Stratégie de reproduction du carangidae Trachinotus teraia cuvier, 1832 dans la lagune ebrié (Côte d’Ivoire)

La reproduction de Trachinotus teraia a été étudiée dans la lagune Ebrié au cours de campagnes mensuelles pendant deux années consécutives (février 2004 à janvier 2006). Cette étude se situe dans le cadre d’acquisition de connaissances sur la biologie de Trachinotus teraia en vue d’évaluer son potentiel aquacole. Au total, 1806 spécimens dont 739 mâles, 746 femelles et 321 juvéniles ont été capturés à l’aide de filets maillants (mailles : 10, 14, 20, 25, 30, 35, 40, 50, 80 et 100 mm) et examinés. En ce qui concerne les paramètres déterminés, le sex-ratioest 1 : 1. La taille de première maturité sexuelle (LF50) est atteinte à 199 mm et 212 mm respectivement chez les mâles et les femelles. Le plus petit individu mâle mature capturé mesure 154 mm (LF) et pèse 86,85 g tandis que la plus petite femelle mature capturée mesure 170 mm (LF) et pèse 118,24 g. Les variations mensuelles des indices gonadosomatique(IGS), hépato-somatique (IHS), du facteur de condition (K) et des stades de maturité indiquent deux périodes de reproduction. La longue période de ponte se situe de février à avril tandis que la courte période de ponteintervient de septembre à octobre. Les réserves hépatiques semblent être mobilisées pour assurer le coût énergique de la reproduction. La fécondité absolue varie entre 15 053 et 2 058 907 ovocytes pour des femelles de tailles comprise entre 260 et 582 mm. Les moyennes des diamètres ovocytaires de ces femelles sont deReproductive biology of Trachinotus teraia was studied in the Ebrié lagoon during two years (from February 2004 to January 2006) by monthly sampling using gill nets with stretched mesh sizes 10, 14, 20, 25, 30, 35, 40, 50, 80, and 100 mm). Basic biological information was collected to describe some aspects of reproductive biology of T. teraia for use in aquaculture programmes. A total of 1806 specimens were examined (739 males, 746 females and 321 juveniles. The sex ratio was 1:1. The size at first sexual maturity (LF50) is reached at 199 mm and 212 mm respectively for the males and females. The smallest mature male was 154 mm (LF) and weighed 86.85 g while in female, this maturity occurred at 170 mm and 118.24 g. The monthly variations of the gonado-somatic index (GSI) and hepato-somatic index (HSI), the condition factor (K) and maturation stages indicated two periods of reproduction. The long period and the short period were respectively from February to April and from September to October. The hepatic reserves seem to be mobilized to ensure the energetic cost of the reproduction. The absolute fecundity was ranged from 15 053 to 2 058 907 oocytes for females of 260 and 582 mm (FL). The averages of the oocytes diameters ranged between 449.53 ± 152.49 μm and 393.29±126,85 μm, respectively for the large and the short periods of reproduction.Mots clés : Carangidae, Trachinotus teraia, reproduction, sex-ratio, fécondité, Côte d’Ivoire.

Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.Comment: 4 pages, 5 figure

Short Intense Laser Pulse Collapse in Near-Critical Plasma

It is observed that the interaction of an intense ultra-short laser pulse with an overdense gas jet results in the pulse collapse and the deposition of a significant part of energy in a small and well localized volume in the rising part of the gas jet, where the electrons are efficiently accelerated and heated. A collisionless plasma expansion over 150 microns at a sub-relativistic velocity (~c/3) has been optically monitored in time and space, and attributed to the quasistatic field ionization of the gas associated to the hot electron current. Numerical simulations in good agreement with the observations suggest the acceleration in the collapse region of relativistic electrons, along with the excitation of a sizeable magnetic dipole that sustains the electron current over several picoseconds. Perspectives of ion beam generation at high repetition rate directly from gas jets are discussed

Investigation of rodent reservoirs of emerging pathogens in Côte d'Ivoire, West Africa

