong abundances are linked to a very strong organic pollution in Kaboua and Vossa then to a high organic pollution at downstream. The least organically polluted station (Kpassa) had the lowest abundance of both species. B. falcatus and P. patulus are therefore two indicator species of organic pollution in the Ouémé River’s basin in Benin

Composition and structure of phytoplankton community in Ouémé River basin, Republic of Benin

This study aimed to assess the composition and structure of floating phytoplankton assemblage in Ouémé basin. Phytoplankton samples were collected monthly from October 2014 to September 2015. Quantitative samples were taken with a horizontal Van-Dorn sampler and 20 μm mesh plankton net was used for additional qualitative sampling. Microscopic observation of phytoplankton allowed identification of 208 species including 70 Bacillariophyta species, 58 Chlorophyta species, 24 Charophyta species, 21 Euglenophyta species, 18 Cyanophytes species, 9 Phyrrophyta species, 5 Ochrophyta species and 3 Cryptophyta species. The Shannon diversity index varied from 2.4 bit.ind-1 and 3.1 bit.ind-1 showing a relatively good diversification of the community. The population appears largely dominated by 14 species which represent 83.8% of the total phytoplankton. Aulacoseira granulata and Euglena gracilis were the most predominant species with respectively 40.17% and 15.91% relative abundance. Regarding the horizontal pattern of phytoplankton abundance, downstream stations have the greatest abundances. So, the results suggest that downstream stations are richer in phytoplankton which structure differs from that in upper stations.

Composition and seasonal variation of phytoplankton community in Lake Hlan, Republic of Bénin

Knowledge of biodiversity of aquatic ecosystems is nowadays a challenge for global research. Phytoplankton being very important in the sustainability of ecosystems, its mastery allows the development of early monitoring and evaluation tools of the health status of aquatic environments. The study aims to make an initial inventory of phytoplankton of the lake Hlan and to evaluate the influence of hydrologic season on its dynamics. Plankton samples were collected monthly between May and December 2012 using plankton net of 30 µm size. They were then treated and species identified using light microscopy. 39 species in 7 classes (Bacillariophyceae, 18 species in 10 genera), (Cyanophyceae, 5 species in 5 genera), (Chlorophyceae, 5 species in 3 genera), (Zygnematophyceae, 3 species in 2 genera), (Trebouxiophyceae, 2 species in 2 genera) (Euglenophyceae, 4 species in 3 genera) and (Dinophyceae, 2 species in 2 genera) have been identified. The Shannon index varied between 4.8 and 5.1 bit cell-1. This shows that the ecosystem is balanced. Nevertheless, the presence of potentially toxic species requires a monitoring program for Lake Hlan

Identification of characteristic zooplankton species in the Kinyankonge River basin, Burundi

The objective of this study is to determine the zooplankton species that characterize the Kinyankonge River basin in Burundi. Thus, zooplankton was sampled monthly over a period of 18 months (from July 2015 to June 2016, then from January 2017 to June 2017) at seven stations. The Indicator Value (IndVal) of the identified zooplankton species and the coverage of stations were determined. The results showed that three species characterized significantly the most upstream station whereas the water of the irrigation channel was characterized by 4 species. The waters of the Nyabagere tributary and the wastewater treatment plant are characterized by 1 and 5 species, respectively. Furthermore, the dry season was characterized by 4 singletons and 13 pairs of species, while the rainy season was characterized by 11 pairs of species. Moreover, the group of upstream stations was characterized by 5 species while 3 species characterized the group of downstream stations. These species highlighted by the indicator value method can be used to characterize stations in the Kinyankonge River and provide information on seasonal changes

Reproduction and embryonic development in the African freshwater prawn Macrobrachium macrobrachion (Herklots, 1851)

The current study aimed to determine parameters and conditions for successful reproduction of Macrobrachium macrobrachion (Herklots, 1851) in a controlled medium and describing its embryonic development. A total of 122 adult specimens were collected from the delta of Ouémé River and stored in polyethylene tanks with 1:2 male-female sex ratio. This broodstock was fed on pelleted food (Biomar Efico) once a day. For the embryogeny monitoring, eggs were sampled each hour through the first two days after spawning and then every 2 hours till hatching. Spawning happened at a mean temperature, dissolved oxygen concentration and pH of 27.80±0.56°C, 5.83±0.45 mg/L and 7.41±0.34, respectively. The eggs incubation meantime was 12±1 days with nine main embryonic development stages. Hatching lasted on the average 21.00±1.94 h and led to larvae with a mean size of 2.30±0.90 mm. Mean fecundity was 13062.4±5489.93 eggs and 14715.2±6108 eggs, respectively for the first and second seasons with a highly significant difference between them. The best hatching rates were obtained with salinities equal to 2 and 4‰. The results constitute the first database for larval breeding of M. macrobrachion species

Exploitation Patterns of Anchovies (Engraulis encrasicolus) by Marine Artisanal Fisheries in Togo (West Africa)

Pelagic fish, including sardines and anchovies (Order Clupeiformes), are the most common species taken by artisanal marine fisheries along the Togolese coast. We investigated fisher involvement as well as fish captures over a period of 10 years, particularly of the European anchovy (Engraulis encrasicolus). Our results indicate that 60% of fishers operated from the Lomé fishing harbour, most fishers being Ghanaians working seasonally in Togo. 63.7% of all the fishers used canoes with outboards, a higher percentage compared to the previous decades. Seven fishing gear type were identified, with bottom gillnet and surface gillnet being the most commonly used. However, in the most important fishing camp in the country in terms of fish production (Lomé fishing harbour), all fishers used shark nets. Overall, fisheries catches did not change significantly across years, but anchovy fishing effort and catch per unit of effort (CPUE) declined over the study period, suggesting some depletion of the species stocks on the Togolese coast and a demotivation of fishers.

