La croissance différentielle liée au sexe chez le tilapia (Pisces : Cichlidae), Oreochromis niloticus (Linnaeus, 1758) : contribution des facteurs génétiques, nutritionnels, comportementaux et recherche d'un relais endocrinien

L'objectif de ce travail est de caractériser les composantes de cette différence de croissance entre les mâles et les femelles chez Oreochromis niloticus, d'en préciser la période d'apparition, et de rechercher les facteurs physiologiques potentiellement impliqués dans le déterminisme du différentiel de croissance lié au sexe. L'apparition de la différence de croissance n'est pas strictement liée à l'ontogenèse gonadique, ni à la reproduction. Elle apparaît après la différenciation sexuelle et avant la maturité sexuelle. Elle n'est pas liée à une consommation alimentaire plus importante chez les mâles que chez les femelles. Elle serait liée à une faible inhibition de la croissance des femelles plus qu'à une stimulation de celle des mâles, et d'autre part que l'E2-l7B en relation avec le contrôle du métabolisme de la T3, seraient les candidats potentiels du relais endocrinien. Les résultats montrent également que le tilapia est très sensible à l'influence des interactions sociales, qui modulent très fortement la différence de croissance entre les mâles et les femelle

Spatial and temporal variation in population genetic structure of wild Nile tilapia (Oreochromis niloticus) across Africa

<p>Abstract</p> <p>Background</p> <p>Reconstructing the evolutionary history of a species is challenging. It often depends not only on the past biogeographic and climatic events but also the contemporary and ecological factors, such as current connectivity and habitat heterogeneity. In fact, these factors might interact with each other and shape the current species distribution. However, to what extent the current population genetic structure reflects the past and the contemporary factors is largely unknown. Here we investigated spatio-temporal genetic structures of Nile tilapia (<it>Oreochromis niloticus</it>) populations, across their natural distribution in Africa. While its large biogeographic distribution can cause genetic differentiation at the paleo-biogeographic scales, its restricted dispersal capacity might induce a strong genetic structure at micro-geographic scales.</p> <p>Results</p> <p>Using nine microsatellite loci and 350 samples from ten natural populations, we found the highest genetic differentiation among the three ichthyofaunal provinces and regions (Ethiopian, Nilotic and Sudano-Sahelian) (<it>R</it>_ST= 0.38 - 0.69). This result suggests the predominant effect of paleo-geographic events at macro-geographic scale. In addition, intermediate divergences were found between rivers and lakes within the regions, presumably reflecting relatively recent interruptions of gene flow between hydrographic basins (<it>R_ST</it>= 0.24 - 0.32). The lowest differentiations were observed among connected populations within a basin (<it>R_ST</it>= 0.015 in the Volta basin). Comparison of temporal sample series revealed subtle changes in the gene pools in a few generations (<it>F </it>= 0 - 0.053). The estimated effective population sizes were 23 - 143 and the estimated migration rate was moderate (m ~ 0.094 - 0.097) in the Volta populations.</p> <p>Conclusions</p> <p>This study revealed clear hierarchical patterns of the population genetic structuring of <it>O. niloticus </it>in Africa. The effects of paleo-geographic and climatic events were predominant at macro-geographic scale, and the significant effect of geographic connectivity was detected at micro-geographic scale. The estimated effective population size, the moderate level of dispersal and the rapid temporal change in genetic composition might reflect a potential effect of life history strategy on population dynamics. This hypothesis deserves further investigation. The dynamic pattern revealed at micro-geographic and temporal scales appears important from a genetic resource management as well as from a biodiversity conservation point of view.</p

Comparaison des effets d'un stéroide naturel, 11β hydroxyandrostenedione, et d'un androgène de synthèse 17α-méthyltestostérone, sur le sexe ratio chez Oreochromis niloticus

ISTA III : International Symposium on Tilapia in Aquaculture, 3., Abidjan (CIV), 1996International audienc

Comparative study of algal community in African sharptooth catfish (Clarias gariepinus, Burchell 1822) and Nile tilapia (Oreochromis niloticus, Linnaeus 1758) farming ponds

Abstract In subsistence and small‐scale fish farming, algae are an important food source for fish. Therefore, understanding their distribution and diversity in fish ponds is essential. This study aimed at characterising algae species in African sharptooth catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) farming ponds and their contribution to these species’ diet. Water samples were collected from different points of the farming pond: in rearing pond, evacuation canal of each species and decantation pond. Samples were also collected from fish stomachs and intestines. Afterwards, they were analysed with a photonic microscope for species identification using standard identification keys. The highest species richness (S) and Shannon index (H) were observed in fish rearing ponds (S = 73, H = 2.98–3.84) and the lowest in fish stomachs and intestines (S = 41, H = 1.88‐3.07). Jaccard's similarity index, ranging from 0.17 to 0.55, shows a high specific diversity of alga in the different sampling points. During the experimental period, water physicochemical parameters were within the optimum growth for algae and fish species. Since some algae species recorded are consumed by both fish species, this study recommends to select and cultivate them for fish food production

oral administration of strontium or fluoresceine for marking of Orechromis niloticus fry

National audienc

It’s not right but it’s permitted: Wording effects in moral judgement

This study aims to provide evidence about two widely held assumptions in the experimental study of moral judgment. First, that different terms used to ask for moral judgment (e.g., blame, wrongness, permissibility…) can be treated as synonyms and hence used interchangeably. Second, that the moral and legal status of the judged action are independent of one another and thus moral judgment have no influence of legal or other conventional considerations. Previous research shows mixed results on these claims. We recruited 660 participants who provided moral judgment to three identical sacrificial dilemmas using seven different terms. We experimentally manipulated the explicit legal status of the judged action. Results suggest that terms that highlight the utilitarian nature of the judged action cause harsher moral judgments as a mechanism of reputation preservation. Also, the manipulation of the legal status of the judged action holds for all considered terms but is larger for impermissibility judgments. Taken as a whole, our results imply that, although subtle, different terms used to ask for moral judgment have theoretically and methodologically relevant differences which calls for further scrutiny