Background: One of the main health problems in West Africa remains upsurge of emerging pathogens. Ebola virus disease outbreak occurred in 2014 in Liberia, Guinea and Sierra Leone, Monkeypox virus in Nigeria in 2017 and most recently Lassa virus in Nigeria, Togo and Benin in 2018.  These pathogens have animal reservoirs as vectors for transmission. Proper investigation of the pathogens in their rodent vectors could help  reduce and manage their emergence and spread. Methodology: This study was conducted with an approval from the Côte d’Ivoire Bioethics Community. Small mammal trappings were carried out in  9 sites within three zones namely, peri-urban, peri-rural and protected areas. Liver, lung and kidney tissues from trapped small mammals were  sampled in accordance with the recommended conditions of biosafety and bioethics. The organs were transported in liquid nitrogen to the  laboratory. Molecular tests were used to detect pathogens. Orthopoxviruses and Monkeypox virus were detected in the organs by PCR using  consensus primers targeting the virus surface membrane haemagglutinin (HA) genes, while Leptospira species were detected by PCR using primers  targeting the rrs and lfb1 genes. Results: Out of 4930 night-traps, 256 (5.19%) small mammals were trapped including Crocidura, Rattus, Lophuromys, Praomys, Mus and Mastomys.  Leptospira species were detected in 6 genera from 7 study sites and the infected small mammals accounted for 13.3%. Leptospira sp was detected  mainly in the rodent vector genera Rattus (32.3%), Lophuromys (29.0%), and Praomys (16.1%). Three species of Leptospira were detected and  Leptospira interrogans was the most common frequent species (74.2%). Monkeypox virus was not detected from studied small mammals. Conclusion: The initial data from our investigation indicates the presence of Leptospira sp in rodent vectors, Rattus, Lophuromys and Praomys,  which are the potential small mammalian reservoirs of this pathogen in Cote d’Ivoire

Stock assessment and population dynamics of Senegal Jack, Caranx senegallus Cuvier, 1833, from industrial fishery of Cote d’Ivoire (West Africa)

Monthly data of C. senegallus length composition, was recorded from the continental shelf of Côte d’Ivoire from March 2016 to February 2018. The population parameters such as length-frequency distribution, length-weight relationship, growth, mortality, exploitation ratio and length at first capture of this species were investigated to get information for effective management of this fish, by applying Beverton and Holt (1957), virtual population analysis (VPA), using the FISAT Tool II. The lengthfrequency distribution of 804 samples showed polymodal distribution. The folk length ranged from 16.10 to 47.00 cm with a mean equal to 25.68 ± 0.23 cm. The statistical analysis shows that the combined sexes (“b” = 2.9793), and male (“b” = 3.0199) growth is isometric. However, female (“b” = 2.9489) growth is negative allometric. The estimated growth parameters were: FL ∞ = 51.45 cm, K = 0.46 year-1 and t0 = -0.31 year-1. The length at first capture was 19.04 cm (FL). The current exploitation rate (E = 0.33), was lower than the optimum level (E = 0.36). VPA indicate that the fish which die by natural mortality are higher than those which die by fishing mortality. These results show that the current stock of C. senegallus is not overexploited. Keywords: Carangidae, Caranx senegallus, Stock, Population parameters, Fishery   English Title: Gestion des stocks et dynamique des populations du carangue du sénégal, caranx Senegallus Cuvier, 1833, de la pêche industrielle de côte d’ivoire (Afrique de l’ouest) Les données mensuelles sur la composition en taille de C. senegallus, ont été enregistrées sur le plateau continental de la Côte d’Ivoire entre mars 2016 et février 2018. Les paramètres de population tels que la distribution des fréquences de taille, la relation longueur-poids, la croissance, la mortalité, le taux d’exploitation et la taille de première capture de cette espèce ont été étudiés pour obtenir des informations permettant une gestion efficace du stock de ce poisson, par la méthode de Beverton et Holt (1957) et l’analyse de population virtuelle, grâce au logiciel FISAT II. La distribution des fréquences de taille de 804 individus a montré une distribution polymodale. La longueur à la fourche variait de 16,10 à 47,00 cm avec une moyenne égale à 25,68 ± 0,23 cm. L’analyse statistique montre que la croissance des sexes combinée (“b” = 2,9793) et des mâles (“b” =  3,0199) est isométrique. Tandis que, la croissance des femelles (“b” = 2,9489) est allométrique négative. Les paramètres de croissance estimés ont  été les suivants : FL ∞ = 51,45 cm, K = 0,46 an-1 et t0 = - 0,31 an-1. La longueur à la première capture a été de 19,04 cm (FL). Le taux d’exploitation  actuel (E = 0,33), était inférieur au niveau optimal (E = 0,36). L’Analyse des Populations Virtuelles indique que les poissons qui meurent par mortalité naturelle sont plus élevés que ceux qui meurent par mortalité par pêche. Ces résultats montrent que le stock actuel de C. senegallus n’est pas  surexploité. Mots clés : Carangidae, Caranx senegallus, Stock, Paramètres des populations, Pêcheri