Macrobrachium prawns are voracious predators of the freshwater snails that host the flatworms responsible for bilharzia (schistosomiasis), a health burden in many African countries. A novel strategy to decrease the disease in Africa involves the use of prawns as biocontrol agents of the snails. Although the endemic African river prawn Macrobrachium vollenhovenii is a natural candidate for aquaculture and biocontrol, efforts to domesticate it have been unsuccessful to date, and it is not available in the large quantities required for aquaculture and biocontrol. The Asian giant prawn Macrobrachium rosenbergii has been cultured worldwide for decades. Recently, novel biotechnologies were developed to create monosex (all-male) non-breeding populations for aquaculture that we suggest are also ideal for biocontrol in Africa. Since the above 2 prawn species are of the same genus, exhibit similar sizes and require a female pre-mating molt prior to egg fertilization, the potential for cross-breeding between the 2 species must be tested. To assure that all-male populations of M. rosenbergii will not pose such an ecological threat, we carried out cross-breeding experiments with M. vollenhovenii. Both interspecies encounters and attempts at artificial insemination revealed that fertilization does not occur between the 2 species. Our results demonstrate both behavioral and physiological pre-zygotic reproductive barriers between these species. We suggest that all-male M. rosenbergii can be used as an aquaculture species and as a biocontrol agent in areas where M. vollenhovenii occurs without concern for hybridization.

The objective of the study was to evaluate the influence of physicochemical parameters of water on the spatial distribution of snail intermediate hosts of human schistosomes in the Senegal River Delta. Eight water points in three endemic villages for schistosomiasis were selected for biweekly monitoring of snail numbers and physicochemical parameters of water at the beginning of the rainy season. The results show that the spatial distribution of snail populations is a function of certain parameters. The pH, the dissolved oxygen and its saturation, and the temperature have a positive influence on the Bulinus and Biomphalaria, while the conductivity, the speed of flow, and the salts (phosphates, salinity, and nitrates) seem to act negatively on the populations of these snails.

The distribution of the intertidal barnacle Chthamalus montagui spans the West Mediterranean Sea and the Northeast Atlantic shores of Europe and West Africa. Knowledge of the phylogeography of this species has been limited to the Mediterranean and the European shores of the Atlantic. The present study considers the populations of West Europe, but also focuses on the overlooked populations of West Africa. We performed a molecular analysis using two markers: the mitochondrial COI gene and the nuclear rRNA ITS gene. Whereas ITS proved to be non‐informative, COI has demonstrated that the East Atlantic population of C. montagui comprises two genetically distinct clades: a northern clade that ranges from Mauritania to Scotland and a southern clade that comprises the populations from Senegal. These clades are separated by the Cape Verde Front, which stretches west of the upwelling area off Mauritania. We consider these clades as two cryptic species of the nominal species C. montagui.

Fish farming in Senegal encounters many difficulties, especially during the first life stages, which are more demanding for food and more sensitive to variations in the physicochemical parameters. Most of the species of aquaculture interest have offspring whose size at birth is very small, thus requiring a particular rich food adapted to the size of the mouth (e.g. live preys which are very rich in nutritive reserves). The objective of this study was to set up a production system of live prey, daphnia for the feeding of fish fry. It consisted of culturing microalgae that were used to fed daphnia reared to fed the fry of the African catfish, Clarias gariepinus. The temperature and dissolved oxygen content in the culture and rearing media were monitored throughout the experiment. The results on species identification showed that the cultured microalgae and reared daphnia species are Microcystis sp and Daphnia magna, respectively. Analyses of algal biomass and daphnia abundance show an increase in these parameters with time. Temperature variations do not affect algal biomass, daphnia abundance and fry growth. On the other hand, a decrease in dissolved oxygen content below a certain threshold (6mg/l) leads to a decrease in algal biomass and daphnia abundance. Among the three feeding rates 1.5g, 3g, 4.5g (the equivalent of 0.5L, 1L, and 1.5L of microalgae, respectively) that were used to feed daphnia, the feeding rate of 3g of biomass corresponding to 1L is more adequate as it gave the best production. The comparison of the effects of the types of feed shows that live daphnia give better growths of C. gariepinus fry than the artificial feed, which may be due to their adequate size and nutrient richness. Thus, this study contributes to the establishment of live prey production systems to boost local aquaculture development and demonstrates the importance of daphnia for the feeding of early fish life stages.

Cette étude a été réalisée en 2017 à la station de l'Agence Nationale de l'Aquaculture de Richard-Toll (vallée du fleuve Sénégal) dans le cadre du projet PISCI/FNRAA/WAAPP2 Commandité sur l'Adaptation, Diffusion et Adoption de technologies de production en masse d'alevins mâles de Tilapia (Oreochromis niloticus) au Sénégal financé par le Fonds d'Impulsion de la Recherche Agro-Alimentaire du Sénégal (FNRAA). Face à un déficit d'alevins de tilapia confronté par les producteurs et à la difficulté de sexage manuel, ce travail oeuvre à produire et fournir en quantité suffisante des alevins mono-sexe mâles de qualité aux producteurs et de transférer la technologie aux agences d'exécution de l'aquaculture et aux promoteurs privés. Pour ce faire, une activité de production en masse d'alevins mâles de la souche locale du Tilapia du Nil de la vallée du fleuve Sénégal a été testée en ajoutant l'hormone 17 alpha méthyl-testostérone dans l'aliment fourni à des alevins dont le sac vitellin vient d'être résorbé pendant 28 jours. Cette expérience a permis de produire 21 168 alevins mâles de Tilapia (O. niloticus) en 3 mois et de cerner les limites de la production en masse d'alevins de la souche du Tilapia du Nil de la vallée du fleuve Sénégal au niveau de l'écloserie de l'ANA installée à Richard-Toll. Par conséquent, cette étude peut être reconduite en utilisant d'autres méthodes d'inversion sexuelle du Tilapia.