Fish farming in the existing water bodies: Techniques and species of interest in Benin

Pour la pisciculture dans les étendues d’eau existantes, la présente synthèse bibliographique montre que les cages et les enclos, deux infrastructures différentes dans leur conception et existant en plusieurs types, sont les infrastructures utilisées dans plusieurs pays tels que la Côte d’Ivoire, le Ghana, le Niger, le Nigeria et le Bénin. Aussi, plusieurs espèces notamment les tilapias (Oreochromis niloticus, Sarotherodon melanotheron et Coptodon guineensis) et les poissons-chats (Clarias gariepinus, Heterobranchus longifilis, Chrysichthys nigrodigitatus et Chrysichthys walkeri) y sont élevées. Au Bénin, O. niloticus et C. gariepinus, dont les caractéristiques biologiques et écologiques de pisciculture sont bien maîtrisées, constituent les deux principales espèces rencontrées dans les élevages. La quasi-totalité de la production en cages et en enclos du Bénin provient du département de l’Atlantique à travers le lac Toho-Todougba, qui héberge des installations privées à forte capacité de production de poisson contribuant à augmenter l’apport de l’aquaculture dans la production halieutique du pays. La valorisation des autres ressources aquatiques disponibles, à l’instar des nombreuses retenues d’eau pour la pisciculture en cages et enclos permettra au Bénin d'accroître sa capacité à nourrir la population. Toutefois, les inconvénients et impacts associés à ces pratiques doivent être suivis de prêt.Mots clés: Cages, enclos, poissons, eaux continentales existantesThe present review shows that cages and pens, two aquaculture systems different in their conception and of several types, are the infrastructures used in several countries such as Côte d’Ivoire, Ghana, Niger, Nigeria and Benin for fish farming in the existing water bodies. Fish species including tilapias (Oreochromis niloticus, Sarotherodon melanotheron and Coptodon guineensis) and catfishes (Clarias gariepinus, Heterobranchus longifilis, Chrysichthys nigrodigitatus and Chrysichthys walkeri) are reared there. In Benin, O. niloticus and C. gariepinus, whose biological and ecological characteristics for fish farming are well documented and mastered, are the two main species reared in farms exploiting cages and pens. Most fish production from cages and pens in Benin is from the Atlantic Department through Toho-Todougba Lake, in which numerous high-capacity private aquaculture farms and contribute to increase the contribution of fish aquaculture to the national fisheries production. The valorization of the other aquatic resources, such as the numerous water reservoirs available for cages and pens fish farming will therefore allow Benin to increase its capacity to feed the population. However, the disadvantages and impacts associated with these practices must be seriously monitored.Keywords: Cages, pens, fish farming, existing inland water

Evaluation histologique de la maturation des gonades chez Labeo parvis (Teleostei, Cyprinidae) au Bénin

A histological analysis was undertaken on the gonadal development of Labeo parvus Boulanger 1902, a medium-sized cyprinid from the Ouémé River, Benin. Samples were collected monthly between April 2006 and March 2007 and were examined using routine macroscopic and histoloogical techniques. Five macroscopic stages of gonad maturation were identified in the ovaries and testes and described histologically.Oocyte development was subdivided into five stages, based on the presence of chromatin nucleolus oocytes, perinucleolus oocytes, yolk vesicle oocytes, vitellogenic oocytes and mature oocytes. Four stages of spermatogenesis (spermatogonia, spermatocytes, spermatids and spermatozoa) were observed. Comparisons of macroscopic and histological observations revealed that the temporal patterns of maturation activity obtained from visual examination closely reflected the seasonal histological trend in gonad development. Histological characteristics of spent ovaries and testes ware similar to those of immature fish, indicating that L. parvus were synchronous spawners

Reproductive strategy of Labeo senegalensis Valenciennes, 1842 (Teleostei: Cyprinidae) in the Ouémé basin, Bénin.

Aspects of the reproductive biology and population structure of Labeo senegalensis were investigated in the Ouémé River between April 2005 and March 2006. Reproductive strategy was investigated using gonadosomatic index,ovarian structure and fecundity. Average size-at-first-maturity (L 50) was estimated at 29 cm TL for females and 26,7 cm TL for males. The average sex ratio (1:0,96) was not significantly different from unity. Oocyte diameter frequency distribution suggests synchronous development with a single total spawning. Absolute fecundity ranged between 12 948 and 74 832 eggs. Labeo senegalensis is a highly fecund fish that presents a seasonal cycle of reproduction from May to October during the rainy season